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How does allergy immunotherapy (desensitisation) work?

Allergy immunotherapy – sometimes called desensitisation – is a medical treatment that helps retrain the immune system to react less strongly to specific allergens. The treatment involves giving very small, gradually increasing doses of the allergen, either as injections (subcutaneous immunotherapy) or as tablets that dissolve under the tongue (sublingual immunotherapy). Over time, this helps reduce allergic symptoms and can even prevent severe reactions.

Immunotherapy is most often used for conditions such as allergic rhinitis (hay fever), allergic asthma, and insect sting allergy. It is also used for certain food allergies, such as peanut, tree nut, milk and egg allergies, particularly in specialist allergy clinics.

Clinical trials have shown that allergy immunotherapy can provide long-term relief from allergic symptoms, reduce the need for daily medication, and even lower the risk of developing new allergies or asthma. For many children with severe allergic symptoms, immunotherapy can be a life-changing, effective treatment.

A brief history of allergen immunotherapy

Immunotherapy was first used about 100 years ago. In 1911, Leonard Noon and John Freeman developed a novel allergy treatment : injecting pollen under the skin of people with hayfever, to desensitise the immune system by encouraging the body to build immunity to it.

By the 1930s, this type of desensitisation had become a recognised and widely used medical treatment. Over time, medications such as antihistamines, decongestants, and steroids were developed to manage allergy symptoms. While these treatments are invaluable, they only relieve allergy symptoms rather than addressing the cause.

Allergy immunotherapy works at the source of the allergy by retraining the immune system, offering longer-term relief rather than temporary symptom control. Immunotherapy is now used worldwide as a safe and effective treatment for a range of allergic conditions.

How successful is immunotherapy?

The patients I have treated with immunotherapy report improved symptoms and reduced use of traditional treatments, such as antihistamines and nasal steroid sprays.  Using immunotherapy from an early age may prevent new allergies from developing and reduce the likelihood of getting asthma, which we know is 8 times more likely in children who suffer from hayfever.

What are the different ways of performing desensitisation?

Subcutaneous immunotherapy (SCIT):

This treatment involves a course of injections designed to gradually desensitise the patient to allergens. It is currently available for grass and tree pollen allergies. Treatment consists of six injections given over six weeks before the pollen season each year, for a total of three years. SCIT has been shown to be highly effective and is suitable for many patients with severe hay fever.

However, there is a small risk of serious allergic reactions, particularly in children with asthma, which means this treatment is not suitable for asthmatics. For safety reasons, SCIT is administered only in a hospital setting under close supervision, with each injection followed by 1 hour of observation.

Sublingual immunotherapy (SLIT)

This treatment involves placing an allergen extract under the tongue, either as tablets or drops. It is considered very safe, with severe reactions being rare. The first dose is always given under medical supervision. Because of its safety profile, SLIT is more suitable for children with well-controlled asthma.

After the initial dose, treatment is taken daily at home for three years and has been shown to provide long-term changes in the immune system.

About your immunotherapy journey

Your immunotherapy journey will start with a visit to the allergy clinic, where your child’s symptoms and medical history are carefully reviewed. Diagnostic tests will be used to identify the specific allergen causing the reaction. Once we know what is causing the allergic reaction, the treatment involves administering regular doses of an allergen extract to reduce symptoms.

Most children experience only mild allergic reactions, such as redness or swelling at the injection site, especially in the early stages. Serious allergic reactions are infrequent, but I will monitor your child closely and make sure you know what to do in case of any problems.

There is an increasing body of research examining how the treatment affects the immune system.  It has been shown that regular exposure to the allergen at a level below that which elicits a reaction leads to the production of an antibody called IgG4.  This antibody blocks IgE, the antibody responsible for causing allergic reactions.

The effects of immunotherapy can last for many years after the treatment is complete.  The therapy offers long-term benefits, particularly for children, as it has been shown to prevent the development of additional allergies and asthma symptoms. Immunotherapy can also reduce reliance on medication, or – at the very least – mean less worry about accidental exposure.

Note that desensitisation treatment should only be administered under the guidance of a trained medical professional.

What are the benefits of allergen immunotherapy?

Scientific studies have shown that immunotherapy can reduce symptoms of a range of allergies.  The treatment can be so effective that many patients report needing to use less or no medication.  As the immune response is altered, the beneficial effects last longer than the time taken to deliver the treatment.

If treatment is started at an early age, then it may prevent new allergies from developing.  It is important to note that immunotherapy only works against a specific allergen and will not improve symptoms caused by other allergens.

Are there any side effects of immunotherapy?

As with all medications, immunotherapy can potentially cause side effects, and in the early stages of the treatment, it is common to experience the following within a few minutes of taking the dose:

• Mouth itching
• Irritating sensation

In most cases, this settles within 20 minutes of starting treatment, but can be alleviated with over-the-counter antihistamines.

Other side effects affect up to 1 in 10 people.  These tend to occur in the first week of taking the medication and are generally mild to moderate and short lived:

• Eye or ear itching
• Numbness of skin, mouth or tongue
• Asthma symptoms
• Eye, nose or mouth inflammation
• Cough or sneeze
• Shortness of breath
• Nasal discomfort
• Dry throat
• Swelling of lips or tongue
• Stuffy or runny nose
• Mouth blisters
• Stomach pain or discomfort
• Heartburn
• Tiredness
• Itching
• Chest discomfort
• Fever

Can immunotherapy be used for hay fever?

Modern immunotherapy was developed to ease hayfever symptoms – and it is still used for this purpose.  We offer immunotherapy for airborne allergens such as grass and house dust mite.  When it comes to this type of airbourne allergen, immunotherapy is recommended for patients over five years old who, despite allergen avoidance and maximum recommended medication, still have uncontrolled symptoms. The (sublingual) immunotherapy involves a small, dissolvable tablet or a solution being placed under the tongue each day. The tablets/solution contain tiny amounts of either grass pollen or house dust mites, helping your child’s immune system build a tolerance to the allergen.  The treatment lasts three years. During that time, the patient must continue regular allergy medication.  The aim is that by the end of the treatment programme, the symptoms and reliance on medication have reduced.

How is immunotherapy used for food allergies?

Oral Immuno Therapy (OIT) — also known as oral desensitisation — is a treatment that helps children become less sensitive to a food they are allergic to. It works by giving very small, carefully measured amounts of the allergenic food and slowly increasing this over time.

The aim is to help your child tolerate the food better, so that accidental small exposures are much less likely to cause a reaction. This can offer families greater confidence and peace of mind, especially with severe allergies.

OIT has been most widely studied for common food allergies such as milk, egg, tree nut and peanut. Palforzia, a peanut-based capsule, was the first licensed therapy and opened the door to oral immunotherapy for peanut allergies.  Peanut allergy desensitisation can now be done using alternative products.

Which food allergies can be treated with immunotherapy?

Most research has been done on desensitisation to milk, egg, tree nut and peanut.  We have been offering desensitisation to milk and egg on the NHS for some time, but can also offer desensitisation to peanuts.

My child has a nut allergy — will immunotherapy work for them?

Every case needs to be considered by an expert. I previously offered desensitisation to peanuts using Palforzia® (discontinued in July 2026), the first treatment licensed for peanut desensitisation in children. Peanut allergy desensitisation can now be done using alternative products. Desensitisation works by gradually increasing the body’s tolerance to peanuts through a method called oral immunotherapy (OIT). For people with peanut allergies, which are often severe, the treatment is often used to reduce the risks of accidental exposure. Gradual exposure should not be tried at home.

How long does the process for food immunotherapy take?

This will depend on which food immunotherapy is being given. Some are faster than others, but a typical protocol takes 8-20 weeks. The doses are increased with specific gaps between doses, but reactions or other factors, such as incidental illness or missed doses, may require a longer gap between doses.

Once we have reached the top dose (maintenance), the patient needs to continue to take this regularly to maintain the effect.  The frequency of this dosing can be reduced, but not stopped, over time without apparent loss of effect.

Although a child may be suitable for immunotherapy, it may still not be the right treatment option for them. If your child struggles with severe allergic symptoms, or if you’re worried about the impact of allergies on their daily life, a consultation can help you explore whether immunotherapy is the right option.

For many patients, continuing to avoid the allergen and maintaining an appropriate emergency action plan are the most effective ways to manage the allergy.

To decide whether immunotherapy is right for your child, we use an important process of shared decision-making, together with detailed information about the treatment, to determine whether it is the right choice.