Allergies

An allergy is an exaggerated reaction of the immune system to a substance that is normally harmless. These substances, called allergens, include pollen, dust mites, animal dander, certain foods, insect stings, medications, and natural rubber latex. When an allergic person comes into contact with an allergen, the immune system produces antibodies called IgE.

These trigger the release of chemicals such as histamine, leading to symptoms that may affect the nose, eyes, skin, lungs, or digestive system. Depending on the person and the allergen, reactions can include sneezing, itchy eyes, hives, eczema, coughing, wheezing, abdominal pain, vomiting, or diarrhea. Symptoms may appear within minutes or several hours after exposure, depending on the type of allergy involved.

Some allergic reactions are mild and disappear quickly, while others require medical treatment. In rare cases, a severe reaction called anaphylaxis can develop. It may cause swelling of the throat, difficulty breathing, a sudden drop in blood pressure, and loss of consciousness. This is a medical emergency that requires immediate treatment with epinephrine.

Allergies are diagnosed using a person's medical history, physical examination, and, when appropriate, skin or blood tests. Although allergies cannot always be prevented, avoiding known allergens, following the prescribed treatment, and carrying emergency medication when needed help most people live active and healthy lives.