Desensitisation (also known as immunotherapy) is the practice of administering gradually increasing doses of an allergen extract in order to reduce the symptoms of the hay fever or asthma that it causes. It was first carried out almost 100 years ago to pollens and is now in widespread use around the world as a safe and effective treatment for allergies caused by different pollens, house dust mites, cat, dog and horse. It is sometimes referred to as ‘allergy vaccination’.
What is Allergy Immunotherapy (Desensitisation)?
Allergy immunotherapy treatment, sometimes referred to as ‘desensitisation’, was first used almost a century ago and is today widely regarded as safe and effective as well as being a fully licensed treatment.
Immunotherapy is backed up by extensive scientific research and we are now able to use fully UK licenced tree and grass pollen treatments, that have gone through highly rigorous assessment to confirm both effectiveness and safety. For patients with severe hayfever symptoms caused by tree or grass pollen allergies, the treatment works by administering the patient with regular high doses of the relevant pollen extract. This dampens the immune response, which reduces the severity of symptoms and the need for medication.
While existing medications such as antihistamines and steroid based medicines can alleviate some of the suffering, symptoms continue to bother many throughout the summer months. Such patients can often benefit from immunotherapy. Immunotherapy is the only treatment which affects the underlying cause of an allergy by retraining the immune system into becoming less allergic and therefore improving symptoms significantly. As a consequence, the effect of the treatment can last for years after stopping it – a disease modifying effect that is never obtained through conventional treatments which simply suppress symptoms.
How Does Immunotherapy (Desensitisation) Work?
Immunotherapy works by administering the patient with regular high doses of an allergen extract in order to reduce allergic symptoms. This then dampens the immune response, which reduces the severity of symptoms and the need for medication.
Because the immune system has a memory, the effects of immunotherapy may continue to be felt for years after the treatment is complete. Unlike any other existing allergy treatments, immunotherapy can therefore have long term benefits and in children it has been shown to prevent the future development of additional allergies and asthma symptoms.
Allergen Tablets are placed under the tongue (sublingual) daily. Over time this reduces the reactivity to the allergen (desensitisation).
What are the benefits of allergen immunotherapy?
Large scientific studies have confirmed that immunotherapy can be used to reduce the symptoms of allergic rhinoconjunctivitis (hayfever) and seasonal asthma caused by grass or tree pollen as well as dust mite. Most patients receiving treatment also report needing to use less medication. As immunotherapy actually changes the way the body’s immune system reacts to the allergen, the beneficial effects continue beyond the 3 years that the treatment is given for.
Using immunotherapy from an early age may actually prevent new allergies developing and reduce the likelihood of getting asthma in later life. However, immunotherapy only works against a specific allergen. So, for example, having immunotherapy to grass pollen may help with hay fever symptoms during the summer (which are caused by grass pollen) but will not improve symptoms caused by other allergens such as house dust mite, during other times of the year.
There are different ways of performing desensitisation. These include:
- Subcutaneous Immunotherapy: this involves giving a series of injections to desensitise the patient. We currently do this for grass pollen, tree pollen and allergy to insect stings. With pollen allergy, the treatment involves a series of injections given over 3 weeks before the pollen season each year, for 3 years. Subcutaneous immunotherapy has been shown to be very effective and is suitable for the most severe cases of hayfever. Unfortunately, it is possible to have quite severe allergic reactions to the injections especially in children and adults with asthma and thus is becoming less commonly used. This treatment is thus not suitable for asthmatics and is also only given under careful supervision, with each injection followed by a 1-hour period of observation.
- Sublingual Immunotherapy: Recent advances have meant that immunotherapy can now be given without injections. Instead, the allergen extract is given under the tongue either by tablets or drops. This method is very safe and severe reactions are extremely rare although the first dose of treatment is still given under careful medical supervision. This makes it a more suitable treatment for asthmatics, as long as their asthma is well controlled. Whilst sublingual immunotherapy avoids the need for injections it does need to be taken on a daily basis either all year or through the whole pollen season for a total of 3 years. Importantly, in both adults and children, it has been shown that a 3-year course of treatment has an effect that can last for years after the treatment has finished, confirming that it has a long term impact on the immune system. As it is a newer treatment, there is less information regarding how long the beneficial effects last after the end of treatment and how well it prevents the development of asthma, but large studies have strongly suggested a meaningful preventative effect.
Our doctors will discuss with you which type of immunotherapy may be best suited for you. Once a decision has been reached, you will be provided with more detailed information about the particular type of treatment.
Food desensitisation is an area of increasing interest and we are already using this in our practice (eg for peanut, sesame, treenut, wheat, milk and egg allergy).
How Does Immunotherapy (Desensitisation) Help Hay Fever Pollen Allergies?
Pollen allergy treatment via desensitsation reduces the immune response to the particular hay fever allergen (grass or tree pollen).
Daily doses of the allergen extract are given to the patient, which are taken sublingually (under the tongue), and this dampens the immune response and reduces the severity of the symptoms during the next hay fever period.
What Are The Side Effects Of Immunotherapy (Desensitisation)?
Like all medicines, sublingual immunotherapy can potentially cause side effects. In the early stages of treatment it is common to experience the following within a few minutes of taking a dose:
- Mouth itching
- Irritating sensation
This is a mild allergic reaction and, in most cases, settles down within 20 minutes of starting treatment but can be alleviated with simple over-the-counter antihistamines, such as cetirizine or loratidine.
Other common side effects (which may affect up to one in 10 people) include: headache
- Prickling sensation or numbness of the skin, mouth or tongue
- Eye or ear itching
- Eye, nose or mouth inflammation
- Asthma symptoms
- Shortness of breath
- Cough or sneezing
- Dry throat
- Nasal discomfort
- Stuffy or runny nose
- Swelling of lips or tongue
- Stomach pain or discomfort
- Mouth blistering
- Chest discomfort.
These generally occur in the first week of taking the medication and tend to be mild to moderate and short-lived.
What Is The Success Rate Of Immunotherapy (Desensitisation)?
Most patients receiving sublingual immunotherapy report an improvement in symptoms and less use of traditional treatments, such as antihistamines and steroid nasal sprays. In addition, using sublingual immunotherapy from an early age may actually prevent new allergies developing and also reduce the likelihood of getting asthma – which is eight times more likely in children who suffer from hayfever.
Professor Adam Fox
Date reviewed: July 2022
Adam Fox is a Professor of Paediatric Allergy with over 20 years experience in both the NHS and private sector. Professor Fox is Commercial Medical Director at Guy’s & St Thomas’ Hospitals NHS Foundation Trust and Professor of Paediatric Allergy at King’s College London and the founding Director of the KCL Allergy Academy, a postgraduate educational programme, which was a finalist at the BMJ Awards in 2018.
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