Allergy shots, also known as subcutaneous immunotherapy (SCIT), are a long-term treatment designed to address the root cause of allergic symptoms. This therapy involves injecting gradually increasing doses of specific allergens, such as pollen or dust mites, into the body. The goal is to slowly desensitize the immune system, shifting its response from an allergic reaction to a state of tolerance. SCIT can lead to a significant reduction in allergy symptoms and a decreased need for daily allergy medications.
Standard Injection Method for Allergy Shots
Allergy shots are administered via a subcutaneous injection, delivering the allergen extract into the fatty layer of tissue just beneath the skin. This method is distinct from an intramuscular (IM) injection, which penetrates deeper into the muscle tissue, like a standard vaccine. The needles used for SCIT are typically much shorter and finer than those used for IM injections.
The standard site for this procedure is the upper arm, specifically the mid-posterolateral area, where there is sufficient subcutaneous tissue. This placement is deliberate for safety and effectiveness. Intramuscular administration is avoided because faster absorption into the bloodstream significantly increases the patient’s risk of a severe systemic allergic reaction, or anaphylaxis.
Optimizing Safety Through Subcutaneous Delivery
The selection of the subcutaneous layer is a strategy for managing risk. Subcutaneous tissue has a less dense network of blood vessels compared to highly vascularized muscle tissue. This difference allows the allergen extract to form a temporary reservoir, ensuring a slower, more controlled absorption rate over time.
This slow absorption minimizes the risk of a severe systemic reaction that occurs with rapid uptake. Faster uptake from a muscle injection would flood the system with allergen, potentially overwhelming the immune system. The controlled release allows the body to process the allergen gradually, preventing an immediate shock to the system.
Immunologically, the subcutaneous space contains specialized immune cells, such as dendritic cells. As the allergen slowly diffuses, these cells capture the antigen and process it in a way that promotes tolerance rather than allergy. Successful SCIT encourages the production of protective antibodies, particularly Immunoglobulin G4 (IgG4), which block the allergic antibody IgE from binding to the allergen. The gradual exposure also helps shift the immune response away from allergic T helper 2 (Th2) cells toward a more balanced profile.
The Allergy Shot Treatment Schedule and Patient Monitoring
Subcutaneous immunotherapy is divided into two distinct phases that manage the dose and frequency of allergen exposure. The first is the build-up phase, where patients receive injections frequently, typically one to three times per week, for three to six months. During this time, the concentration of the allergen in each shot is gradually increased to build the patient’s tolerance.
Once the highest tolerated dose is reached, the patient transitions into the maintenance phase, which aims to sustain tolerance. The dose remains fixed, but the frequency of injections is significantly reduced, usually to once every two to four weeks. This maintenance period lasts an average of three to five years to ensure lasting clinical benefits.
A safety protocol requires patients to remain in the clinic for 20 to 30 minutes after receiving their dose. This observation period ensures that medical staff can immediately recognize and treat any adverse systemic reactions, which most commonly occur within this window. Dosing is continuously adjusted by the allergist based on the patient’s overall tolerance and localized reactions, such as swelling or redness at the injection site.