, or urticaria, are an extremely common skin rash, characterized by patches of raised, reddened, and itchy skin which typically come and go over a large part of the body. Hives are caused by the activation of histamine-releasing cells in the skin, and they are typically thought of as signifying an allergic reaction.
This is certainly true for many people. For example, people with food allergies or contact allergies will often break out in hives when they come in contact with the allergens. However, just as common is a transient case of the hives associated with certain upper respiratory tract infections and other common viral infections. These hives tend to go away as the infection clears up.
Generally speaking, hives are not a harmful process. In the case of an allergic reaction, they are concerning only if other allergy symptoms emerge, such as swelling of the lips, tongue, or face, or wheezing or trouble breathing. If you experience any of these symptoms, you need to seek emergency medical care immediately.
Isolated cases of hives can usually be managed with over the counter Benadryl or some other antihistamine medication. If they don't clear up within a few days you can talk to your primary care doctor