Allergy shots, formally called immunotherapy, are regular (e.g., weekly or monthly) injections under the skin. Allergy shots introduce a very small amount of an irritating substance (an allergen, such as tree pollen) to the body of a person with allergies, so that the immune system is conditioned to stop reacting to normal levels of that allergen. Immunotherapy is typically given for 3 to 5 years, although some people need longer treatment to remain less sensitive to allergens. Allergy shots are effective at reducing allergy and even asthma symptoms, and they are associated with few side effects.
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Local Side Effects
The most common side effects of allergy shots occur at the injection site, because the allergy shots contain a small amount of the allergens specific to a patient. Redness, swelling and itch can begin immediately or within a few minutes of the allergy shot. In some instances, local reactions can occur four to eight hours after the shot. These reactions to shots may be recorded and compared with reactions from allergy skin testing (i.e., prick tests) that are used to identify allergens. In addition, bruising is possible at the injection site.
Bruises may occur only occasionally, or even at each shot in sensitive people; they usually cover a small area and are temporary. Bruising is most common when shots are given into a muscle. Most local reactions typically occur within the first 20 minutes after an injection.
In some cases, allergy shots can worsen allergic reaction symptoms and cause cough, wheeze and other bodily reactions to the allergen. Continued wheezing and chest tightness are also possible. Allergy symptoms are more likely to occur when a regular schedule of allergy shots is not observed; a basis of successful allergy shot treatment is the continued administration of immunotherapy to provide constant levels of the allergen to the body. In some cases, allergy symptoms can develop after extended local reactions; reporting local reactions to the doctor to adjust allergy shot contents can help decrease local and allergic reactions with future shots.
Rarely, the life-threatening symptoms of anaphylaxis can occur from zero to 30 minutes after an allergy shot. Symptoms include low blood pressure, chest tightness and wheezing that alters or blocks breathing and may cause unconsciousness. Anaphylaxis is a medical emergency often treated with epinephrine injections to reverse the body's over-reaction. In most cases, people who get allergy shots remain at the doctor's office or nurse's station for up to 30 minutes to identify side effects, including anaphylaxis.