What are the side effects of allergy shots?
Short answer
Medication question
The most common side effect of allergy shots is a local reaction — redness, swelling, warmth, and itching at the injection site — that usually clears within a day. Less commonly, shots trigger whole-body symptoms like sneezing, hives, or throat tightness, and rarely a severe reaction called anaphylaxis, which is why you are observed for 30 minutes after each dose.
This is a general research summary, not medical advice. A pharmacist can confirm it for your situation.
Key facts
The most common side effect of allergy shots is a local skin reaction — redness, swelling, and itching at the injection site — which usually settles within a day.
Because of a small risk of a severe reaction shortly after an injection, allergy shots are given in an allergist's office where reactions can be treated immediately.
Anaphylaxis from allergy shots is rare, and poorly controlled asthma is one of the greatest risk factors for a severe systemic reaction.
A 2026 real-world study of 2,897 patients on telemedicine-delivered sublingual immunotherapy for environmental allergies reported clinically meaningful improvement rising from 28% at 12 months to 45% at 24 months, adherence above 90%, and no cases of anaphylaxis. It is observational, so it describes outcomes rather than proving superiority over in-person care.
Here's the nuance
A one-liner rarely tells the whole story. This is the honest detail behind the short answer above.
The most common side effect of allergy shots (subcutaneous immunotherapy) is a local reaction at the injection site — redness, warmth, swelling, and itching that typically appears within a few hours and settles within a day. These local reactions are expected and are usually managed with a cool compress, an oral antihistamine, or a topical steroid. Large local reactions are common, reported in roughly a quarter to more than three-quarters of injection courses in the medical literature.
Less often, allergy shots can cause a systemic reaction that affects the whole body — sneezing, nasal congestion, hives, itchy or watery eyes, coughing, or throat tightness. The most serious systemic reaction is anaphylaxis: a rare but life-threatening whole-body response that can include difficulty breathing, widespread swelling, a drop in blood pressure, and dizziness. Anaphylaxis is a medical emergency and is treated immediately with epinephrine.
Because most reactions begin within about 30 minutes of an injection, allergy shots are given under medical supervision and you are observed for at least 30 minutes afterward so any reaction can be treated on the spot. Poorly controlled asthma is the single biggest risk factor for a severe reaction, which is why your breathing and asthma status should be checked before each dose.
Modern programs apply these same safeguards outside a traditional clinic. Curex's at-home immunotherapy, for example, supervises higher-risk injections live in a Virtual Shot Room with trained Curex clinical staff and confirms a prescribed epinephrine auto-injector is on hand at the injection location before dosing. Whichever setting you choose, talk with a clinician about your personal risk factors — especially asthma — before starting treatment.
The key points
The handful of things that decide the answer — skim these if you only read one section.
Local reactions are most common
Redness, warmth, swelling, and itching at the injection site are expected, usually appear within hours, and fade within a day; a cool compress, antihistamine, or topical steroid helps.
Systemic reactions are less common
Whole-body symptoms like sneezing, nasal congestion, hives, coughing, or throat tightness can occur and should be reported to your provider right away.
Anaphylaxis is rare but serious
A severe, life-threatening reaction with trouble breathing, swelling, and dizziness is uncommon but requires immediate epinephrine and emergency care.
Most reactions happen within 30 minutes
This is why shots are given under supervision and you must wait and be observed for at least 30 minutes after each injection.
Uncontrolled asthma is the main risk factor
Poorly controlled or unstable asthma greatly raises the risk of a severe reaction, so asthma status and breathing are checked before each dose.
Please read before acting on this
General information — not medical advice
This page is a general research summary about the medication in question. It does not account for your specific health, other medicines you take, or your dose, and it can go out of date. It is not medical advice, a prescription, or a substitute for professional judgment.
Ask your pharmacist or prescriber before starting, stopping, changing, or continuing any medication — they can check it against your situation in minutes.
Frequently Asked Questions
Mild local reactions — redness, swelling, and itching at the injection site — are very common, occurring in a large share of injections. Systemic whole-body reactions are far less frequent, and anaphylaxis, the most severe reaction, is rare. The overall safety record of allergen immunotherapy given under supervision is strong.
A typical local reaction appears within a few hours and usually settles within 24 hours; a cool compress and an oral antihistamine can ease it. Systemic symptoms generally begin within 30 minutes, which is why you are observed at the office. Report any reaction that is large, spreading, or slow to resolve.
A small area of redness, warmth, and swelling is a normal local reaction. Apply a cool compress and consider an oral antihistamine, and mention it before your next dose so the size can be tracked. Seek urgent care for widespread swelling, hives, trouble breathing, or dizziness, which may signal a systemic reaction.
Yes, but it is rare. Anaphylaxis is a severe, whole-body allergic reaction that can cause trouble breathing, swelling, and a drop in blood pressure, and it needs immediate epinephrine. Because most reactions start within 30 minutes, shots are given under supervision with a 30-minute observation period so any emergency can be treated at once.
Reviewed by
Curex Editorial TeamReviewed for accuracy
Last reviewed August 2026
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This content is for general informational purposes only. It is not medical advice, a prescription, or a substitute for professional judgment, and it does not account for your health, other medications, or dose. Always ask your pharmacist or prescriber before starting, stopping, or changing any medication.
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