Allergen Immunotherapy (Allergy Shots)

Allergen immunotherapy, commonly called allergy shots, is a long-term treatment that gradually trains the immune system to stop overreacting to the substances that trigger a patient's allergies.

In a normal allergic reaction, the immune system treats a harmless substance — such as pollen, dust mites, or pet dander — as a threat and releases chemicals that cause sneezing, itching, or swelling. With allergy shots, a doctor injects tiny, carefully measured amounts of the allergen (the trigger substance) under the skin at regular intervals. Over time, the dose is slowly increased. This process teaches the immune system to become tolerant — meaning it learns to ignore the allergen instead of attacking it. Most patients notice their symptoms become less severe and less frequent as treatment progresses.

Allergy shots are used when a patient's allergy symptoms are difficult to control with medication alone, or when avoiding the trigger substance is not practical in daily life. An allergist (a specialist in allergies and the immune system) will first confirm which specific allergens are causing the symptoms through skin or blood tests before recommending this treatment.

• Allergic rhinitis (hay fever) — sneezing, runny nose, and nasal congestion triggered by pollen, mold, dust mites, or animal dander
• Allergic asthma — breathing problems and wheezing that are worsened by allergen exposure
• Allergic conjunctivitis — itchy, watery, or red eyes caused by airborne allergens
• Insect venom allergy — severe or systemic reactions (reactions that affect the whole body) after bee, wasp, or hornet stings
• Atopic dermatitis (eczema) — in selected cases where a clear allergen trigger has been identified

Allergy shots are not suitable for everyone. Doctors will generally advise against this treatment in certain situations.

• Severe or unstable asthma that is not well controlled with current medication
• Serious heart conditions or the use of certain heart medications that could interfere with emergency treatment if a reaction occurs
• Active autoimmune disease (conditions where the immune system attacks the body's own tissues)
• Pregnancy — immunotherapy is usually not started during pregnancy, though it may be continued if already underway
• Children under five years of age, in most centres
• Patients who are unable to commit to the regular, long-term schedule of injections

Allergy shots are generally considered safe when given in a medical setting with trained staff present, but like any treatment that involves the immune system, they do carry some recognised risks.

• Local reactions at the injection site — redness, swelling, and itching around the area of the shot; this is the most common response and usually settles within a few hours
• Systemic reactions — sneezing, nasal congestion, hives (raised itchy welts on the skin), or mild wheezing that affect areas beyond the injection site
• Anaphylaxis (a severe, whole-body allergic reaction) — rare but serious; this is why patients are observed in the clinic for at least 20–30 minutes after every injection
• Worsening of asthma symptoms shortly after an injection
• Build-up of discomfort if doses are increased too quickly — the schedule is designed to minimise this
• Prolonged course of treatment — full benefit usually requires several years of regular injections, and some patients do not respond as well as others

Before starting allergy shots, the doctor needs to confirm exactly which allergens are causing the patient's symptoms. Preparation involves allergy testing, a review of overall health, and a few practical steps on the day of each injection.

Before the treatment course begins, the following tests or assessments are typically carried out.

• Skin prick test — small amounts of common allergens are placed on the forearm or back, and the skin is lightly pricked to check for reactions
• Intradermal skin test — a small amount of allergen is injected just under the skin surface for a more sensitive result, if needed
• Specific IgE blood test — a blood sample measures the level of allergy antibodies (proteins that trigger allergic reactions) against particular allergens
• Lung function test (spirometry) — for patients with asthma, to check that breathing is stable enough to begin treatment
• General health review — the doctor will check current medications, existing conditions, and pregnancy status

On the day of each injection, there are a few things patients are usually asked to consider. Strenuous exercise should be avoided for a couple of hours before and after the shot, as physical activity can increase blood flow and raise the risk of a systemic reaction. Patients should inform the clinic if they are feeling unwell, have a fever, or if their asthma has been poorly controlled recently. No fasting is required. There are no specific food or drink restrictions before allergy shots.

Some medications may need to be discussed with the doctor before starting, including blood thinners or certain heart medications, as these can affect the safety of emergency treatment if a serious reaction occurs. The doctor will advise on this individually.

The treatment itself follows a structured sequence.

• 1. The clinic prepares a personalised vial of allergen extract, formulated specifically for the patient based on their test results.
• 2. The patient checks in and informs staff of any recent illness, new medications, or reactions since the last visit.
• 3. A nurse or doctor injects a small amount of the extract under the skin, usually in the outer upper arm.
• 4. The patient remains seated in the clinic for an observation period — typically at least 20 to 30 minutes — so staff can monitor for any early signs of a reaction.
• 5. If no significant reaction occurs, the patient is cleared to leave and is given the date for the next injection.
• 6. Over the build-up phase (usually spanning several months), the dose is gradually increased at each visit.
• 7. Once the target dose is reached, the patient enters the maintenance phase, where the same dose is repeated at longer intervals — often every two to four weeks — for several years.

Because allergy shots are given repeatedly over a long period, aftercare is an ongoing routine rather than a single recovery episode. The most important safety step happens immediately after each injection: staying at the clinic for the required observation period so that any early reaction can be treated promptly. Once that window has passed without incident, patients can return to their normal daily activities.

• Avoid vigorous exercise for at least a few hours after each injection, as this can increase the chance of a delayed reaction.
• If the injection site is red, swollen, or itchy after leaving the clinic, applying a cool compress usually helps; the doctor will advise on whether any medication is appropriate.
• Inform the clinic before the next visit if any unusual symptoms — such as hives, wheezing, or a rash — developed after a previous shot, even if they seemed mild.
• Keep all scheduled appointments; missing injections or extending the gap between doses can mean the dose needs to be reduced and the build-up phase repeated.
• Continue taking any regular allergy or asthma medications as directed by the doctor — allergy shots work alongside these, not instead of them, especially in the early months.
• Regular follow-up appointments with the allergist allow the doctor to assess progress, adjust the maintenance dose if needed, and decide when treatment can eventually be tapered or stopped.
• Most patients continue maintenance injections for three to five years; the allergist will evaluate whether lasting tolerance has developed before recommending any change to the schedule.