Hives are a common allergic reaction, especially for those who already suffer from allergies. The rash appears as raised, itchy red welts on the surface of the skin. Hives can be triggered by animal dander, insect bites, medications, pollen, and foods such as shellfish, fish, nuts, chocolate, tomatoes, eggs and milk, according to Medline Plus. Reactions from emotional stress, extreme cold or sun exposure and excessive perspiration can also result in hives. Certain illnesses or infections may also make a person break out in hives.
Form
Hives, or urticaria, can last for a few hours, a day, a few days or weeks. Some people don't know how they got them or what caused the symptoms, which can include itching, swelling of the skin into red or skin-colored welts. The welts can form together and form larger areas of raised skin. The welts tend to disappear as fast as they appeared. Hives are uncomfortable, but they are usually harmless. In rare cases, the reaction may be severe if there are hives in the throat that can block a person's airway. This would require an emergency shot of adrenaline or steroids.
Tests
Because a hives episode may occur only once for many people, the cause remains unknown. This is not always the case for people who have a history of hives. Skin or blood tests can be performed to confirm a person has had an allergic reaction and tests might determine what caused the hives.
Episodes
About 10 to 20 percent of the population will have at least one episode of hives in their lifetime, according to the American Academy of Dermatology. Chronic urticaria can last more than six weeks in a small percentage of people. They may have to undergo extensive physical examinations and blood work to find the cause, which can by anything from heat and cold to water and exercise. Some people have episodes that pop up occasionally for months or years.
Reaction
People allergic to certain foods or food additives might see the hives appear within minutes after eating. The same fast reaction can occur in people allergic to certain substances. Almost any medication, prescription or over-the-counter product, can cause hives if the person is allergic to specific antibiotics, pain relievers, sedatives, supplements, antacids, vitamins and eye or ear drops. Infections that cause hives can stem from the common cold, strep throat, mononucleosis and hepatitis, according to the American College of Allergy, Asthma and Immunology.
Treatment
Avoid tight-fitting clothing and hot baths or showers to reduce the itching and swelling of hives. These activities can cause hives to return. If the hives do not go away after a day or so, check with a doctor for examination and treatment.
