•Foods (commonly eggs, shellfish, nuts, berries, dyes, or other additives)
•Drugs (any drug can touch off an allergic reaction, although allergies to penicillin, sulfa, and aspirin
are especially common)
•Pollens and plants (nettles, poison ivy, poison oak, and so on)
•Insect bites or stings
•Exposure to heat, cold, or sunshine.
Comfort is the main goal of treatment, since most hive outbreaks are relatively minor and short-lived.