Hives

They are ‘reactions’ just below the skin and cause red itchy swellings. Many cases, but not all, are allergic. Common causes are chemical food additives, chemical sensitivities, and foods, the most common of which are: berries (including jams) citrus fruits (including marmalade), tomatoes, nuts, shellfish, and yeasts. Diagnostic diets and avoidance is the protocol here.

http://en.wikipedia.org/wiki/Urticaria