An allergy is a specific reaction to a normally harmless substance, one that does not bother most people. Allergic people often are sensitive to more than one substance.
Allergens enter the body in one of three ways.
Medicines that can cause allergic reactions are injected or ingested. More than half of all allergy sufferers fails to recognize their symptoms at first, falsely believing they have a cold or the flu. Prevalence An estimated 50 to 60 million Americans. About one of every five adults and children suffer from allergies, including allergic asthma. Allergies are the sixth leading cause of chronic disease in the United States.