An allergy is a hypersensitivity disorder of the immune system. Symptoms include red eyes, itchiness, and runny nose, eczema, hives, or an asthma attack. Allergies can play a major role in conditions such as asthma. In some people, severe allergies to environmental or dietary allergens or to medication may result in life-threatening reactions called anaphylaxis. Food allergies and reactions to the venom of stinging insects such as wasps and bees are more often associated with these severe reactions. Not all reactions or intolerances are forms of allergy.