Can you be allergic to heat and sunlight, two things that Arizona has in extreme abundance? Unfortunately, the answer is yes.
Allergy to Heat
Normally, people do not break out in itchy hives when spending time in the sun or when exercising although people with chronic inducible urticaria (CIndU) might. In CIndU, hives and sometimes swelling occurs with exposure to a specific physical stimulus such as heat, cold, scratching, sunlight and even water.
CIndU caused by heat is also called cholinergic urticaria. People with cholinergic urticaria frequently have itching, redness, and small hives whenever there is an elevation in body temperature such as might occur with exercise, taking a hot bath, or sitting in a sauna. The rash can also be triggered by emotional stress or eating spicy and hot food. The trunk, arms, and legs are most frequently involved and the rash usually lasts from 15 minutes to an hour.
The diagnosis is usually apparent from the history but can be confirmed by an exercise challenge.
Treatment usually begins with non-sedating antihistamines such as Claritin, Allegra, Zyrtec or Xyzal. Antihistamines alone are frequently beneficial although it may take up to four times the usual dose to get things under control. More resistant cases have been treated with a variety of other medications including Xolair given by injection once a month.
Exercise-induced anaphylaxis is a more serious form of heat allergy. In this condition patients not only break out in hives but can have difficulty breathing and even lose consciousness from a drop in blood pressure with exercise. In some cases, the severe reaction to exercise only occurs if certain foods, such as wheat or peanut, are eaten before the activity. A careful exercise challenge can confirm the diagnosis and allergy testing can pinpoint the food allergy component. All patients with this condition should carry an EpiPen, never exercise alone, and strictly avoid food triggers before exercise.
Allergy to Sunlight
It sounds odd and certainly unfortunate if you live in Arizona, but some people will breakout with hives whenever their skin is in direct contact with sunlight for more than a few minutes. This condition is called solar urticaria.
The hives appear on sun-exposed skin several minutes after exposure to a specific wavelength of light and usually last for less than a day as long as you get out of the sun. Covering up to avoid direct contact with the sun is usually helpful although sunscreen, because it does not block the wavelengths of light causing the problem, is not. Phototesting can not only confirm the diagnosis
of solar urticaria but can identify the specific wavelengths of light causing the problem.
Sensitivity to sunlight can cause several other skin disorders called photodermatitis. These conditions, like solar urticaria, occur on sun exposed skin but typically last longer than 24 hrs.
The only thing worse than being allergic to sunlight and heat while living in Arizona is being allergic to dust – that is definitely a thing.