One of the most widespread illnesses around, allergies are an overreaction of the immune system to substances – known as allergens – that are otherwise harmless. Allergens are substances that are foreign to the body and can cause an allergic reaction. Strictly speaking, allergy is one of four forms of hypersensitivity, which can result in an extreme inflammatory response. Common reactions include eczema, hives, hay fever, asthma attacks, food allergies, and reactions to the venom of stinging insects such as wasps and bees.
Mild allergies, like hay fever, are highly prevalent in the human population and cause symptoms such as allergic conjunctivitis, itchiness, and runny nose. 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 anaphylactic reactions.
A variety of tests now exist to diagnose allergic conditions. Treatments for allergies include allergen avoidance, use of antihistamines, steroids or other oral medications, targeted therapy, and immunotherapy to desensitize the response to allergen.