. Hives lasting less than six weeks are called "acute urticaria." With this type of hives, the cause can usually be found. . The most common causes are foods, drugs, or infections. . Insect bites and internal disease may also be responsible. . Other causes can be pressure, cold, or sunlight.

. Foods

. The most common foods that cause hives are nuts, chocolate, fish, tomatoes, eggs, fresh berries, and milk. . Fresh foods cause hives more often than cooked foods. . Food additives and preservatives may also cause hives.

. Hives may appear within minutes or up to two hours after eating, depending on where the food is absorbed in the digestive tract.

. Drugs

. Almost any prescription or over-the-counter medication can cause hives. . Some of those drugs include antibiotics, pain medications, sedatives, tranquilizers, and diuretics (fluid pills). Diet supplements, antacids, arthritis medication, vitamins, eye drops and eardrops, laxatives, vaginal douches, or any other non-prescription item can be a potential cause of hives. If you have an attack of hives, it's important to tell your doctor about all of the preparations that you use to assist in finding the cause.

. Infections

. Many infections can cause hives. . Colds are a common cause of hives in children.

. Chronic Urticaria

Hives lasting more than six weeks are called "chronic urticaria." The cause of this type of hives is usually much more difficult to identify than that of acute urticaria. . In patients with chronic urticaria, the cause is found in only a small number of patients. . Your doctor will need to ask many questions in an attempt to find the possible cause. Since there are no specific tests for hives, testing will depend on your medical history and a thorough examination by your dermatologist.

. Physical Urticarias

. Hives can be caused by sunlight, heat, cold, pressure, vibration, or exercise. . Hives due to sunlight are called solar urticaria. This is a rare disorder in which hives form on exposed areas within minutes of sun exposure and fade within one to two hours. . Hives due to the cold are more common. . These appear when the skin is warmed after exposure to cold. . If the cold has affected large areas of the body, large amounts of histamine may be released, which can produce wheezing, flushing, generalized hives, and fainting.

. Dermatographic Urticaria

. Hives that form after firmly stroking or scratching the skin are called "dermatographism." This affects about 5 percent of the population. . Most people with this condition are otherwise healthy. . These hives can also occur along with other forms of urticaria. . They may typically appear in young women and last for months or even years.

Tratamiento

. The best treatment for hives is to find and remove the cause. . This is not an easy task and may not even be possible. . Antihistamines are usually prescribed by your dermatologist to provide relief. . Antihistamines work best if taken on a regular schedule to prevent hives from forming. . No one antihistamine works best for everyone, so your dermatologist may need to try more than one or several different combinations to find what works best for you. . In severe hives, an injection of epinephrine (adrenalin) or a cortisone medication may be needed.