Allergy: a word used to describe an abnormal immune system response to a substance (allergen) that would otherwise be harmless.

Anaphylaxis: a life threatening allergic reaction. Symptoms may include hives, wheezing, nausea, vomiting, diarrhea, and swelling. If the swelling occurs in the airway, a person can die from lack of oxygen. In severe cases the allergic reaction may also cause low blood pressure which may cause a person to feel light-headed, pass out or possibly be fatal.

Asthma: a lung condition characterized by inflammation and spasm of the airways. This causes intermittent problems breathing such as coughing, wheezing and shortness of breath. Asthma can be triggered by infections, allergies, exercise, temperature changes or other airway irritants.

Atopic Dermatitis or Eczema: a skin condition more common in people with allergies. It often starts in early childhood. Symptoms include itching, dry skin, and a red rash that may get worse with infections, temperature changes, detergents or allergen exposure.

Epinephrine: an emergency medication that can reverse an allergic reaction. Studies have shown that in severe allergic reactions, prompt administration of epinephrine increases the likelihood that a person will recover from the reaction.

Food Intolerance: a condition whereby a person is unable to tolerate certain parts of foods. This is different from a food allergy because the immune system is not involved. An example is lactose intolerance, in which certain individuals cannot digest the sugar found in milk. Food intolerance is much more common than food allergy.

Histamine: a chemical released by cells of the immune system during an allergic reaction. Histamine causes many of the symptoms of allergy, such as itching, redness and swelling. Medications called antihistamines block the action of this chemical and prevent or reverse the signs and symptoms of an allergic reaction.

Hives or Urticaria: a rash that often is seen during allergic reactions. Hives are reddened, raised and itchy. They can vary in size (pencil eraser sized to covering larger areas of skin) and frequently come and go over minutes to hours.