Erythema ab igne https://en.wikipedia.org/wiki/Erythema_ab_igne
Erythema ab igne is a skin condition caused by long‑term exposure to heat (infrared radiation). Prolonged thermal radiation to the skin can lead to reticulated erythema, hyperpigmentation, scaling, and telangiectasias in the affected area. Some individuals may experience mild itchiness and a burning sensation.

Various heat sources can cause this condition, including:
- Repeated use of hot water bottles, heating blankets, or heat pads for chronic pain relief.
- Repeated exposure to heated car seats, space heaters, or fireplaces. Prolonged exposure to a heater is a common cause in elderly individuals.
- Occupational hazards for silversmiths and jewellers (face exposed to heat), bakers and chefs (arms, face).
- Resting a laptop computer on the thigh (laptop‑induced erythema ab igne).

More information ― English
References Erythema Ab Igne 30855838 
NIH
Erythema ab igne is a rash characterized by a reticulated pattern of erythema and hyperpigmentation. It is caused by repeated exposure to direct heat or infrared radiation, often from occupational exposure or the use of heating pads. The primary treatment of this disease entity is the removal of the offending heat source. The resulting abnormal pigmentation of affected areas may resolve over months to years; however, permanent hyperpigmentation or scarring may persist. Treatments for hyperpigmentation, such as topical tretinoin or hydroquinone, can be useful in treating persistent hyperpigmentation.