Allergy shots (immunotherapy) are a treatment in which an offending allergen is injected under a patient’s skin in tiny doses. Common allergens include pollens, pet dander, dust, or the venom contained in certain insect stings (such as bees, wasps, hornets, fire ants). In some cases, a physician will use allergy shots to desensitize an individual to certain drug allergies. This may be done when the drug is vital to the patient's health and when there are no alternatives. However, most physicians prefer instead to look for alternative drugs to replace the drug to which the individual is allergic.

The goal of allergy shots is to increase the body’s tolerance of a specific allergen. In many cases, the patient’s tolerance level to these allergens rises dramatically, causing a significant reduction in symptoms such as runny nose, itchy eyes and scratchy throat. This accomplishes one or more of the following:

• Prevents the onset of symptoms
• Lessens the frequency of reactions
• Lessens the severity of symptoms resulting from a reaction

Those who undergo allergy shot treatment report high success rates, especially in the treatment of allergic rhinitis. According to a study published in the Annals of Allergy, Asthma & Immunology:

• 81 percent of patients felt the therapy had been a success
• 19 percent were unsure of the shots’ effectiveness
• Emergency room visits declined by 68 percent
• Days lost from school dropped by 75 percent

It is not clear how allergy shots build this tolerance. In some cases, researchers have found that the injections stimulate the production of blocking immunoglobulin G (IgG) antibodies, which bind to the allergen. This is important, because it prevents another antibody – immunoglobulin E (IgE) – from binding to the allergen. IgE is the antibody that triggers mast cells to start the allergic reaction. The shots may also decrease the body's production of IgE.

Potential immunotherapy candidates undergo extensive allergy skin tests, blood tests and physical examination to help pinpoint the offending allergen. During the first injection, the patient will receive a saline solution (dilute salt water) mixed with a very low dose of the troublesome allergen. The patient typically is monitored for 30 minutes to make sure the injection has not triggered a reaction such as shortness of breath, runny nose or tight throat. In addition, patients will be monitored for signs of anaphylaxis, a rare, life-threatening allergic reaction that demands immediate medical attention.

Patients who do not have a reaction to the trace amount of allergen usually will be discharged until the next treatment session. If patients have a reaction after leaving the medical facility, they should immediately return to the facility or visit an emergency room.

After the initial injection, a patient will return for periodic follow-up treatments. These injections typically take place once or twice a week over the course of several years. With each successive treatment, the amount of allergen injected under the skin is increased.

When effective, immunotherapy can dramatically reduce a patient’s sensitivity to certain allergens, with the first benefits becoming apparent in as little as six months.

Once the first phase of treatment is finished, injections are given with less frequency, typically monthly for a period of three to seven years. At some point, the patient’s tolerance may grow to the point where further shots are unnecessary. Generally, discontinuation of the treatments is recommended after a patient has demonstrated minimal symptoms over two consecutive seasons of exposure. Those who begin to experience symptoms again later can undergo another round of immunotherapy.

Though allergy shots are currently available only as an injectable treatment, a similar method of immunotherapy that involves medicine placed under the tongue has proven effective in early testing. Though more research is required before the treatment is accepted by the wider scientific community, this type of immunotherapy may one day be available as an alternative to allergy shots.