Overview of Hives
Hives, also called urticaria, are raised lesions that appear suddenly on the skin (called "wheals"). Hives usually are more or less round in shape and vary in size, up to several inches in diameter. They can appear anywhere on the body, as a single hive or in groups, and may be pink, red, or whitish in color.
Hives can disappear and then reappear, either in the same spot or in another area, and may last for hours, days, or even months or years. They may join together to form a larger skin rash and often are extremely itchy. Although hives are usually harmless and go away on their own within a few weeks, they may be a sign of a serious allergic reaction that requires immediate medical attention.
Types of Hives
Hives are classified in several different ways:
- Acute hives last fewer than 6 weeks and usually can be attributed to a specific cause.
- Chronic hives last longer than 6 weeks (sometimes months or years) and the cause may or may not be determined.
- Ordinary hives come on suddenly, for no apparent reason. They can disappear just as suddenly and then reappear elsewhere on the body, for days or weeks.
- Physical hives, which account for 15–20 percent of chronic hives, usually develop after direct contact with some aspect of the environment. Solar hives appear after sun exposure; cold hives appear when a person is warming up after spending time in the cold; and cholinergic urticaria causes hundreds of tiny bumps after intense exercise or a hot bath or shower. Other causes of physical hives include water, heat, vibration, and pressure on the skin (such as from a belt or clothing that is too tight).
- Dermatographic urticaria (dermatographism) occurs after the skin is scratched or rubbed. Sometimes this form of hives is called "skin writing" because the wheals appear in the same pattern as the scratch.
Incidence and Prevalence of Hives
It is estimated that between 10 and 20 percent of people develop at least one case of urticaria during their lifetime.