It is actually not known exactly how allergy shots (or 'allergen immunotherapy' as it is sometimes called) works, but it seems to involve modifying the function of immune cells called T-regulatory cells so they give a more normal response to the allergen. Allergy shots is an approach which might help you control your allergy symptoms, but here are a couple of things to consider before you sign up for the treatment.
The following are suitable for treatment with allergy shots:
Note that the diagnosis of allergy must be confirmed by an allergy test/skin prick/blood tests before allergy shots are considered. They are not normally given to those over 50 or under the age of five years old. There are also a number of health conditions, such as heart disease, which will preclude the administration of allergy shots. In the UK, allergy shots are not generally used in the treatment of asthma.
There are a number of different regimes, depending on where you are treated. Typically an injection containing the allergy extract is given under the skin of the upper arm in gradually increasing doses till a maximum 'maintenance' dose is reached. This is then given at longer intervals for three to five years in total.
There is also oral immunotherapy, where the treatment is given by mouth. This is currently only available in the UK for grass pollen allergy (Grazax). The first dose is given under medical supervision, and then the treatment can be taken at home.
If it works, allergy shots can give relief to a severe allergy, saving the trouble and expense of treatment with drugs like antihistamines. Allergy drugs in general only treat the symptoms, but the effects of allergy shots can be long-lasting. Grass and birch allergen treatment can last for several years, but less is known about the long-term success of allergy shots for other allergens.
Some people don't like injections. Treatment through allergy shots lasts for up to three years so it requires a level of commitment on the patient's part. It must also be given under medical supervision (you can buy most other medical allergy treatments over the counter). More concerning is the fact that allergy shots can lead to serious, even life-threatening, allergic reactions, particularly if the dose is not carefully calculated (hence the need for expert supervision).
Allergens are proteins and the characterisation and purification of proteins is a hot topic in medical science. Therefore, it is likely that allergy shots for a wider range of allergens will be developed and, indeed, many biotech companies are doing just this. So we can expect further treatments to become available in the future. There will also be easier ways of delivering the treatments as an alternative to the injection – for instance, nasal drops, or tablets.