Allergies occur when the immune system reacts to a foreign substance, known as an allergen, that is usually harmless to most people. When a person with allergies comes into contact with an allergen, their immune system produces antibodies that identify the allergen as harmful, even though it is not. The immune systems reaction can inflame the skin, sinuses, airways, or digestive system, depending on the type of allergy.

Allergens can be found in various substances, including pollen, animal dander, dust mites, mold, certain foods, insect stings, medications, and latex. The severity of allergies varies from person to person and can range from minor irritation to anaphylaxis, a potentially life-threatening emergency.

Symptoms of allergies depend on the type of allergy and can range from mild to severe. Common symptoms include congestion, watery eyes, a runny nose, vomiting, hives, and in severe cases, anaphylaxis.

To diagnose allergies, doctors review the patients personal and medical history, give a physical exam, and do tests to identify the allergens. Treatment for allergies depends on the severity of the symptoms and can include avoidance of allergens, medication options, and immunotherapy.

Common allergens include pollen, dust mites, pet dander, insect stings, certain foods, and latex. Allergy is one of the major factors associated with the cause and persistence of asthma.