Exposure to what substances causes hives?

Food, drugs, stings. Common causes of acute hives (hives lasting less than 6 weeks) are foods, medications and insect stings from honey bees, yellow jackets, hornets and wasps. Most common foods: peanuts, tree nuts, sesame, milk & any dairy product, egg, shellfish, fish, wheat, corn & soy. Most common drugs: antibiotics, aspirin, ibuprofen, naprosyn (naproxen).
Urticaria. Common triggers of hives (urticaria) include medications, foods, insect bites/stings or exposure to extreme weather. The cause of chronic urticaria is thought be related to a person's own immune system triggering the reaction. Some chronic urticaria can worsen with increased blood flow due to exertion, stress, alcohol, or fever. May be associated with h.Pylori, hepatitis or hyperthyroidism.