classwork: Erythema ab igne

pubmed search 57 free full text case report articles. 29 here in text form.

Received 04/27/2018

Review began 05/07/2018

Review ended 05/13/2018

Published 05/16/2018

Aria et al. This is an open access

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Erythema Ab Igne from Heating Pad Use: A

Report of Three Clinical Cases and a

Differential Diagnosis

Alexander B. Aria , Leon Chen , Sirunya Silapunt

1. Dermatology, University of Texas Mcgovern Medical School at Houston

 Corresponding author: Sirunya Silapunt, sirunya.silapunt@uth.tmc.edu

Disclosures can be found in Additional Information at the end of the article

Abstract

Erythema ab igne is an asymptomatic cutaneous disorder characterized by erythematous

reticulated hyperpigmentation resulting from chronic exposure to infrared radiation in the

form of heat. We report three cases of erythema ab igne from chronic heating pad use over a

duration of six months to three years. The lesions were asymptomatic in all three patients and

were incidental skin findings in two patients, unrelated to their chief complaints. This

illustrates the importance of recognizing the morphology and distribution of erythema ab igne.

Additionally, knowledge of similarly presenting cutaneous diseases is important to distinguish

erythema ab igne from other more worrisome entities that would require further evaluation.

Our patients were informed of the benign nature of this condition and were told that cessation

of heating pad use would likely result in the resolution of their lesions.

Categories: Dermatology, Internal Medicine, Medical Education

Keywords: erythema ab igne, heating pad

Introduction

Chronic exposure to heat and infrared radiation may result in reticulated erythematous and

hyperpigmented skin lesions known as erythema ab igne. This benign condition is

asymptomatic and is traditionally associated with stoves or open fires. The hyperpigmentation

of erythema ab igne occurs in relation to heat exposure and usually resolves with the cessation

of this exposure; however, permanent hyperpigmentation can occur. We report three cases of

erythema ab igne from chronic heating pad use.

Case Presentation

Patient 1

Our first patient was a 76-year-old Caucasian female with skin color changes on her back which

were noticed by her husband a few weeks prior to presentation. The patient had a history of

generalized pain with no identifiable etiology and had been using an electrical heating pad for

12 months for pain alleviation. As she became bedridden due to her intractable pain, she often

laid on the electrical heating pad for at least six consecutive hours for several months and

denied any associated burning or discomfort. Physical examination revealed reticulated, illdefined, reddish-brown patches in a cape-like distribution down the patient’s back (Figure 1).

1 1 1

Open Access Case

Report DOI: 10.7759/cureus.2635

How to cite this article

Aria A B, Chen L, Silapunt S (May 16, 2018) Erythema Ab Igne from Heating Pad Use: A Report of Three

Clinical Cases and a Differential Diagnosis . Cureus 10(5): e2635. DOI 10.7759/cureus.2635

FIGURE 1: Patient 1. Erythema ab igne

Erythematous reticulated hyperpigmentation on the back.

The patient was informed that her lesions were due to chronic heat exposure and was advised to

discontinue using her heating pad. At a follow-up visit 18 months later, her lesions had

resolved.

Patient 2

Our second patient was a 52-year-old Caucasian female seen as an inpatient consult due to the

presence of hyperpigmented lesions on her abdomen and upper thighs. She had been admitted

2018 Aria et al. Cureus 10(5): e2635. DOI 10.7759/cureus.2635 2 of 7

to the hospital due to a brain abscess and had undergone a craniotomy for abscess drainage.

The patient’s mental status was impaired and a history could not be taken. The primary team

stated that the patient’s skin lesions had been present since admission; however, their exact

duration was unknown. On examination, the patient had lace-like hyperpigmented patches on

the lower abdomen and upper thighs (Figure 2).

FIGURE 2: Patient 2: Erythema ab igne

Reddish-brown reticulated patches on the lower abdomen.

The diagnosis of erythema ab igne was given, and the care team was reassured of the benign

nature of this condition. Several days later, additional history was obtained from the patient’s

husband when he became available. He reported that the patient had uterine fibroids and had

been using a heating pad for more than eight hours daily for the past three years to alleviate

lower abdominal pain. The husband was informed that the heating pad was the culprit of the

patient’s hyperpigmented skin and was instructed to discontinue its use.

Patient 3

2018 Aria et al. Cureus 10(5): e2635. DOI 10.7759/cureus.2635 3 of 7

Our third patient was a 50-year-old Caucasian female seen in our clinic for a full body skin

examination. Hyperpigmented reticulated patches on the lower back were noted incidentally

during her physical examination (Figure 3).

FIGURE 3: Patient 3: Erythema ab igne

Reticulated hyperpigmented patches on the lower back.

The patient was not aware of the lesions but reported that she had used a heating pad weekly

for lower back pain for at least six months until the pain resolved a few months prior to her

visit. The patient was informed that she had erythema ab igne due to chronic heat exposure and

was counseled on its benign course.

Discussion

In modern society, chronic exposure to heat from laptops [1] or heating pads [2] has become the

most common cause of erythema ab igne. Patients will often overlook these skin lesions due to

their symptomless nature. Our three cases demonstrate the importance of recognizing

morphology and distribution when diagnosing this cutaneous condition, especially in the case

of our second patient who was unable to provide any history due to impaired mental status.

Knowledge of similarly appearing cutaneous diseases is important for determining whether the

underlying cause of a patient’s erythematous hyperpigmented lesions is benign, such as

erythema ab igne, or a more worrisome entity that would require further work up.

Other conditions with a similar reticulated appearance as erythema ab igne include livedo

reticularis, livedo racemosa, cutis marmorata, and cutis marmorata telangiectatica congenita

(Table 1) [3].

2018 Aria et al. Cureus 10(5): e2635. DOI 10.7759/cureus.2635 4 of 7

Diagnosis

Population

affected

Clinical morphology Distribution Blanchable Associations Treatment

Erythema ab

igne

Most

frequently

middle-aged

or older

women;

recent

reports of

young adults

Localized reticulated

erythema that

correlates with a

vascular pattern;

becomes increasingly

hyperpigmented with

time

Skin surface

exposed to heating

source

Early – yes;

late – no

Due to chronic

heat exposure;

development of

squamous cell

carcinoma or

Merkel cell

carcinoma has

been reported

Removal of

heat source

decreasing

the

exposure

duration;

can try 5-

fluorouracil

Livedo

reticularis

Young to

middle-aged

women

Mottled, net-like

pattern of

hyperpigmentation

that is uniform,

symmetric, and

reversible

Primarily on the

extremities

Yes

Can be idiopathic;

due to an

underlying

disease (APS);

physiologic

Treat

underlying

cause

Livedo

racemosa

Young to

middle-aged

women

Mottled, net-like

pattern of

hyperpigmentation

that is permanent with

“irregular” broken

netting

Primarily the

proximal limbs and

trunk

Partially

Can be associated

with Sneddon

syndrome, SLE,

APS, etc.

Treat

underlying

cause

Cutis

marmorata

Neonates,

infants

Fluctuant, mottled,

net-like pattern of

hyperpigmentation

Primarily the lower

extremities

Yes

Exposure to cold

temperature

Rewarming

Cutis

marmorata

telangiectatica

congenita

Neonates

Reticulated vascular

pattern that is

persistent

Primarily limited to

a single extremity;

if trunk is involved,

there is usually

sharp demarcation

at the midline

Partially

Congenital

disorder

associated with

limb asymmetry

and vascular

malformations as

well as neurologic

or ocular

abnormalities

Usually

improves

with time

TABLE 1: Erythema ab igne and its clinical mimickers

APS – antiphospholipid syndrome; SLE – systemic lupus erythematous

Livedo reticularis is a benign disorder that most often affects young females; can be

physiologic, primary, or idiopathic; and is characterized by a persistent or transient reticulated

cyanotic pattern [4]. Physiologic livedo reticularis is also known as cutis marmorata [4]. It

commonly occurs after exposure to cold temperatures and slowly resolves with rewarming.

2018 Aria et al. Cureus 10(5): e2635. DOI 10.7759/cureus.2635 5 of 7

Unlike livedo reticularis, livedo racemosa is associated with a number of pathological

conditions such as systemic lupus erythematosus, antiphospholipid syndrome, and Sneddon

syndrome, a non-vasculitic condition presenting with reticulated hyperpigmented lesions and

cerebrovascular disease [3-4]. Livedo racemosa is characterized by a violaceous broken

reticulated pattern that appears more generalized, widespread, and irregular in shape than

livedo reticularis [5]. Cutis marmorata telangiectatica congenita is a congenital disorder which

appears as reticulated erythema that usually improves with time and is sometimes associated

with limb asymmetry and vascular malformations as well as neurologic or ocular abnormalities

[6].

Although erythema ab igne is primarily a clinical diagnosis, histopathology may aid in

confirming the diagnosis. Histopathology often demonstrates epidermal keratinocyte atypia,

elastosis in the dermis and occasionally liquefaction degeneration of the basal layer, as well as

melanin incontinence and hemosiderin in the dermis. Staining with elastic stain Verhoeff-Van

Gieson stain can also support the diagnosis of erythema ab igne [7-8].

When evaluating a patient with reticulated hyperpigmented erythema, the diagnosis of

erythema ab igne should be considered if there is a history of chronic heat exposure with a

corresponding distribution. Malignancy workup may be necessary if there is a high index of

suspicion that the heating pad is being used to alleviate pain due to underlying primary

malignancy, metastatic disease, or chronic pancreatitis [9]. Although erythema ab igne is

typically benign and will likely resolve with discontinuation of heat exposure, secondary

development of cutaneous malignancies such as squamous cell carcinomas and Merkel cell

carcinomas within the affected area have been reported in the literature [10-11]. If a nonhealing wound or ulceration is noted within an erythema ab igne lesion, a skin biopsy is

warranted to rule out malignancy. There is no precise data on the duration of heating pad usage

required to develop erythema ab igne; however, it is generally recommended that the treatment

time should not exceed 30 minutes [12].

Conclusions

The above three cases illustrate the importance of recognizing the morphology and distribution

of erythema ab igne apart from other clinical mimickers. Complete cessation of heating pad use

typically results in resolution of these erythema ab igne lesions.

Additional Information

Disclosures

Human subjects: Consent was obtained by all participants in this study. Conflicts of interest:

In compliance with the ICMJE uniform disclosure form, all authors declare the following:

Payment/services info: All authors have declared that no financial support was received from

any organization for the submitted work. Financial relationships: All authors have declared

that they have no financial relationships at present or within the previous three years with any

organizations that might have an interest in the submitted work. Other relationships: All

authors have declared that there are no other relationships or activities that could appear to

have influenced the submitted work.

References

1. Salgado F, Handler MZ, Schwartz RA: Erythema ab igne: new technology rebounding upon its

users?. Int J Dermatol, 57:393-396. 10.1111/ijd.13609

2. Milchak M, Smucker J, Chung CG, Seiverling EV: Erythema ab igne due to heating pad use: a

case report and review of clinical presentation, prevention, and complications. Case Rep Med.

2016, 2016:1862480. 10.1155/2016/1862480

2018 Aria et al. Cureus 10(5): e2635. DOI 10.7759/cureus.2635 6 of 7

3. Parsi K: Dermatological manifestations of venous disease. Part II: reticulate eruptions .

Australian & New Zealand Journal of Phlebology. 2008,

4. Sajjan VV, Lunge S, Swamy MB, Pandit AM: Livedo reticularis: a review of the literature .

Indian Dermatol Online J. 2015, 6:315-321. 10.4103/2229-5178.164493

5. Uthman IW, Khamashta MA: Livedo racemosa: a striking dermatological sign for the

antiphospholipid syndrome. J Rheumatol. 2006, 33:2379-2382.

6. Kienast AK, Hoeger PH: Cutis marmorata telangiectatica congenita: a prospective study of 27

cases and review of the literature with proposal of diagnostic criteria. Clin Exp Dermatol.

2009, 34:319-323. 10.1111/j.1365-2230.2008.03074.x

7. Johnson WC, Butterworth T: Erythema ab Igne elastosis . Arch Dermatol. 1971, 104:128-131.

10.1001/archderm.1971.04000200016004

8. Finlayson GR, Sams WM Jr, Smith JG Jr: Erythema ab igne: a histopathological study . J Invest

Dermatol. 1996, 46:104-108. 10.1038/jid.1966.15

9. Mok DW, Blumgart LH: Erythema ab igne in chronic pancreatic pain: a diagnostic sign . J R Soc

Med. 1984, 77:299-301. 10.1177/014107688407700409

10. Sigmon JR, Cantrell J, Teague D, Sangueza O, Sheehan DJ: Poorly differentiated carcinoma

arising in the setting of erythema ab igne. Am J Dermatopathol. 2013, 35:676-678.

10.1097/DAD.0b013e3182871648

11. Jones CS, Tyring SK, Lee PC, Fine JD: Development of neuroendocrine (Merkel cell) carcinoma

mixed with squamous cell carcinoma in erythema ab igne. Arch Dermatol. 1988, 124:110-114.

10.1001/archderm.1988.01670010074024

12. Theratherm Operating Manual. (2018). Accessed: January 5, 2018:

https://therathermcanada.com/wp-content/uploads/2016/10/Theratherm-Heating-PadManual.pdf.

2018 Aria et al. Cureus 10(5): e2635. DOI 10.7759/cureus.2635 7 of 7

Ravindran R. BMJ Case Rep 2017. doi:10.1136/bcr-2014-203856 1

Description

Prolonged abdominal heat application in an individual with diabetes and gastroparesis leads to the

development of erythema ab igne. Practitioners

should be aware of the various ways that erythema

ab igne can present.1

Erythema ab igne is due to prolonged heat exposure (43–47°C) which causes damage to superficial

vascular plexus leading to vasodilation, erythema

and haemosiderin deposition which clinically

appears as hyperpigmentation.2

A 28-year-old man with type 1 diabetes and

gastroparesis had presented with vomiting

and abdominal pain. Abdominal examination

revealed a erythematous, reticulated, macular

and non blanchable pigmentation, (figure 1).

The patient used to apply hot water bottles for

abdominal pain relief.

Erythema ab igne can be associated with

epidermal atrophy and scaling.1

The lesions may

become keratotic and bullous (rare) with a slightly

burning sensation.2 3

Important differentials include other reticulated conditions such as livedo reticularis and

livedoid vasculitis, cutis marmorata, poikiloderma atrophicans vasculare and cutaneous

T-cell lymphoma.

Management is mainly removing the heat

source. 5-fluorouracil is recommended if the

lesion shows precancerous changes and can help

clear epithelial atypia. Topical tretinoin or laser

is advocated for improving skin pigmentation.4 5

Biopsy of the lesion was not performed in

the patient as it was clear that the lesion was

due to application of heat source as the lesion

started to fade during the patient’s hospital

stay.6

Biopsy is usually recommended to rule out

cancer if lesions are not fading after the removal

of heat source.7

Contributors RR is the sole author of this manuscript.

Competing interests None declared.

Patient consent Obtained.

Provenance and peer review Not commissioned; externally

peer reviewed.

Author note A young patient hadpresented with abdominal

pain and vomiting in the evening. He was a type 1 diabetic with

gastroparesis. On admission, high glucose levels were noted

and he was treated overnight with variable rate insulin infusion

to control his glucose levels as he was unable to eat due to his

vomiting and abdominal pain.When he was seen by the on-call

medical consultant, he was found to be lying in bed in a curled

up position and with his hand on his abdomen. Examination of

his abdomen revealed erythema ab igne lesion and the patient

informed that hehad been using hot water bottles/bags to relieve

himself of his pain. An erythema ab igne lesions are usually found

in elderly. Patients who often sitnear the fire during winter time to

keep themselves warn, this lesion presenting in a young man with

diabetic gastroparesis was striking which indicated the severity

of the pain secondary to gatroparesis. A quick literature search

did not reveal any gastroparetic patient presenting with this type

of lesion, although an astute physician can make a diagnosis of

hypothyroidism when such lesion presents in the shin area of

hypothyroid patients due to theirproximity to heating devices

to keep themselves warm. It was felt that this would be a good

pictorial case presentation for general physicians so that they can

be aware of the different ways of presentation of erythema ab

igne. Also the lesion can also be precancerous and is one of the

differentials.

permitted unless otherwise expressly granted.

References

1 Helm TN, Spigel GT, Helm KF, et al. Erythema ab igne caused by a car

heater. Cutis 1997;59:81–2.

2 Bolognia JL, Jorizzo JL, Schaffer JV. Dermatology. 3rd edn. China:

Elsevier Saunders, 2012.

3 Goldsmith LA, Katz SI, Gilchrest BA, et al. Fitzpatrick's dermatology

In general medicine. 8th edn. USA: Mcgraw Hill, 2012.

4 Champion RH, Burton JL, Burns DA, eds. Rook/Wilkinson/

Ebling Textbook of Dermatology. 6th edn. UK: Blackwell Science,

1998.

5 Salgado F, Handler MZ, Schwartz RA, et al. Erythema ab igne: new

technology rebounding upon its users? Int J Dermatol 2017. [Epub

ahead of print: 30 Mar 2017].

Erythema ab igne in an individual with diabetes

and gastroparesis

Ravikumar Ravindran1,2

Images in…

To cite: Ravindran R. BMJ

Case Rep Published Online

First: [please include Day

Month Year]. doi:10.1136/

bcr-2014-203856

Diabetes and Endocrinology,

Cardiff University

University Hospital Wales

Correspondence to

Dr Ravikumar Ravindran,

dr.ravimrcp@gmail.com,

dr.ravimrcp@gmail.com

Accepted 22 September 2017

Figure 1 Erythema ab igne in an individual with

diabetes and gastroparesis.

Learning points

► Erythema ab igne indicates the severity of the

underlying cause for example, pain thereby

leading to prolonged heat application.

► Practitioners need to be aware of the different

ways of presentation of erythema ab igne.

2 Ravindran R. BMJ Case Rep 2017. doi:10.1136/bcr-2014-203856

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Images in…

6 South AM, Crispin MK, Marqueling AL, et al. A hyperpigmented reticular rash in a

patient on peritoneal dialysis. Perit Dial Int 2016;36:699–700.

7 Erythema ab igne | DermNet New Zealand. Dermnetnz.org 2017. cited 6 Aug 2017

https://www.dermnetnz.org/topics/erythema-ab-igne/

Academic Editor: Bruce J. Nicholson

Received: 5 August 2025

Revised: 1 September 2025

Accepted: 27 September 2025

Published: 29 September 2025

Citation: Scurtu, F.; Scurtu, L.G.;

Baus,ic, A.I.G.; Petca, A.; Mehedint,u, C.

Erythema ab igne—A Potential

Cutaneous Marker of Chronic Heat

Use in Patients with Endometriosis: A

Narrative Literature Review and a

Case Report. Life 2025, 15, 1533.

https://doi.org/10.3390/

life15101533

Licensee MDPI, Basel, Switzerland.

This article is an open access article

distributed under the terms and

conditions of the Creative Commons

Attribution (CC BY) license

(https://creativecommons.org/

licenses/by/4.0/).

Case Report

Erythema ab igne—A Potential Cutaneous Marker of Chronic

Heat Use in Patients with Endometriosis: A Narrative Literature

Review and a Case Report

Francesca Scurtu 1,2 , Lucian G. Scurtu 3,* , Alexandra Irma Gabriela Baus,ic 1,4 , Aida Petca 1,5

and Claudia Mehedint,u

1,2

1 Department of Obstetrics and Gynecology, “Carol Davila” University of Medicine and Pharmacy,

050474 Bucharest, Romania; francesca.scurtu@umfcd.ro (F.S.); alexandra.bausic@umfcd.ro (A.I.G.B.);

aida.petca@umfcd.ro (A.P.); claudia.mehedintu@umfcd.ro (C.M.)

2 Department of Obstetrics and Gynecology, Filantropia Clinical Hospital, 030084 Bucharest, Romania

3 Department of Dermatology I, Colentina Clinical Hospital, “Carol Davila” University of Medicine and

Pharmacy, 020125 Bucharest, Romania

4 Department of Obstetrics and Gynecology, “Prof. Dr. Panait Sîrbu” Obstetrics and Gynecology Hospital,

060251 Bucharest, Romania

5 Department of Obstetrics and Gynecology, Elias University Emergency Hospital, 011461 Bucharest, Romania

* Correspondence: lucian.scurtu@umfcd.ro

Abstract

Erythema ab igne (EAI), also known as “hot water bottle rash” or “toasted skin syndrome”,

is a benign cutaneous condition caused by chronic exposure to low-level infrared heat. It

typically begins as transient erythema and evolves into a reticulated brown pigmentation

with telangiectasias. A skin biopsy, ideally taken from the central area of the hyperpigmented lesion, is recommended to exclude differential diagnoses. Although usually benign,

EAI has been associated with rare malignant transformations, supported only by low-level

evidence. Elimination of the heat source is essential, and topical treatments such as hydroquinone or retinoids may be considered, while agents like 5-fluorouracil or imiquimod

are reserved for dysplastic lesions. Women with endometriosis frequently use heating

devices to alleviate dysmenorrhea and chronic pelvic pain. However, prolonged or inappropriate heat application can lead to chronic thermal injury, including EAI, and may

delay medical consultation. While controlled trials confirm short-term analgesic efficacy of

heat therapy, extrapolating these findings to unrestricted home use without standardized

safety recommendations can be misleading. EAI illustrates the broader impact of chronic

pain in endometriosis, linking cutaneous manifestations with neuroplastic alterations and

psychiatric comorbidities. A nuanced approach combining patient education on safe use of

heat, close dermatologic monitoring, and multidisciplinary pain management is warranted.

Keywords: endometriosis; erythema ab igne; toasted skin syndrome; hot bottle rash; squamous

cell carcinoma; Marjolin ulcer; heating device; pain; deep endometriosis; laparoscopy

1. Introduction

Erythema ab igne (EAI) represents a benign skin finding secondary to chronic exposure

to low levels of external infrared heat, typically around but below the burn threshold

(43–47 ◦C). EAI was previously described as the “hot water bottle rash” or “toasted skin

syndrome,” as it typically appeared on the pretibial skin of elderly individuals due to the

use of space heaters. Nowadays, the main triggers are resting laptops for a prolonged time

Life 2025, 15, 1533 https://doi.org/10.3390/life15101533

Life 2025, 15, 1533 2 of 14

(professional EAI) and using heating devices to alleviate chronic pain. Chronic EAI has the

potential to evolve into skin cancer [1].

Chronic pelvic pain (CPP) is recurrent or persistent pelvic pain that lasts at least

six months [2]. It is encountered in up to 25% of menstruating persons worldwide. Between 40 and 87% of CPP patients have endometriosis. Endometriosis arises as estrogendependent and progesterone-resistant extrauterine lesions that induce a chronic inflammation, provoking pain and infertility. Endometriosis-associated pain usually debuts

after menarche and is secondary to retrograde menstruation and neuro-angiogenic factors

that activate endometrial cells into developing endometrial lesions [3]. Up to 37% of patients with pelvic endometriosis develop deep endometriosis (DE), involving the Douglas

pouch, the uterosacral ligaments, the posterior vaginal wall, the colorectal tract, and the

urinary tract. Severe pain (dysmenorrhea, deep dyspareunia, intermenstrual pelvic pain) is

encountered in more than 90% of DE patients [4].

The 2022 ESHRE Guidelines showed that non-medical management strategies, including heating devices, are widely used by patients with endometriosis to alleviate severe pain.

Still, EAI is not traditionally linked to endometriosis [5], and the literature is scarce on the

topic. Considering the potential risk of neoplastic transformation associated with EAI, this

article aims to raise awareness among both gynecologists, who are frequently faced with the

diagnosis of endometriosis, and dermatologists, who may encounter EAI lesions, as well as

among patients themselves, to help identify and prevent harmful, extreme behaviors driven

by intense pain. This manuscript provides a literature review on the subject alongside a

clinical case from our practice.

2. Materials and Methods

A comprehensive literature search was carried out using PubMed (MEDLINE), Scopus,

and Google Scholar to explore the clinical and pathophysiological intersections between

EAI and endometriosis. The search strategy combined the following key terms and their

variations: “erythema ab igne”, “hot water bottle rash”, “toasted skin syndrome”, “endometriosis”, “dysmenorrhea”, “dyspareunia”, “behavior”, and “chronic pelvic pain.”

Boolean operators (AND/OR) were applied to capture studies linking heat-related skin

changes with gynecological pain syndromes. The search covered the period from January

1992 to 31 July 2025, which represents the date of the last update.

Eligible sources were peer-reviewed articles published in English that discussed

erythema ab igne or related cutaneous effects of heat, endometriosis and its associated pain

syndromes, behavioral coping strategies such as heat therapy, or relevant psychological and

dermatological aspects. We excluded non-peer-reviewed publications, such as conference

abstracts without full text, editorials, or letters lacking clinical data, as well as articles not

available in English or papers unrelated to either endometriosis or EAI.

The available literature proved to be extremely scarce. This limitation made a systematic methodology unfeasible, and therefore, the work was structured as a narrative review,

complemented by the presentation of a representative clinical case. No formal quality

assessment tool was applied, but priority was given to studies published in peer-reviewed

journals, clinical guidelines from professional societies, and recent high-quality reviews

whenever possible.

3. Results

3.1. EAI—Definition and Etiopathogenesis

EAI is a benign skin rash characterized by asymptomatic, reticulated, brown macules

caused by chronic exposure to external heat sources, below the skin burn threshold [1]. The

duration between heat exposure and EAI is largely variable (weeks to years). EAI is more

Life 2025, 15, 1533 3 of 14

frequent in women, with a 10:1 sex ratio. The average age of EAI is 28.6 +/− 10.4 years [1,6].

Radiant heaters (surface temperature usually 43–50 ◦C, depending on settings and distance),

laptops (surface temperature up to 40–47 ◦C, often modified by clothing acting as a barrier),

hot water bottles (typically 43–50 ◦C if applied directly, lower when wrapped in towels or

fabric covers), heating pads (typically 43–50 ◦C if applied directly, lower when wrapped

in towels or fabric covers), and heated car seats (typically 43–50 ◦C if applied directly,

lower when wrapped in towels or fabric covers) are frequently incriminated [7–9]. Recently,

virtual reality headset-induced EAI has been described [10]. EAI may be considered an

occupational dermatosis in glass blowers, jewelers, bakers, workers in the metallurgy

industry, chefs, and tandoor oven users [6,8,11].

EAI can sometimes point to an internal malignancy, as shown by Bunick et al., including pancreatic adenocarcinoma, gastric adenocarcinoma, colorectal adenocarcinoma,

hepatic metastases, spinal metastases, and lymphoma [12]. Hence, internal malignancies

should be ruled out in any patient with CPP and EAI.

3.2. Clinical Appearance and Differentials of EAI

EAI initially presents as a transitory erythema and later progresses into a brown,

reticular pattern with telangiectasias [9]. The most important differential diagnosis of

EAI is livedo reticularis (LR). LR is classified into physiologic LR (livedo marmorata) and

pathologic LR. Livedo marmorata represents a normal vasospastic response, appearing

upon cold exposure and disappearing upon local warming. In contrast, pathologic LR

is persistent [13].

Table 1 outlines the main differential diagnoses of EAI, including conditions associated with pathologic LR [6,13–16]. Rare forms of bullous EAI have been described in

patients with diabetes mellitus, anemia, eating disorders, and hypothyroidism. In this case,

bullous diseases, such as bullous pemphigoid and bullous lupus erythematosus, should be

ruled out [6].

Table 1. Differential diagnoses of erythema ab igne (EAI).

Etiology Conditions

Hematologic/Hypercoagulability disorder

Antiphospholipid antibody syndrome

Cryopathies (cryoglobulinemia, cryofibrinogenemia, cold agglutinins)

Polycythemia vera

Essential thrombocytosis

Protein C and protein S deficiency

Deep venous thrombosis

Thrombocytopathy

Autoimmune diseases/vasculitis

SLE

Rheumatoid arthritis

Sjogren’s syndrome

Dermatomyositis

Still’s disease

Sharp’s syndrome

Small and medium vessel vasculitis

Polyarteritis nodosa

Fibromyalgia

Vessel wall disorders/emboli

Calciphylaxis

Septic emboli, cholesterol emboli

Atrial myxoma

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Table 1. Cont.

Etiology Conditions

Infections

Hepatitis C

Mycoplasma pneumonia

Brucella, Rickettsia

Tuberculosis

Meningococcemia

Syphilis

Endocarditis

SARS-CoV-2

Parvovirus B-19

Neurological disorders

Diabetic neuropathy

Parkinson’s disease

Stroke

Multiple sclerosis

Migraine

Reflex sympathetic dystrophy

Neoplasia Renal cell carcinoma

Metastatic breast cancer

Lymphoma/leukemia

Mycosis fungoides

Angiotrophic lymphoma

Acute lymphocytic leukemia

Chronic natural killer cell leukemia

Multiple myeloma

Medications

Amantadine

Minocycline

Gemcitabine

Presors (ergotamine, cocaine)

Interferons (alpha and beta)

Heparin

Combination of antiretroviral (lopinavir) and antipsychotics

(aripiprazole)

Others

Anorexia nervosa

Physical abuse

Chronic pancreatitis

Homocysteinuria

Poikiloderma atrophicans vascularis

Panniculitis

3.3. Pathology of EAI

Since the pigmented, lacy pattern lesions signify local venous congestion, and the

white, central area is represented by inflamed or obstructed arterioles, the skin fragment

should always be obtained from the central area and not from the rings themselves [13].

The exact pathophysiology of EAI is unknown, but pathology samples display both epidermal and dermal alterations. In the early stages of EAI, the epidermis is atrophic, with

scarce atypical keratinocytes; vasodilatation, perivascular inflammation, and hemosiderin

deposits are seen in the dermis. In mature EAI lesions, the epidermis displays dyskeratosis, focal parakeratosis, and vacuolization. Still, the usual histopathology findings are

nonspecific and exclude other diagnoses [6,17].

A subepidermal blister is encountered in bullous EAI. Direct immunofluorescence

(DIF) should be performed to exclude other subepidermal bullous disorders. In the setting

of a non-concluding pathology report, DIF may also exclude vasculitis (Table 2) [18,19].

Life 2025, 15, 1533 5 of 14

Table 2. Direct immunofluorescence (DIF) differential diagnoses of bullous EAI.

Etiology Direct Immunofluorescence (DIF)

Pemphigus vulgaris Intercellular space deposits of C3, IgG (chicken wire pattern)

Pemphigus paraneoplastic Intercellular space and basement membrane zone deposits of C3, IgG

Bullous Pemphigoid Basement membrane zone linear deposits of C3 > IgG

Bullous lupus erythematosus Granular and/or linear deposits of IgG and C3 +/− IgA or IgM along the basement

membrane zone (lupus band)

Dermatitis herpetiformis Granular IgA deposits along the basement membrane zone and within dermal papillae

Leukocytoclastic vasculitis Granular/fibrillar deposits of IgA > IgG/IgM, C3, or fibrinogen within the walls of

superficial small vessels

Bullous erythema ab igne Negative

3.4. EAI-Associated Malignization

Later stages of EAI can demonstrate increased dyskeratosis and dermal elastosis

and pose the risk of malignant transformation [20]. Unlike the intensely studied UV

radiation, the biological effects of infrared radiation (IRR) on human skin are less studied.

The carcinogenic effect of IRR was described by decreasing keratinocyte apoptosis and

promoting proliferation via heat shock proteins (HSPs). Temperatures above 39 ◦C (heat

shock), but below 45 ◦C, trigger the activation of HSPs, intracellular and ubiquitary proteins

responsible for the correct folding and transport of other proteins, as well as the reassembly

of proteins that have been misfolded as a result of heat stress [21,22].

The heat shock response consists of trimerization and phosphorylation of heat shock

factor (HSF), which translocates into the nucleus and promotes the expression of HSPs

(especially HSP70 and HSP92). HSPs determine defective DNA replication, transcription,

and repair. HSPs activate NRAS and BRAF kinases and promote keratinocyte proliferation.

Additionally, it inhibits the keratinocytes’ apoptosis by down-regulating death signaling

pathways, such as the p53 protein and c-Jun NH2 terminal kinase (JNK) [21–25].

Hence, although EAI is a benign skin condition, it may eventually evolve into a

squamous cell carcinoma (SCC), Merkel cell carcinoma, or even basal cell carcinoma (BCC)

(Figure 1). For this particular reason, a long-term dermatological follow-up is generally

recommended in EAI patients, and any ulceration should be promptly biopsied [6,26], as it

may represent a Marjolin ulcer. Marjolin ulcer represents an aggressive SCC arising within

a preexisting skin disorder, usually chronic inflammation or scarring [27].

Figure 1. Skin cancers (BCC, SCC, Merkel cell carcinoma) in EAI induced by infrared radiation (IRR).

The heat shock response inhibits apoptosis (via JNK and p53) and stimulates cell proliferation via the

NRAS/BRAF/MEK/ERK pathway.

Life 2025, 15, 1533 6 of 14

3.5. EAI Treatment

The first-line treatment for EAI is the elimination of the IRR source. However, the

reticular, hyperpigmented pattern may persist indefinitely or slowly fade [6]. Topical

treatments such as hydroquinone and retinoids can help improve the appearance of the

skin. Additionally, the application of 5-fluorouracil (5-FU) and imiquimod may be beneficial

if keratinocyte dysplasia is present [28–30].

Kim et al. obtained good cosmetic results using a 1064 nm low-fluence Q-switched

Neodymium-Doped Yttrium Aluminum Garnet (QS Nd-YAG) laser at weekly intervals in a patient with EAI and no evidence of dysplasia [31]. SCC secondary to EAI

should be surgically excised, and the patients may benefit from a Mohs micrographic

surgery approach [32].

3.6. Endometriosis-Related EAI

Dysmenorrhea is the central clinical feature of endometriosis. However, it is divided into primary dysmenorrhea, which occurs in the first 6–12 months after menarche, and secondary dysmenorrhea, which occurs 12 months after menarche [33]. It is

estimated that dysmenorrhea affects around 70–93% of women [34]. The pain mechanism occurs through increased production of prostaglandins, leukotrienes, and vasopressin, which induce increased myometrial contractility and vasoconstriction, resulting in

endometrial ischemia [35–37].

Endometriosis and adenomyosis are the main causes of secondary dysmenorrhea,

which gradually transforms into acyclic pain and chronic pelvic pain [35,38]. Endometriosis

often causes symptoms that fluctuate with the menstrual cycle, varying from mild to severe.

These can include pain in the abdomen, lumbosacral region, perineum, buttocks, rectum,

and vulvovaginal area [39]. Some patients may also experience weakness, dyspareunia,

and loss of bladder or bowel control [40]. When the central or peripheral nervous system

is involved, neurological symptoms such as leg and pelvic pain, cyclic radiculopathy of

the lower limbs, urinary incontinence, and, in rare cases, paraplegia can occur [41]. Nerve

involvement plays a key role in endometriosis-related pain. Ectopic endometrial tissue can

irritate or invade peripheral nerves, triggering pain [42].

Neuroangiogenesis (new blood vessel growth around nerves) promotes inflammation

and nerve activation, contributing to perineural invasion [43]. Both peripheral and central

sensitization occur, heightening pain perception. Additionally, adhesions may compress

nerves, causing sharp, persistent pain and hyperalgesia [44]. Severe pain often suggests

direct nerve involvement. Endometriosis can also present with gastrointestinal and urinary

symptoms like constipation, diarrhea, or dysuria, which may complicate diagnosis [45,46].

These factors underscore the complex pain pathways involved and the importance of

multidisciplinary care.

Common CPP causes include inflammatory bowel disease, nerve entrapment, adenomyosis, endometriosis, adhesions, cystitis, internal malignancies, chronic endometritis,

vulvodynia, and musculoskeletal etiologies. The Carnett test differentiates between visceral and abdominal wall pain. Additionally, depression and trauma history should be

carefully investigated [47].

Heating pads alleviate pain among 29.5% of patients who experience CPP [48].

A Canadian study showed that alternative therapies, especially heat and cannabis, are

commonly used by patients with endometriosis [49]. Women with endometriosis use an

average of 5.8 self-care interventions more than once a week, including heat, rest, over-thecounter pain medications, and diet changes [50]. However, according to the 2022 ESHRE

Guidelines, no recommendations can be made regarding non-medical interventions to

Life 2025, 15, 1533 7 of 14

reduce pain, including nutrition, electrotherapy, acupuncture, physiotherapy, exercise, and

psychological interventions [8].

CPP is increasingly recognized as more than a physical disorder, as its persistence

induces neuroplastic changes in the central nervous system that predispose to psychiatric

comorbidities, particularly within the anxiety–depressive spectrum [51]. Primary dysmenorrhea has been associated with a 1.7-fold increased risk of depressive disorders [52], and

women with CPP, often overlapping with endometriosis, show high rates of anxiety and

depression (up to 48%), closely related to pain severity rather than disease stage [53,54].

Systematic reviews confirm that chronic visceral pain almost invariably coexists with

psychiatric symptoms [55,56]. These psychological burdens may encourage maladaptive

coping behaviors, including the excessive use of heat therapy, which underscores the importance of integrating dermatologic risk awareness and patient education into comprehensive

pain management.

Regarding the alleviation of dysmenorrhea, it is essential to understand and educate

patients on the appropriate and safe use of heat-based devices specifically designed for

this purpose. While local heat application is known to provide significant symptomatic

relief by improving pelvic blood flow, reducing uterine contractility, and modulating pain

perception, it is not without potential risks. Prolonged or inappropriate use of heating pads

can lead to skin burns or chronic thermal injury, including EAI. This is particularly relevant

in patients with endometriosis, who often rely on long-term and recurrent heat therapy due

to persistent pelvic pain. Misuse of such devices may not only provoke skin damage but also

delay medical consultation or mask the progression of underlying disease. Unfortunately,

some publications extrapolate data from clinical studies and oversimplify it in public-facing

articles, claiming that heat application has no adverse health consequences [57].

This is misleading, as the cited studies typically use heat therapy in a strictly controlled

setting, standardized in terms of temperature, duration, and application method, often

within randomized controlled trials designed to assess short-term analgesic efficacy [58,59].

Translating these findings into blanket statements for general use, without discussing safety

parameters, may encourage inappropriate or excessive use, particularly in vulnerable

populations such as women with endometriosis.

The management of EAI in patients with endometriosis does not differ from standard treatment protocols. However, the chronic nature of EAI and the patient’s frequent

willingness to conceive following DE surgery may complicate the management of EAI in

newly pregnant patients. In this context, topical therapies with hydroquinone, retinoids,

imiquimod, and 5-FU are generally not recommended [60], and a wait-and-see attitude

is preferable.

Given the strong link between chronic pelvic pain, maladaptive coping behaviors such

as excessive heat use, and the risk of EAI, we propose a practical clinical algorithm for

screening and management (Table 3).

Table 3. Clinical algorithm for screening and management of EAI in endometriosis patients.

Screening and clinical

suspicion Identify patients at risk

- Endometriosis/CPP patients using heating devices

(hot water bottles, pads, heated seats)

- History: device type, temperature, frequency, barriers

(clothing/towel)

- Assess coping behaviors, pain severity, psychiatric

comorbidities

- Physical exam: reticulated brown

macules/telangiectasias; urgent referral if ulcerated

Life 2025, 15, 1533 8 of 14

Table 3. Cont.

Diagnostic work-up Confirm diagnosis and rule

out differentials

- Clinical diagnosis in typical cases

- Biopsy from central lesion if

atypical/ulcerated/non-healing

- DIF (if bullous) to exclude autoimmune blistering

- Laboratory/imaging if suspected vasculitis/internal

malignancy

Management General, dermatologic, and

gynecologic care

a. General:

- Eliminate/reduce heat exposure

- Psychological support for coping

b. Dermatologic:

- Hydroquinone, retinoids for pigmentation (not

in pregnancy)

- 5-FU or imiquimod if dysplasia

- Q-switched Nd-YAG laser for persistent lesions

Surgical excision/Mohs if malignant

c. Gynecologic/Pain:

- Optimize endometriosis treatment

(hormonal/surgical)

- Non-thermal coping: medication,

physiotherapy, cognitive behavioral

therapy, lifestyle

Follow-up Ongoing multidisciplinary

care

- Dermatology: every 6–12 months, earlier if ulceration

- Gynecology: ensure pain control to prevent

maladaptive heat use

- Psychological: address anxiety/depression, reinforce

safe coping

3.7. Evidence Gaps

Current knowledge on EAI in endometriosis is limited. The prevalence of EAI in this

population remains unreported, and the overall cancer risk is undefined and based only on

low-level evidence. No standardized safety recommendations exist for the use of home

heat devices in chronic pelvic pain. Addressing these gaps requires larger observational

studies and the development of clear safety guidelines.

4. Case Presentation

A 33-year-old nulliparous Caucasian woman was referred with a prolonged history of

diffuse abdominal and pelvic pain, dysmenorrhea, and deep dyspareunia. She described

dysmenorrhea beginning at the age of 18 years old, approximately four years after the

menarche, with a progressive worsening over the past decade. Two years before presentation, she developed CPP with a distinct cyclical pattern: discomfort commenced around

the time of ovulation and progressively worsened until the onset of menstruation, during

which it peaked in intensity. The pain was described as dull, bilateral, and cramp-like,

often radiating to the lower back and inner thighs. Despite regular use of NSAIDs, symptomatic relief was inconsistent, and due to the refractory nature of her symptoms, the

patient adopted extreme thermal measures, including frequent hot showers and continuous

application of heating pads, particularly during menstruation.

She also reported deep dyspareunia with penetrative intercourse, which significantly

impacted her sexual activity and quality of life. She denied gastrointestinal and urinary

symptoms, including dyschezia or hematuria, and had no prior history of pelvic inflamma-

Life 2025, 15, 1533 9 of 14

tory disease or surgery. Her menstrual cycles were regular (28–30 days) and lasted approximately 5–6 days. She had been using barrier contraception and never tried to conceive.

There was no significant family history of endometriosis or gynecologic malignancies.

The clinical examination revealed diffuse, reticulated hyperpigmentation of the lower

abdomen and upper thighs concerning livedo reticularis. Nodules and ulcerations were

absent (Figure 2). The skin rash was not symptomatic. She first noticed the eruption

10 months before hospital admission, concomitant with the use of heating pads, with a

distribution corresponding to the heating devices. The patient used the heating pads for

4 to 5 h daily and sometimes during nighttime sleep.

Figure 2. Reticular, brown, symmetric macular exanthema involving the anterior lower abdomen

and superior thighs.

The patient underwent a gynecological evaluation and a pelvic ultrasound with a

suspected diagnosis of DE. Abdominal palpation revealed mild tenderness in the lower

abdomen. Pelvic examination demonstrated uterine tenderness with limited mobility and

nodularity along the uterosacral ligaments. Pain was reproduced upon deep vaginal palpation and cervical motion. A transvaginal ultrasound (TVUS) examination demonstrated a

subtle hypoechoic area along the uterosacral ligaments. Furthermore, an irregular hypoechoic nodule with ill-defined margins was detected on the anterior rectal wall, indicative

of DE. The absence of a sliding sign between the posterior uterine wall and the anterior

rectum suggests the presence of adhesions and DE.

Pelvic MRI revealed diffuse adenomyosis. A conglomerate of multiple right ovarian

endometriomas (n = 7) was identified, the largest located on the posterior aspect of the

ovary. Four left ovarian endometriomas were described, with the largest situated at the

posterior pole; the remaining lesions were infracentrimetric. Bilateral superficial periovarian endometriotic implants were also noted. A deep endometriotic lesion involving

the posterior uterine wall was observed at the insertion of the uterosacral ligaments and

in the retrocervical region, adherent to the posterior vaginal fornix and the mid-rectum.

Life 2025, 15, 1533 10 of 14

Endometriotic infiltration was detected along the course of the uterosacral ligaments with

parametrial extension and bilateral ovarian adhesions, more pronounced on the right side.

A “kissing ovaries” appearance was present. Superficial infiltration of the mid-rectal wall

was described at the site of uterine adhesion, approximately 8 cm cranial to the anal verge,

without invasion of the muscularis propria. The pouch of Douglas appeared obliterated due

to an adhesive complex involving the uterus, rectum, and both ovaries.

Preoperatively, a screening for connective tissue disorders excluded systemic lupus

erythematosus, ANCA vasculitis, and anti-phospholipid antibody syndrome. The dermatology evaluation suspected EAI, given the patient’s exposure to external localized

heat. A 6 mm punch biopsy was performed to exclude differentials. The pathology report

revealed a thin epidermis, non-specific perivascular infiltrate (hematoxylin–eosin stain),

and fragmented elastic fibers (Van-Gieson stain), consistent with the diagnosis of EAI.

Laparoscopic surgical treatment included extensive pelvic adhesiolysis and restoration

of normal pelvic anatomy. Complete excision of endometriotic lesions was performed at the

level of the uterosacral ligaments, rectovaginal septum, and posterior vaginal fornix, and

a rectal shaving procedure was carried out. Bilateral ovarian cystectomy with excision of

endometriomas was performed. The postoperative #ENZIAN classification was A2B2C2FA,

indicating moderate-to-severe involvement of the retrocervical/vaginal compartment (A2),

uterosacral ligaments/parametrium (B2), and rectum (C2), along with bilateral ovarian

involvement and associated adenomyosis (F: ovaries and uterus) (Figures 3–5).

Figure 3. Intraoperative findings: (a). Bilateral ovarian endometriomas; (b). ovarian cystectomy.

Figure 4. Intraoperative findings: (a). left ureterolysis, excision of the left ovarian fossa peritoneum;

(b). Excision of the left uterosacral ligament.

Life 2025, 15, 1533 11 of 14

Figure 5. Intraoperative findings: (a). nodule of the rectovaginal septum and rectum; (b). rectal shaving.

The patient was advised to discontinue the heating pads, and the pigmentation ameliorated under hydroquinone and retinoid topical treatments. Abdominal and pelvic

pain, dysmenorrhea, and dyspareunia were solved postoperatively. Regular dermatology

follow-up was recommended for the patient.

5. Conclusions

While EAI remains a benign skin condition resulting from heat exposure, it possesses

the potential for neoplastic transformation by disrupting normal apoptotic processes and

promoting cell proliferation, thereby increasing the risk of non-melanoma skin cancers

(SCC, Merkel cell carcinoma, BCC). Differential diagnoses of EAI are complex, and although

the diagnosis is generally clinically based, a skin biopsy from the center of the ring will

certainly rule out differentials, such as LR or vasculitis. A bullous EAI should be examined

additionally with a DIF.

This review particularly emphasizes the vulnerable subgroup of patients suffering

from dysmenorrhea and chronic pain due to endometriosis, who frequently seek both conventional and alternative therapies for symptomatic relief. EAI in these patients represents

more than a dermatological condition: it symbolizes the severe pain that follows these

patients throughout their daily lives and their somatic disability.

As the recognition of endometriosis has grown over the past decade, it is crucial to

implement new preventive strategies, promote accurate dissemination of information, and

raise awareness about the risks associated with heat exposure. A more nuanced understanding of heating devices is required, combining patient education on safe usage with

a multidisciplinary approach to endometriosis-associated pain management. Healthcare

professionals, including gynecologists, dermatologists, and family physicians, must play an

active role in patient education, risk assessment, and management, ensuring that patients

receive care with the utmost respect and understanding of the potential dangers.

Author Contributions: Conceptualization, F.S., A.I.G.B., L.G.S. and C.M.; methodology, A.P. and

C.M.; software, F.S., A.I.G.B., L.G.S. and C.M.; formal analysis, F.S.; investigation, F.S., L.G.S. and

A.I.G.B.; writing—original draft preparation, F.S., L.G.S. and A.I.G.B.; writing—review and editing,

C.M. and A.P.; visualization, L.G.S. and F.S.; supervision, A.P. and C.M. All authors have read and

agreed to the published version of the manuscript.

Funding: This research received no external funding.

Institutional Review Board Statement: Not applicable.

Informed Consent Statement: Written informed consent has been obtained from the patient to

publish this paper.

Data Availability Statement: No new data were created or analyzed in this study.

Acknowledgments: Publication of this paper was supported by the University of Medicine and

Pharmacy Carol Davila, through the institutional program Publish not Perish.

Life 2025, 15, 1533 12 of 14

Conflicts of Interest: The authors declare no conflicts of interest.

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