They can vary in size from as small as a pencil eraser to as large as a dinner plate and may join together to form larger swellings. When hives are forming they usually are very itchy , but may also burn or sting. Hives are produced by blood plasma leaking through tiny gaps between the cells lining small blood vessels in the skin. A number of different things including allergic reactions , chemicals in foods or medications can cause a histamine release. Sometimes it's impossible to find out why histamine is being released and hives are forming.
Hives usually go away within a few days to a few weeks.
Occasionally, a person will continue to have hives for many years. When hives form around the eyes, lips or genitals, the tissue may swell excessively. Although frightening in appearance, the swelling usually goes away in less than 24 hours. Your dermatologist may use the term angioedema to describe this type of swelling. It's also used to describe very deep large hives on other areas of the body.