Immunotherapy describes a treatment aimed at increasing the tolerance of an individual's immune system for a substance to which they are allergic. It is a process that involves exposing an individual to small amounts of the allergen in a safe way over time. It cannot be used for all allergies but has been used to treat allergies to house dust mites, pollen, cat or dog fur and wasp and bee stings.

The treatment involves the injection of small amounts of the allergen under the skin. The procedure is relatively safe but it has to be performed in a hospital setting because there is a small risk of a severe allergic reaction known as anaphylaxis. The procedure needs to be repeated at regular intervals to induce a change in the immune response. The treatment may not completely treat an allergy but will typically reduce the severity of the reaction allowing them to cope better with their symptoms.