Hi,
Itchy bumps which keep appearing are usually due to an allergy.When an irritant comes into contact with your body, your immune system sends chemicals, including histamine, to fight it. The sudden spike in histamine levels can cause an outbreak in the upper layers of the skin.
Common triggers are:
•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)
•Animal fur
•Insect bites or stings
Treatment is with anti-histamines like Cetrizine/Loratidine etc. You can also apply Calamine lotion on the affected areas.
The reason for the reaction is genetically determined.
ref:http://www.myonlinewellness.com/topic/hivestreatment