How Allergy Shots Work: The Step-by-Step Process Explained

Your first at-home allergy shot starts with reviewing your allergy test results with your allergist over video, discussing the custom extract that's been compounded for you, and giving your very first injection — an extremely small dose — under live Zoom supervision by the prescribing allergist. After the injection, you stay put for a 30-minute observation period with your prescribed epinephrine auto-injector on hand. Your allergist checks the injection site for any local reaction (some redness or swelling is normal and expected). If you have no adverse reaction, you're cleared and given instructions for your next dose — typically 3-7 days later, with a slightly increased amount. The first injection is deliberately tiny, so most people feel nothing beyond mild arm soreness. Report any unusual symptoms — hives, throat tightness, wheezing — to your care team immediately during the observation period.

For each allergy shot appointment, bring your photo ID and insurance card (or payment information for self-pay visits), your rescue medications — especially epinephrine auto-injector if prescribed, and any antihistamines used for shot-related reactions. Many patients bring something to do during the 30-minute observation wait: a book, phone, or laptop. Wear clothing that makes your upper arm easily accessible — a short-sleeve shirt or a shirt with sleeves that push up easily. Avoid intense exercise for 2 hours before and after your appointment, as elevated heart rate can increase reaction risk. Tell the nurse or allergist about any illness, asthma flare, or change in medications since your last visit — certain conditions (fever, active infection, unstable asthma) may require postponing the injection.

Your allergist determines your target maintenance dose based on established clinical guidelines and your specific allergen testing results. The AAAAI/ACAAI Practice Parameter specifies a target range of 5-20 micrograms of the major allergen protein per injection for most inhalant allergens. For standardized extracts (grass, dust mites, cat), this corresponds to specific dose ranges in standardized units (BAU or AU). For unstandardized extracts (dog, many molds, cockroach), dosing is based on protein nitrogen units (PNU) or weight-to-volume concentrations. Your custom extract vial is prepared by a compounding laboratory or your allergist's office, calibrated to your specific test results and the target therapeutic dose. Each injection increases incrementally toward this target — if you have large local reactions, the increase may be slowed or the dose held until reactions resolve.

Most allergists recommend postponing your allergy shot if you have an active infection with fever, uncontrolled asthma, or a significant illness — these conditions increase the risk of adverse reactions to the injection. A mild cold without fever is usually manageable, but you should call your allergist's office before your appointment so they can advise based on your specific situation and the dose you're currently receiving. Certain other circumstances also warrant discussion before each shot: worsening asthma symptoms, starting or stopping certain medications (particularly beta-blockers, which complicate epinephrine treatment), significant increase in allergic symptoms suggesting very high allergen exposure, pregnancy onset, or any significant change in your health since your last visit. When in doubt, call the clinic — the nurse can advise over the phone whether to come in or postpone.

When you and your allergist agree that your allergy shot course is complete — typically after 3-5 years of maintenance with good symptom control — you simply stop receiving injections. There is no tapering process; you end at your maintenance dose and do not need to continue. Most patients then enter the post-treatment benefit phase, during which the immune tolerance established during treatment continues to protect against allergic symptoms for years. Durham et al. (NEJM, 1999) confirmed no difference in symptom or medication scores between patients who stopped after 3-4 years and those who continued maintenance for up to 3 additional years. You may notice some return of mild symptoms seasonally, especially in high-exposure years, but typically far less severe than before treatment. Some patients relapse and need a second course; a second course typically works faster than the first since some immune memory persists.