Updated May 27, 2011.

Urticaria, or hives, is a common skin condition that can affect up to 20% of the population at one time or another. Most people know that hives are very itchy, and anyone who's had hives knows the itching usually gets worse at night. This picture shows what a typical case of hives looks like. I don't know about you, but I want to scratch just looking at it.