Allergen immunotherapy
Regular, controlled doses of an allergen, by injection or under the tongue, retrain the immune system so allergy symptoms ease for years.
Allergen immunotherapy (desensitisation) is the only allergy treatment that changes the immune response instead of just blocking symptoms. A standardised extract of the allergen the patient reacts to (pollen, house dust mite, animal dander, mould, insect venom) is given repeatedly in rising and then steady amounts. Over months the body makes blocking antibodies and the allergic response quietens. It is given by injection under the skin (subcutaneous, «allergy shots») or as tablets or drops under the tongue (sublingual). Because it uses the very substance the patient is allergic to, it can trigger allergic reactions, including anaphylaxis.
How it works
Small, repeated amounts of the allergen shift the immune response away from the IgE-driven allergic reaction: the body produces antibodies that block the allergen before it can trigger symptoms. Improvement is gradual, usually after several months, and the need for allergy medicines falls. In some people it may also prevent new allergies and reduce asthma symptoms, and relief can last for years.
Subcutaneous immunotherapy («allergy shots»)
Injections are given in the upper arm in a clinic. During the build-up phase the dose rises with frequent visits over several months; in the maintenance phase injections are spaced out and continue for several years. It can be prepared for several allergens at once, including insect venom. Adults and children from about five years can receive it.
Sublingual immunotherapy
The allergen extract is held under the tongue as a dissolving tablet, generally once a day at home. Each tablet product covers one allergen or allergen group, such as grass pollen, ragweed or house dust mite. The first dose is taken in a doctor's office to watch for a reaction, and pollen tablets are started weeks to months before the pollen season.
Risks and safety
- Local reactions: redness, swelling and itching at the injection site, or mild nasal stuffiness
- Anaphylaxis, rare but life-threatening: patients wait in the office for about half an hour after each injection, and reactions are treated there at once
- Epinephrine is the first treatment for anaphylaxis; antihistamines given beforehand may reduce local reactions but do not prevent anaphylaxis
- Sublingual tablets carry a boxed warning for severe allergic reactions
Who should not start it
- Severe or uncontrolled asthma
- Significant heart disease
- People taking certain medicines, such as beta-blockers or ACE inhibitors
- Pregnancy: it is not started, although treatment begun before pregnancy may be continued
- Food allergy is not an indication for allergy shots
Test yourself
Think of the answer, then tap the question to see it.
What makes allergen immunotherapy different from antihistamines and nasal corticosteroids?
It changes the immune response to the allergen, so benefit can last after treatment stops, instead of only blocking symptoms.
What are the two phases of subcutaneous immunotherapy?
A build-up phase with rising doses over months, then a maintenance phase with spaced injections for several years.
Why do patients stay in the clinic after an allergy shot?
To watch for anaphylaxis, the rare but life-threatening reaction, and treat it at once with epinephrine.
Why is the first sublingual tablet taken in a doctor's office?
Serious allergic reactions can occur, so the first dose is supervised.
Which medicines are a reason to reconsider starting allergy shots?
Certain heart and blood-pressure medicines, such as beta-blockers and ACE inhibitors.
Example drugs
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Allergy shots: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2025); Sublingual Immunotherapy (SLIT) Allergy Tablets (American Academy of Allergy, Asthma & Immunology (AAAAI), 2026); Allergies (NHS, 2026).
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Representative model, for educational purposes only.