Subcutaneous Immunotherapy (SCIT), commonly known as the allergy shot, is a long-term treatment designed to offer relief from allergy symptoms. Unlike standard allergy medications that only mask symptoms, SCIT works similarly to a vaccine, training the immune system to tolerate substances that once triggered a reaction. The therapy involves administering small, controlled doses of a specific allergen extract via injection, typically into the upper arm, to achieve long-lasting desensitization that can significantly reduce or eliminate allergic symptoms for years, even after treatment is stopped.
Determining Candidacy for Immunotherapy
A comprehensive medical evaluation by an allergist is the only way to determine if a person is a suitable candidate for allergy shots. The process begins with identifying the specific triggers through skin or blood allergy tests, ensuring the treatment is precisely tailored to the individual’s confirmed allergies. SCIT is generally effective for allergies caused by airborne substances like pollen, pet dander, dust mites, and molds. It is also an effective treatment for severe reactions to stinging insect venom.
SCIT is not used to treat food allergies, medication allergies, or chronic hives. Certain pre-existing health conditions can also make the treatment unsafe or less effective, such as uncontrolled or severe asthma, due to the risk of worsening symptoms.
Patients taking beta-blocker medications are typically excluded because these drugs can interfere with the emergency treatment for a severe allergic reaction. While both children and adults can receive the shots, treatment is usually not recommended for children under the age of five. SCIT is also not initiated during pregnancy, though a clinician may consider continuing maintenance doses if a patient becomes pregnant during treatment.
The Standard Treatment Protocol
Allergy shot therapy is divided into two distinct periods, requiring a significant commitment of time and consistency from the patient. The first phase is the build-up phase, where the goal is to gradually introduce increasing amounts of the allergen extract. This initial period typically involves receiving injections once or twice a week for approximately three to six months. The dosage is progressively increased until the patient reaches the highest dose they can safely tolerate, known as the maintenance dose.
Once the patient reaches the maintenance dose, the frequency of injections decreases, often shifting to a schedule of once every two to four weeks. The entire maintenance phase usually lasts for three to five years.
The purpose of this extended period is to solidify the immune system’s new tolerance to the allergen, providing long-term relief. Adherence to the schedule is important, as missing doses, especially during the build-up phase, may require the dose to be lowered to prevent a systemic reaction.
How Allergy Shots Change the Immune System
Allergy shots work by desensitizing the immune system, modifying the way the body reacts to the offending allergen. The injections shift the immune response away from the production of Immunoglobulin E (IgE) antibodies, which drive allergic symptoms like sneezing, itching, and swelling. IgE antibodies attach to mast cells, causing them to release chemicals like histamine upon allergen exposure.
The repeated, controlled exposure encourages the immune system to generate Immunoglobulin G (IgG) antibodies. These IgG antibodies, often called “blocking antibodies,” intercept the allergen before it can bind to the IgE on the mast cells. This prevents the release of histamine and other inflammatory mediators, leading to a reduction in allergic symptoms and promoting a long-term state of immune tolerance.
Immediate Risks and Monitoring Requirements
While allergy shots are generally safe when administered correctly, they carry a small risk of inducing an allergic reaction. The most common side effects are local reactions, manifesting as redness, swelling, or itching at the injection site. These reactions are usually mild, typically resemble a mosquito bite, and often resolve within a few hours.
A less common but more serious concern is a systemic reaction, which involves symptoms beyond the injection site. These reactions can range from generalized hives, nasal congestion, and wheezing to more severe symptoms like throat swelling, chest tightness, or a sudden drop in blood pressure. The most severe systemic reaction is anaphylaxis, a life-threatening event that requires immediate emergency treatment.
Because most serious reactions occur shortly after the injection, a mandatory observation period is required at the clinic. Patients must remain under medical supervision for at least 20 to 30 minutes following the injection to ensure immediate access to staff and equipment capable of managing an adverse event. This post-injection monitoring is a non-negotiable safety measure, designed to protect the patient from the rare but serious possibility of a severe systemic reaction.