"Thermal allergy" is a general term that may used---but rarely is employed---in a discussion of allergic reactions to exposure to heat or cold. The term has largely if not entirely disappeared from the lexicon of allergy research as well as from allergy clinics. Websites of highly respected centres of scientific research with a focus on allergies, including that of Johns Hopkins University's Division of Allergy and Clinical Immunology, bear no trace of "thermal allergy."
More common experiences---or terminology describing them---include sun allergy, heat allergy and cold allergy, also called "cold urticaria."
Symptoms of allergic reactions to exposure to sun or heat include flushed skin and skin rashes. Children and the elderly are particularly vulnerable. The rashes are often itchy and affect areas that have been exposed to the sun or heat. While wearing sunscreen may help protect your skin from sun damage, an allergic reaction is still possible when your skin is exposed to direct sunlight.
Cold urticaria is sometimes called "cold hives," according to the Mayo Clinic website, which lists symptoms as redness, itching, swelling and hives on the skin following exposure to cold temperatures.
An extreme reaction, the website notes, is "a severe, whole-body reaction---leading to fainting, shock and even death."
The initial step of treatment of allergic reactions to temperature extremes is relatively easy. As soon as you notice symptoms, seek a friendlier environment. Treatment for mild rashes and skin irritations caused by such allergies are available over the counter. Topical creams, such as hydrocortisone, are effective at reducing redness and discomfort. Over-the-counter histamine blockers may also relieve symptoms.
Despite the easy availability of such products, however, self-treatment based on self-diagnosis carries its own set of risks. Proper diagnosis, management and treatment of any allergy requires consultation with a physician, who may refer the patient to an allergy specialist.
Preventing allergic reactions to sunlight or temperature extremes normally is relatively easy: The less time you spend exposed to the direct rays of the sun or to very hot or very cold environments or circumstances, the less likely you are to have a reaction.
If you have very sensitive skin or if you wish to take extra precautions against exposure to the sun, treating the skin with moisturisers prior to going out and applying aloe vera when returning inside may help mitigate skin irritation. Be sure to drink plenty of fluids to keep your skin healthy and hydrated.
People with cold urticaria should avoid exposure to cold air as well as cold water, the Mayo Clinic advises.
Other Types of Temperature-Related Allergies
Skin rashes and irritation are the mildest forms of allergic reactions associated with heat or cold. More serious reactions include solar urticaria, hives or pimples that develop one to four days after sun exposure; actinic folliculitis, raised bumps that can be paler or redder than surrounding skin and which appear roughly six hours after sun exposure; and actinic prurigo, a painful and itchy rash that may look like eczema and last for months or even years before it fully fades.
Allergies to sun exposure most often are mild and usually clear up within a few hours, often without medication. Several conditions, however, are exacerbated by increased sun exposure. Allergic reactions are unpredictable and the severity of an outbreak depends on many factors, such as the individual, the length and severity of sun exposure, and existing medical conditions.
Being fully aware of your particular level of sensitivity and vulnerability and following the recommendations of your personal physician or allergist represents the best protection.