Allergies
Background
Allergy is an altered immune response to a substance which is eaten, inhaled or injected and which is harmless in most people. Substances (allergens) as diverse as pollen, penicillin and bee venom produce reactions which vary in severity from a mild rash or itching/sneezing to bronchial asthma and, occasionally severe, life-threatening anaphylactic shock (see entry, Anaphylaxis).