Allergies are reactions you have to otherwise harmless substances called allergens.
Normally, your immune system protects you against invading agents such as bacteria and viruses. If you have allergies, otherwise harmless allergens cause your body to react as if they were dangerous invaders. In effect, your immune system is responding to a false alarm.
The immune system thinks it is protecting you by generating large amounts of a type of antibody specific to the particular allergen you're allergic to.
This antibody attaches itself to certain cells in your body. The next time you come into contact with the allergen, the allergen attaches to the antibody like a key fitting into a lock. This “lock-up” causes the release of inflammatory substances into your system. These substances, including histamine, move into various parts of your body, such as your respiratory system, to cause allergy symptoms including runny nose, itchy eyes, and sneezing, among others.
Antihistamines are medications that block the action of histamines and relieve your allergy symptoms. ZYRTEC contains an antihistamine.
In some people, certain medicines, insect venom, or foods may also cause allergic reactions. See your doctor promptly if you suspect you are having an allergic reaction to these substances. These allergies are not the same as respiratory allergies like hay fever, and are not treated with the same medicines. See your doctor promptly if you suspect you are having an allergic reaction to these substances. The information in this Web site addresses only respiratory allergies.