What Are in Allergy Shots? How Your Allergist Builds Your Custom Mix

Allergy shots are personalized to each patient's specific sensitization profile — even two people with apparently similar allergies may have different IgE reactivity levels, different clinically relevant allergens, and different regional allergen exposures. Your friend may be more sensitized to dust mites while you have stronger reactions to grass pollen, or your allergist may have made different clinical judgments about which allergens to include based on symptom history. Additionally, extract concentrations in the maintenance vial may differ — your allergist calibrates the target dose based on your reactivity level and tolerance. No two patients receive identical formulations because no two patients have identical immune profiles.

Yes, your allergist can add new allergens between vial refills — typically when you complete a vial and a new one needs to be prepared. This might happen if you develop a new sensitization, if you move to a new geographic area with different regional allergens, or if your symptoms suggest an allergen not covered in your original formulation. When new allergens are added, the vial concentration must be adjusted to maintain appropriate per-allergen doses, and you may need to restart the escalation schedule for the new extract. Adding allergens mid-treatment is a routine clinical decision, though it requires a new vial to be formulated and may temporarily increase visit frequency.

Patients with multiple allergen sensitivities often need two or more vials because certain allergen combinations are chemically incompatible and cannot be stored together. Mold extracts (Alternaria, Cladosporium, Aspergillus) and cockroach extract contain proteases — enzymes that break down the protein structures of pollen and dust mite extracts when stored in the same vial. To preserve the potency of each allergen, your allergist separates incompatible extracts into different vials. One common arrangement is one vial for pollens and dust mites and a separate vial for molds and other problematic allergens. Each vial gets its own injection into the opposite arm to help track any local reactions.

If your allergy shot vial expires before you finish it — either because you missed too many appointments or the 12-month shelf life passed — a new vial must be prepared before treatment can resume. The expired vial cannot be safely used because extract potency declines over time, making dosing unreliable. When a new vial is prepared after a treatment gap, your allergist will typically set you back to a lower starting dose rather than resuming where you left off, particularly if the gap was long enough to cause immune tolerance to fade. This dose reduction reduces the risk of a systemic reaction upon resumption. Consistent appointment attendance is important for both therapeutic and practical reasons.

Your maintenance vial concentration is determined by the target maintenance dose for each allergen included. AAAAI practice parameters specify target maintenance doses for FDA-standardized allergens — for example, cat Fel d 1 target is 11-17 micrograms per injection, and dust mite Der p 1 target is 7-25 micrograms per injection for maintenance. For non-standardized extracts, the target is typically expressed as the highest tolerated dose established during build-up. Your allergist works backward from the maintenance target dose to calculate the extract concentrations needed in each vial, factoring in the 0.5mL injection volume that will be used for the maintenance phase. Patients with strong local reactions during build-up may have their maintenance concentration adjusted downward.

The allergen extract concentrates that your allergist orders from manufacturers are FDA-regulated biological products — manufactured under current Good Manufacturing Practice (cGMP) conditions by licensed facilities and subject to lot-release testing for potency, sterility, and identity. However, the final mixing and compounding of your personalized vial is a custom-compounding step — each patient's formulation is prepared to order rather than manufactured centrally. AAAAI/ACAAI compounding guidelines govern this process as professional standards. With Curex at-home SCIT, your personalized vial is sterile-compounded to USP <797> standards — the pharmacy-grade framework for sterile injectables — with lot-level sterility, potency, and endotoxin testing before shipping. This is the same regulatory principle as traditional allergist-office compounding, applied under a formal USP framework. Your Curex allergist follows strict protocols for formulation, labeling, cold-chain shipping, and expiration tracking.

Allergy shots start at extremely low doses — typically 1:1000 to 1:10000 of the maintenance concentration — because your immune system needs to be introduced to the allergen proteins gradually to avoid triggering a systemic allergic reaction. At these initial concentrations, the allergen dose is below the threshold for mast cell activation but sufficient to begin the tolerance-signaling process. As your immune system adapts with each injection, the dose increases incrementally — both by increasing the volume within each vial and then by advancing to higher concentration vials. The build-up phase typically involves 50-80 individual injections over 8-28 weeks before reaching the target maintenance dose. The slow escalation is not arbitrary — it is precisely calibrated to the limits of immune tolerance induction.