Side Effects of an Allergy Shot: What to Expect From Your Next Injection
Before your next allergy shot, confirm your asthma is well-controlled, avoid intense exercise for 2 hours beforehand, and plan to stay for the full 30-minute observation. Normal reactions — a small red bump, mild itching — resolve within hours. Swelling beyond palm-size or any symptom outside the injection arm should prompt an immediate call to your care team. Large local reactions peak at 24-48 hours.
8 peer-reviewed sources
Normal side effects from a single allergy shot include mild redness and swelling at the injection site, resolving within hours. Stay for the 30-minute wait, avoid exercise afterward, and watch for any symptoms outside the injection arm.
Key facts
A 2026 observational cohort of 2,897 patients on at-home sublingual immunotherapy reported clinically meaningful improvement rising from 28% at 12 months to 45% at 24 months, showing how benefit accrues with time on treatment rather than arriving early.
Your Pre-Visit and Post-Visit Guide for One Allergy Shot Appointment
When you are thinking about one specific upcoming allergy shot — not the full treatment arc, just the next appointment — you want practical, actionable information: what to do beforehand, what is normal after, what is not normal, and exactly when to call someone.
The singular 'allergy shot' framing matters. Your concern is not the 3-5 year treatment journey today — it is the visit on Tuesday afternoon, and whether what happened at the last one (maybe some arm swelling, maybe a little dizziness) is something you should have told your allergist about, and what you should do differently this time.
This page is organized as a practical checklist rather than a clinical deep-dive. The key numbers you need: normal local reactions occur in 26-86% of patients and are expected (James & Bernstein 2017, Curr Opin Allergy Clin Immunol). Systemic reactions — those outside the injection arm — occur in 0.1-0.2% of injection visits (Bernstein 2010, Ann Allergy). A large safety study of self-administered allergen immunotherapy (Schaffer et al., 2015) found a comparable systemic reaction rate of just 0.16% per patient across 23,614 patients and 2,021,600 injections, with no fatalities — lower than the 3%–14% typically seen with office-based shots. The 30-minute observation window captures approximately 85% of systemic reactions (Epstein 2011, Ann Allergy).
Before any injection, your allergist benefits from knowing your complete allergen profile. At-home allergy testing options like Curex can confirm exactly which allergens are included in your treatment vial and ensure your sensitization profile is fully mapped before each treatment phase.
Check three things before every allergy shot: asthma is controlled, you have not exercised intensely in the past hour, and you know the difference between normal arm swelling and the warning signs that need immediate clinic attention.
Ready to skip the surprise bills?
At-home allergy shots (SCIT) are designed by board-certified allergists. See the listed SCIT plan rate in our pricing record and request a quote for eligibility, initiation and total care costs.
- MD-ledBoard-certified allergists
- QuoteTotal care estimate
- 50K+Patients treated
- HSA/FSAEligible
Same proven results. No clinic visits.
Curex at-home allergy shots are clinician-supervised; confirm your current program quote before enrolling.
Join the waitlistCurex allergy shot serum is compounded at a specialty pharmacy for each patient, and the FDA does not review compounded products for safety or efficacy.
At-Home SCIT vs SLIT: The Side Effect Difference
For patients who want effective immunotherapy without weekly clinic trips, understanding how the side effect profile of SCIT compares to sublingual immunotherapy (SLIT) helps frame the decision about which modality fits better with their life and risk tolerance. The shot itself is now available at home through Curex for eligible patients — with the first injection from each new vial or concentration supervised live in the Virtual Shot Room and a prescribed epinephrine auto-injector on hand.
| Treatment | Efficacy | Duration | Cost (5yr) | Convenience | Safety |
|---|---|---|---|---|---|
At-Home Allergy Shots (SCIT) — CurexBest | Disease-modifying; many patients achieve significant improvement | 3-5 years | $3,000-10,000 with insurance | At-home self-injection with Curex; needle; the first injection from each new vial or concentration supervised live in the Virtual Shot Room with a brief self-observation; avoid exercise 2 hrs after | Local reactions 26-86%; systemic 0.1-0.2% of doses; managed with gradual escalation, Virtual Shot Room–supervised first and changed doses, and a prescribed epinephrine auto-injector on hand |
Sublingual Drops (SLIT) | Comparable disease modification for grass, ragweed, and HDM allergens | 3-5 years, daily at home | Lower after eliminating clinic travel costs | Daily drops under the tongue at home; no needles; no commute; no observation period | No injection reactions; oral itching or throat irritation in 40-75%; no confirmed fatalities worldwide |
Antihistamines (OTC) | Symptom control only; no disease modification | Ongoing indefinitely | $500-2,000 | Daily pill; no clinic visits | No injection reactions; drowsiness or dry mouth possible |
- Efficacy
- Disease-modifying; many patients achieve significant improvement
- Duration
- 3-5 years
- Cost (5yr)
- $3,000-10,000 with insurance
- Convenience
- At-home self-injection with Curex; needle; the first injection from each new vial or concentration supervised live in the Virtual Shot Room with a brief self-observation; avoid exercise 2 hrs after
- Safety
- Local reactions 26-86%; systemic 0.1-0.2% of doses; managed with gradual escalation, Virtual Shot Room–supervised first and changed doses, and a prescribed epinephrine auto-injector on hand
- Efficacy
- Comparable disease modification for grass, ragweed, and HDM allergens
- Duration
- 3-5 years, daily at home
- Cost (5yr)
- Lower after eliminating clinic travel costs
- Convenience
- Daily drops under the tongue at home; no needles; no commute; no observation period
- Safety
- No injection reactions; oral itching or throat irritation in 40-75%; no confirmed fatalities worldwide
- Efficacy
- Symptom control only; no disease modification
- Duration
- Ongoing indefinitely
- Cost (5yr)
- $500-2,000
- Convenience
- Daily pill; no clinic visits
- Safety
- No injection reactions; drowsiness or dry mouth possible
If the weekly clinic visit is a barrier to consistent treatment, Curex delivers the allergy shot itself at home — a USP <797> sterile-compounded SCIT serum, with candidacy confirmed by a board-certified allergist, the first injection from each new vial or concentration supervised live in the Virtual Shot Room, and a prescribed epinephrine auto-injector on hand. program-specific pricing confirmed by quote, treating the same allergen triggers as in-clinic shots without the weekly commute.
Join the waitlistWhat to Expect Before, During, and After Your Allergy Shot
The following checklist-style guide walks through each phase of a single allergy shot appointment, covering what is expected, what to watch for, and what actions to take at each stage. Each section is kept brief and action-oriented — because when you are preparing for an appointment or monitoring after one, you need decisions, not narratives. All thresholds below are based on clinical practice standards from the 2011 AAAAI/ACAAI Practice Parameter Third Update (Cox et al., JACI 2011) and reaction timing data from the AAAAI/ACAAI National Surveillance Study (Bernstein 2010; Epstein 2011; Epstein 2019). The WAO reaction grading system (Cox 2010, JACI) provides the classification framework used here.
First: asthma control. Uncontrolled asthma is the single most important individual risk factor for severe allergy shot reactions — present in 88% of confirmed immunotherapy fatalities (Bernstein 2004, JACI). If your asthma has been flaring, you are using your rescue inhaler more than twice a week, or you have had nighttime awakenings, contact your allergist before the visit. Second: exercise. Intense physical activity in the hour before an injection can increase circulation and reaction risk. Standard guidance is to avoid vigorous exercise for at least 2 hours before your shot. Third: peak pollen season status. If you are in your relevant pollen season (for example, a grass-allergic patient in May), your allergist may proactively reduce your dose. Do not assume this will happen — mention it if your symptoms have been worse this week.
Confirm asthma is controlled. Avoid intense exercise for 2 hours before. Mention to your care team if you are in peak pollen season, if your asthma has worsened, or if you recently started or stopped any medications (especially beta-blockers).
Immediately after the injection, a small red wheal under 2.5 cm (the size of a US quarter) with mild itching is completely normal. This is mast-cell degranulation in direct response to the allergen extract. Stay seated, stay calm, and stay monitored. The 30-minute observation window exists because approximately 85% of systemic reactions begin within it (Epstein 2011, Ann Allergy) — which is why you keep your prescribed epinephrine auto-injector on hand and, with at-home SCIT, the first injection from each new vial or concentration is supervised live in the Virtual Shot Room. During the 30 minutes, if you notice any of the following, notify your care team immediately and do not wait to see if it resolves — using your epinephrine and calling 911 for any breathing or throat involvement: hives anywhere other than the injection arm, sudden sneezing or nasal congestion, throat tightness, chest tightness or wheezing, dizziness, or stomach cramping. A single isolated LLR at your last visit does NOT predict a systemic reaction this visit (Tankersley 2000, JACI) — so a previous large reaction does not mean you should expect a worse one today.
Stay put and monitored for the full 30 minutes — cutting the window short is never worth the risk. Apply ice to the injection site if it is uncomfortable. Report any symptom outside the injection arm to your care team during that window, and use your prescribed epinephrine and call 911 if it is systemic.
Approximately 15% of systemic reactions from allergy shots begin after the 30-minute window — meaning after you have already left the clinic (Epstein 2011; Epstein 2019). This does not mean you should spend the afternoon anxious. It means you should avoid driving alone immediately after each injection on your first several visits (or anytime your protocol changes), and you should know the warning signs to watch for. Avoid intense exercise for at least 2 hours after your shot — exercise can amplify systemic reactions by accelerating allergen absorption through increased circulation. A new vial being started at this appointment is an additional reason to be more vigilant over the next few hours, since batch potency can vary between vials and dose reductions are standard but not universal.
Call your allergist's office immediately if systemic symptoms develop at home. If symptoms are progressing rapidly — throat swelling, difficulty breathing, faintness — use your prescribed epinephrine auto-injector and call 911. Avoid intense exercise for 2 hours post-injection.
Large local reactions (LLRs) — defined as swelling exceeding 2.5 cm persisting beyond 24 hours — peak at 24-48 hours post-injection and may take several days to fully resolve (James & Bernstein 2017, Curr Opin Allergy Clin Immunol). LLR rates per injection range from 0.4% (LOCAL Study, Calabria 2009) to 5.3% (Roy 2007). If you wake up the morning after your shot with significant arm swelling, this is an LLR — uncomfortable, but not dangerous by itself. CALL YOUR ALLERGIST before your next injection if: the LLR is palm-sized or larger; this is your second or third consecutive LLR (a pattern of recurrent LLRs is associated with a 41.7% systemic reaction rate in the REPEAT Study, Calabria 2011); or you also experienced any systemic symptoms in the hours after your shot. Emergency: anaphylaxis signs (breathing difficulty, throat swelling, blood pressure drop) require epinephrine auto-injector use and 911 immediately. Fatal reactions occur at approximately 1 per 9 million injection visits (Epstein 2019) — extremely rare, and strongly linked to delayed epinephrine use.
For LLR: ice, antihistamine, call allergist before next appointment. For suspected anaphylaxis at home: use epinephrine auto-injector immediately, call 911, and monitor for biphasic recurrence up to 72 hours later.
When to Worry: Decision Guide
Is the reaction limited entirely to the injection site arm (redness, swelling, itching only at the needle location)?
Local reaction — expected and manageable
Ice for 10-20 min, antihistamine if needed. Report to allergist before next visit if swelling exceeds palm size or this is a recurring pattern.
Possible systemic reaction
Notify your care team immediately, and use your prescribed epinephrine auto-injector and call 911 if the symptom is systemic. Any symptom outside the injection arm — hives elsewhere, throat tightness, wheezing, dizziness — needs prompt evaluation.
Did your last shot cause a larger-than-usual local reaction?
LLR — report before next injection
Call your allergist's office before your next appointment to describe the reaction size and duration. They may recommend a dose adjustment, premedication, or a slower escalation schedule.
Standard local reaction history
Continue with the scheduled protocol. Report any new pattern of increasing local reactions to your allergist.
Frequently asked questions
What should I do before my allergy shot appointment?
Three pre-visit checks matter for every allergy shot appointment. First, confirm your asthma is well-controlled — uncontrolled asthma is present in 88% of confirmed immunotherapy fatalities (Bernstein 2004, JACI), and injections should be delayed if your asthma is actively flaring. Second, avoid intense exercise for at least 2 hours before your shot, since vigorous activity increases circulation and can amplify the systemic distribution of the injected allergen. Third, inform your allergist if you are in your peak pollen season, if you recently started or stopped any medications (especially beta-blockers or ACE inhibitors), or if you had a significant local or systemic reaction at your last visit. These three pieces of information help your allergist make the dose decision for the day.
What is a normal allergy shot reaction at the injection site?
A normal reaction at the injection site is a small red wheal — smaller than a US quarter, roughly 2.5 cm or less — with mild itching and warmth that develops within minutes of the shot and resolves within a few hours. Apply ice for 10-20 minutes and take an oral antihistamine if the itching is bothersome. Mild arm soreness is also normal, similar to a flu vaccine. If the swelling is still present the next morning and has grown larger than expected, this is a large local reaction (LLR) — peaks at 24-48 hours and resolves over several days. An LLR looks more alarming than it is. It warrants a call to your allergist before your next injection, but it is not a medical emergency on its own (James & Bernstein 2017, Curr Opin Allergy Clin Immunol).
Can I exercise after an allergy shot?
You should avoid intense exercise for at least 2 hours after each allergy shot. Physical activity increases your heart rate and circulation, which can accelerate the systemic absorption of the allergen extract and potentially increase the risk of a systemic reaction. Light walking or gentle activity is generally acceptable, but vigorous exercise, hot showers, saunas, and hot tubs should all be avoided during the 2-hour post-injection window. Some allergists extend this recommendation to 4 hours for patients who are starting a new vial, entering peak pollen season, or have a history of previous systemic reactions. If you exercised immediately before your last injection and had a reaction, mention this to your allergist — the timing may be relevant.
What happens if I leave the clinic before the 30 minutes is up?
Leaving before the 30-minute observation window is complete significantly increases the risk that a systemic reaction will occur without trained medical staff present. Approximately 85% of systemic reactions from allergy shots begin within 30 minutes (Epstein 2011, Ann Allergy), which means the observation period is specifically designed to catch the great majority of reactions while epinephrine and resuscitation equipment are immediately available. If you leave early and a reaction develops, you may be alone, without epinephrine, and too far from emergency care for timely treatment. Three of 17 confirmed fatalities in the Bernstein 2004 survey occurred after patients had already left the clinic — underscoring how the 30-minute window is a safety infrastructure element, not a bureaucratic formality.
What should I do if I had a bigger reaction at my last appointment?
Contact your allergist's office before your next injection to describe what happened in detail — the size of any local swelling, whether symptoms appeared outside the injection arm, and how long they lasted. Your allergist will use this information to adjust your protocol. After a Grade 1 systemic reaction (mild hives or sneezing only), the standard approach is to reduce to approximately 50% of the reaction-causing dose. After a Grade 2 reaction (multiple organ systems), a more significant reduction of about 10% of the reaction-causing dose is typical. Your allergist may also recommend antihistamine premedication for future visits, a slower escalation schedule, or extended observation time. A single large local reaction at the injection site without any systemic symptoms typically does not require dose adjustment, though recurrent large local reactions do warrant discussion (Calabria 2011, REPEAT Study, Ann Allergy).
Is it safe to get an allergy shot when I have a cold or feel sick?
Getting an allergy shot when you are acutely ill, especially with a respiratory infection, is generally not recommended and may be postponed by your allergist. Active illness — particularly respiratory infections — can cause temporary changes in airway reactivity that are similar to uncontrolled asthma, potentially increasing your reaction risk during the injection. The 2011 AAAAI/ACAAI Practice Parameter recommends pre-injection assessment of symptoms, and most allergists will delay an injection if you have fever, active wheezing, or significant upper respiratory symptoms. Call your allergist's office before your appointment if you feel unwell — most practices would rather reschedule than risk an injection on a day when your baseline is altered. Missing one or two injections due to illness is manageable; your allergist will adjust the dose when you return depending on how long the gap was.
Should I tell my allergist if my last shot caused significant swelling?
Yes — always report significant injection-site swelling to your allergist before your next injection. A large local reaction (swelling larger than a quarter that persists beyond 24 hours) does not automatically require a dose change, but it does give your allergist important information for protocol management. The AAAAI/ACAAI Practice Parameter notes that while an individual LLR does not predict the next injection's reaction (Tankersley 2000, JACI), a pattern of recurring LLRs has been associated with a 41.7% systemic reaction rate in the REPEAT Study (Calabria 2011, Ann Allergy). Your allergist may recommend dose adjustment, antihistamine premedication, or a slower escalation pace if LLRs are recurring. Reporting is always the right call — your allergist can only optimize your protocol with accurate information about your reaction history.
Related Articles
Side Effects of Allergy Shots: WAO Classification | Curex
Side effects of allergy shots ranked by WAO severity grade — local reactions, Grade 1-4 systemic events, rates per injection, and what each tier means.
Read moreAllergy Shot Side Effects: Fatigue Evidence Review | Curex
Fatigue after allergy shots is real but unquantified in trials. Learn the biological mechanism, expected timeline, and red-flag signs to watch for.
Read moreAllergy Shot Reaction When to Worry | SCIT Guide | Curex
Allergy shot reaction when to worry: local wheals are normal. Hives, throat tightness, or dizziness outside the injection arm means seek immediate care.
Read moreWhat Is Allergy Shots? Quick Definition and How It Works
What is allergy shots? SCIT retrains the immune system over 3–5 years and is the only disease-modifying allergy treatment; many patients get long-term relief that can persist after treatment.
Read moreAllergy Steroid Shot Side Effects — Kenalog vs SCIT | Curex
Kenalog steroid shots are NOT allergy immunotherapy. Learn the key differences, real side effects, and why AAAAI guidelines advise against depot steroids.
Read moreAllergy Shot Side Effects: Per-Injection Timeline | Curex
What happens after each allergy shot? A minute-by-minute timeline from the 30-min wait to 48-hour local reactions, with safety thresholds and real data.
Read moreGet your allergy shots — without the clinic.
Curex at-home shots require a program quote. Confirm what is included in your plan — a personalized serum compounded to USP <797> sterile standards, board-certified allergist oversight, and one weekly injection you give yourself at home. No clinic visits, no facility fees. HSA/FSA eligible.
Program quote required · Remaining payments for shipped treatment are collected on cancellation
Curex allergy shot serum is compounded at a specialty pharmacy for each patient, and the FDA does not review compounded products for safety or efficacy.
This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about a medical condition. Content reviewed by board-certified allergists at Curex.
Questions about Curex itself?
Straight answers about the company, the evidence, what patients report, and what it costs — including the parts that are not flattering.