What cause hives and inflammation?

Allergic reactions: Hives & angioedema (deep tissue inflammation) are most often caused by things ingested (like foods & medicines), stinging insects, and latex allergy. They can also be caused by an underlying condition such as an autoimmune condition or blood disorder. Sometimes they result from direct physical activation of the skin such with exercise & cold. In many cases the cause is difficult to pinpoint.

Non-allergic hives: Most patients for whom a cause of hives is found are allergic to a food or medication.If hives last for over 6 wk (chronic hives) 80% are not allergic and no cause is found. In children and many adults viral infections, e.g. Colds, stimulate histamine release in the skin causing hives. Some patients have antibodies against the cells in the skin containing histamine, leading to histamine release.