Physical urticaria, or hives, is an allergic reaction to environmental stimuli that results in a red, itchy rash and welts on the skin. Environmental factors that may lead to physical urticaria include exposure to water or sun, delayed pressure, cold temperatures, sweat, and skin writing. The hives and rash usually subside by themselves, so treatment is aimed at relieving the itching. Treatment may be oral or topical, over the counter or prescription; phototherapy is also used as a treatment.
Histamine is a chemical that is released in response to an allergy. It pools in certain areas and causes itchy welts and skin rash. Some people have an allergic reaction to certain environmental triggers. Exactly why this occurs is not clear.
Aquagenic urticaria is a rare type of physical urticaria in which exposure to water causes an allergic reaction. The water temperature does not appear to be a factor in rash development. Water can be cold, warm, or hot and still cause a reaction.
Another rare type of urticaria is caused by the sun. When someone has solar urticaria, she develops the itchy rash whenever her skin is exposed to sunlight. To avoid the rash and hives, a person with this condition must cover her skin whenever she is outdoors or refrain from going outside during the day.
Delayed pressure urticaria is caused when the skin has been subjected to pressure for a period of time. For instance, someone who has a tight waistband or seat belt that puts pressure on the skin may develop urticarial symptoms. This usually happens between four to six hours after the pressure has been removed. It is uncommon.
Cold-induced urticaria is also uncommon. When the skin is exposed to cold conditions, such as from the rain, wind, or snow, hives develop. Doctors are not certain if it is the cold that triggers this type of urticaria or if the trigger is the skin warming. The rash can be widespread or localized to one part of the body.
Cholinergic urticaria is triggered by sweat and produces very small welts, mostly on the trunk and arms. This condition is more common than the other types of urticaria. Some people become short of breath for the 30-60 minute duration of the rash. This condition often develops in early adulthood and may improve with age.
Dermatographic urticaria may occur when the skin is stroked or written on. A short-lived rash can develop along the lines of the writing or stroking. Sometimes this rash can be very itchy, but not always. About one in 20 people develop this condition, usually in early adulthood. As a person ages, she may experience fewer incidents of dermatographism.
There is no cure for any of these types of physical urticaria and treatment is symptomatic. Some individuals may find that oral antihistamines help the rash to fade more quickly and be less itchy. Antihistamines are available over the counter or with a prescription. Phototherapy treatment using ultraviolet light may help some people with physical urticaria, but hives are kept away for only a few months. Steroids, antifungal antibiotics, or tricyclic antidepressants may also be prescribed.
Topical treatments that contain camphor, menthol, diphenhydramine, and pramoxine may be purchased over the counter. These treatments work by deadening the nerve endings, which helps to reduce the intensity itching. According to some dermatologists, hydrocortisone or other cortisone-based lotions do not offer much help for physical uriticaria. Prevention and symptomatic treatment are generally the best ways to address physical urticaria.