Cholinergic urticaria

Cholinergic urticaria (CholU, CU) is a form of hives (urticaria) that is triggered by an elevation in body temperature, breaking a sweat, or exposure to heat. It is also sometimes called exercise-induced urticaria or heat hives. The condition is caused by an overreaction of the immune system to the release of histamine and other chemicals in response to the increase in body temperature. This results in the characteristic red, itchy, and sometimes raised bumps or welts on the skin that are associated with hives.

Cholinergic urticaria typically presents with a number of small papular hives all over the body, that involve cutaneous inflammation (wheals) and severe nerve pain, which usually develops in response to exercise, bathing, staying in a heated environment, spicy foods, or emotional stress. The symptoms subside and manifest rapidly on and off throughout the day with no notice. Cholinergic urticaria may significantly impair quality of life, especially in relation to normal day to day activities. It is caused by an overreaction of the immune system to the release of histamine, mast cells, and other chemicals in response to the small nerve fibers throughout the body due to the increase in body temperature being allergic to sweat.

This subtype of CU refers to those who are hypersensitive to their own sweat.

Diagnosis is made by injecting autologous (the person's own) sweat into the skin.

The hives are observed to coincide with perspiration points of sweating.

Tanaka et al. found that the sweat hyper-sensitivities of CU and atopic dermatitis seem to be virtually the same, and therefore, the sweat-induced histamine release from basophils may also be mediated by a specific IgE for sweat in atopic dermatitis as well as CU.

This subtype of CU refers to those who have abnormally reduced sweating. Forced perspiration by excessive body warming (hot bath or exercise) used daily may reduce the symptoms through exhaustion of inflammatory mediators.

Sweat is readily visualized by a topical indicator such as iodinated starch or sodium alizarin sulphonate. Both undergo a dramatic colour change when moistened by sweat. A thermoregulatory sweat test evaluates the body's response to a thermal stimulus by inducing sweating through the use of a hot box ⁄ room, thermal blanket or exercise. Failure of the topical indicator to undergo a colour change during thermoregulatory sweat testing can indicate anhidrosis and/or hypohidrosis (see Minor test).