Erythema ab ignehttps://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 exposure to the skin can lead to the development of reticulated erythema, hyperpigmentation, scaling and telangiectasias in the affected area. Some people may complain of mild itchiness and a burning sensation.

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

  • Prolonged exposure to heat can cause this disorder.
  • This can happen if one's legs are exposed to a hot stove for a long time
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.