Hives, also called urticaria, are areas of red, raised skin that often appear suddenly and spread fast. These bumps or welt are often itchy and uncomfortable. This condition is also known as nettle rash.
A serious outbreak on your skin can look scary, especially if it is your first, but is usually nothing to worry about. Hives may appear quickly, covering a large area of your skin, and be gone in a few hours. The bumps often move around and may clear up temporarily, only to come back later in a few hours. It may or may not be accompanied by swelling, known as angioedema. One outbreak does not typically exceed 24 hours.  If you have multiple outbreaks at different times of the day, it may take longer.
Although the cause of hives is not always known, most are triggered by allergens. Allergens trigger the release of histamine and other chemicals into the bloodstream. When histamine enters the bloodstream, small capillaries may leak fluid that accumulates in the skin and cause rashes. 
According to the American College of Allergy, Asthma and Immunology (ACAAI), hives affect up to 20 percent of people at some point in their lives.  These are some common causes:
Hives may appear on your skin when you eat certain foods. If you have had urticaria before or frequently suffer from it, you should be careful about the kinds of foods you consume. Not everyone has the same food triggers, so what triggers this reaction in someone else may do nothing to you. Pay attention to which foods trigger you to have these symptoms and those that do not. You can keep a journal of foods that trigger this reaction and avoid them. While food triggers differ for everyone, some foods are more likely to do this. According to the American College of Allergy, Asthma and Immunology (ACAAI) , foods you should look out for include eggs, nuts, and shellfish. Tomatoes, fish, milk, fresh berries, and chocolate may also trigger hives.  Uncooked foods and certain food additives are more likely than cooked foods to cause urticaria.