Hives, also called urticaria, appear as itchy, red welts on the surface of the skin and are usually caused by an allergic reaction. Hives in adults start suddenly and go away quickly, can vary in size, appear anywhere on the body, and can move around on the body throughout the course of the reaction.
When the body encounters an allergic substance it releases histamine and other chemicals into the bloodstream. The histamine causes itching, swelling, and even hives. Hives start out as a swelling of the surface of the skin that turns into red- or skin-colored welts with clearly defined edges. Hives cause discomfort but prove harmless and usually go away in less than 24 hours. However, severe cases of hives may lead to anaphylactic shock, which consists of a whole-body allergic reaction, that causes a difficulty in breathing or swallowing, and requires emergency care.
Foods that commonly cause hives include nuts, chocolate, shellfish, tomatoes, eggs, berries, and milk. Food additives and preservatives also cause hives. Hives caused by food allergies appear within minutes to several hours after eating. The appearance of symptoms depends upon the site within the digestive tract that absorbs the food.
The American Academy of Dermatology, also known as AAD, reports that an allergic reaction can occur in adults from almost any medication--including over-the-counter medications.
Infections such as mononucleosis, viral infections, and illnesses including lupus, other autoimmune diseases and leukemia cause the development of hives.
Natural causes of hives include sunlight, heat, extreme cold, water, pressure, vibration, and excessive perspiration that can occur with exercise. Hives form within minutes of sun exposure and typically fade within one to two hours.
Scratching the Skin
Dermatographic hives, also called dermatographism, form after a person firmly strokes or scratches the skin, and often happen with other forms of hives. Dermatographism occurs in healthy adults, and the condition can last for months or even years.
According to the American Academy of Allergy Asthma and Immunology, stress causes chronic hives in some adults. This condition can occur almost daily for months or, in some cases, years. An allergist or immunologist can diagnosis the problem and prescribe treatments for this bothersome condition.