An allergy is a reaction by your immune system to something that does not bother other people. People who have allergies often are sensitive to more than one thing. Normally, your immune system fights germs. It is your body’s defense system. In most allergic reactions, however, it is responding to a false alarm. Genes and the environment probably both play a role.
According to the leading experts in allergy, an allergic reaction begins in the immune system. Our immune system protects us from invading organisms that can cause illness. If you have an allergy, your immune system mistakes a harmless substance as an invader. This substance is called an allergen.
The prevalence of allergic diseases such as allergic rhinitis and bronchi asthma has increased in recent years. Air pollutants can modify and enhance the allergic response in susceptible individuals.