Heat Rash Medical Terminology
The medical term for skin rash caused by heat is "cholinergic urticaria" when triggered by elevated core temperature and sweating, or "localized heat urticaria" when caused by direct heat contact. 1
Classification of Heat-Induced Skin Conditions
The British Association of Dermatologists classifies thermal urticarias as a subset of physical urticarias, which are reproducibly induced by specific physical stimuli 1:
Thermal Urticarias Include:
Cholinergic urticaria: Primarily induced by stimuli that trigger sweating rather than overheating itself, though elevated core temperature is the usual reason for sweating 1
Localized heat urticaria: Triggered by direct application of heat to the skin 1
Cold contact urticaria: The opposite thermal trigger (included for completeness of thermal spectrum) 1
Key Distinguishing Features
Physical urticarias produce induced rather than spontaneous swellings, with weals typically lasting less than one hour except in delayed pressure urticaria 1. This distinguishes them from ordinary urticaria where weals last 2-24 hours 1.
Clinical Characteristics:
- Weals are reproducibly triggered by the same physical stimulus 1
- Heat or pressure from clothing can aggravate urticarial lesions 1
- Defining the specific stimulus allows for lifestyle modifications to minimize or prevent episodes 1
Important Caveat
Do not confuse heat-induced urticaria with "erythema ab igne" (also called "toasted skin syndrome"), which is a completely different condition caused by chronic, prolonged exposure to infrared radiation or moderate heat sources 2, 3, 4. Erythema ab igne presents as a reticulated, hyperpigmented rash rather than transient weals, and results from repeated heat exposure over weeks to months 3, 5.