Histamine is a chemical released from specialized cells along the skin's blood vessels. Allergic reactions
, chemicals in foods, insect stings, sunlight exposure, or medicines can all cause histamine release. Sometimes it's impossible to find out exactly why hives have formed.
The most common foods that cause hives are nuts, chocolate, fish, tomatoes, eggs, fresh berries, and milk. Certain food additives and preservatives may also be to blame.