Urticaria, also as hives, is an outbreak of swollen, pale red bumps or plaques (wheals) on the skin that appear suddenly - either as a result of the body's to certain allergens, or for unknown reasons.
Hives usually cause itching, but may also burn or sting. They can anywhere on the body, including the face, lips, tongue, throat, or ears. Hives vary in (from a pencil eraser to a dinner plate), and may join together to form larger areas known as plaques. They can for hours, or up to one day before fading.
Angioedema is similar to hives, but the swelling occurs beneath the skin instead of on the . Angioedema is characterized by deep swelling around the eyes and lips and sometimes of the genitals, hands, and feet. It generally lasts longer than hives, but the swelling usually goes in less than 24 hours.
Rarely, angioedema of the throat, tongue, or lungs can block the airways, causing breathing. This may become life threatening.
Allergic hives and angioedema form when, in response to histamine, blood plasma leaks out of small blood in the skin. Histamine is a chemical released from specialized cells along the skin's blood vessels.
Allergic reactions, chemicals in certain foods, stings, sunlight exposure, or medications can all cause histamine release. It's often impossible to out exactly why hives have formed.
There are several different types of hives, including:
Acute urticaria: Hives lasting than six weeks. The most causes are certain foods, medications, or infections. Insect bites and internal disease may be responsible.
Chronic urticaria and angioedema: Hives lasting more than six weeks. For most people with chronic urticaria, the cause is impossible to . In some cases, though, the cause may be thyroid disease, hepatitis, infection, or cancer.