Desensitization

Markus Fichtl is a freelance writer in the medical department.

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Desensitization is a therapeutic method for allergies of the immediate type (= type I allergy). It is mainly used for allergies to insect venom, pollen or house dust mites. Read here how hyposensitization works, what it does and what risks it entails.

What is desensitization?

Desensitization is also called desensitization or "specific immunotherapy" (SIT). The doctor repeatedly gives the patient the respective allergy trigger (allergen such as bee venom), in slowly increasing doses over a longer period of time. In this way, the immune system slowly gets used to the allergen, and the allergy symptoms improve or even go away completely.

The name of the therapy is derived from this mode of action: "hypo" stands for "less", and "sensitization" for the development of a defense reaction of the immune system against a certain substance.

Sole causal treatment

There are basically three ways to treat an allergy:

• Exposure prophylaxis: avoidance of the allergenic substance (allergen)
• medication
• Desensitization

The first two therapy methods - exposure prophylaxis and medication - aim only to prevent or alleviate allergy symptoms. On the other hand, the desensitization takes action directly against the cause of the complaints - the hypersensitivity of the immune system to the respective allergy trigger. It is therefore the only way to treat the cause of an allergy and, in the best case, get rid of it. However, desensitization is only possible in the case of certain allergies (see below).

What happens in the body when there is an allergy?

The human immune system is designed to protect the body from harmful effects, such as bacteria and viruses. The immune system recognizes these mainly by their surface structure and, if necessary, forms defense substances (antibodies).

The same mechanism works in the case of an allergy: an actually harmless substance (such as grass pollen or nickel) enters the body through breathing, food or the skin and comes into contact with the cells of the immune system. In some people, these then start a defense reaction: antibodies are formed to fight the supposedly dangerous intruder - an allergy develops. Why some people are allergic to certain substances and others not has not yet been conclusively clarified.

The desensitization approach can best be described in this context as a kind of "exposure therapy" with the allergen.

When is a desensitization carried out?

The doctor will carry out the desensitization especially in the following cases:

• in the case of more severe allergies for which it is not enough to avoid the allergen or to relieve the symptoms with medication.
• when there is a threat of secondary diseases such as asthma, i.e. a so-called change of the allergy level from the upper to the lower airways.
• in the case of particularly frequent, unavoidable contact with the allergen (for example people who work in agriculture and are allergic to pollen or animal hair
• with severe side effects of drug therapy.

What can desensitization do?

A desensitization can

• reduce the symptoms of existing allergies, including those of insect venom allergies (especially allergy to bee or wasp venom), pollen allergy, house dust mite allergy, animal hair allergy (e.g. dog or cat allergy), mold allergy (listed according to the decreasing effectiveness of the hyposensitization).
• prevent asthma from developing.
• cure mild forms of asthma.
• prevent further allergies (additional sensitizations) from occurring.
• help to reduce the need for allergy medication.

With a desensitization, an allergy can be treated relatively safely (only slight side effects), long-term and low-risk with good success (even if there is no guarantee of success).

What do you do with the desensitization?

Depending on how the allergen is administered, doctors differentiate between two forms of desensitization:

• subcutaneous immunotherapy (SCIT): the classic hyposensitization; the allergen is injected under the skin here.
• sublingual immunotherapy (SLIT): the allergen is placed under the tongue (as a tablet) or dripped.

Subcutaneous Immunotherapy (SCIT)

Classic hyposensitization, subcutaneous immunotherapy (SCIT), is carried out by the attending physician in the allergological outpatient department. He injects a liquid, ready-made and standardized allergen mixture under the skin about a hand's breadth above the elbow. This "allergy vaccination" is repeated weekly, with the dose of the allergen being increased weekly until the individual maximum dose is reached. Once the maximum dose has been reached, it will continue to be administered at monthly intervals.

Before each dose increase, the doctor pays attention to possible side effects of the previous injection and adjusts the vaccination schedule if necessary. If necessary, he can also prescribe medication for any allergic symptoms that may occur, especially antihistamines. These inhibit the action of the body's own messenger substance histamine, which plays a key role in allergic reactions of the immediate type.

Duration of desensitization

The success of the classic hyposensitization, the duration and frequency of allergen administration vary from person to person and depend on the underlying allergy. The average duration of treatment is three years, for wasp venom allergy three to five years. In the case of bee venom allergy, the desensitization is carried out indefinitely - the doctor must regularly administer a "maintenance vaccination" over the long term.

The doctor and patient can jointly decide to end the treatment when the allergy symptoms and the need for allergy medication have decreased sufficiently (for example during the last pollen season).

The doctor can also do a skin test with the relevant antigen and take blood from the patient to determine the immune reaction: In an allergic reaction, so-called immunoglobins E (IgE) are found in the blood. This class of antibodies play an important role in triggering allergic reactions. If your blood level has decreased or has returned to normal, the desensitization is considered to have been successfully completed.

Sublingual Immunotherapy (SLIT)

In this form of hyposensitization, the allergen is applied under the tongue as a liquid solution or as a tablet. This method has fewer side effects than the "allergy vaccination" (subcutaneous desensitization, SCIT). However, their effectiveness has not been proven in studies as extensively as that of the SCIT.

What are the risks of desensitization?

Overall, desensitization is a very safe process. Side effects can of course be allergic reactions such as sneezing, tearing, swelling or itching. In order to observe how the patient reacts, he usually has to stay in the practice for half an hour after each therapy session. He should also avoid physical activity and alcohol on the day in question.

Especially in the initial phase of subcutaneous immunotherapy, mild side effects such as redness, swelling, itching, wheals and tiredness occur very often at the injection site. If these symptoms are more severe, the doctor usually prescribes medication (such as antihistamines) and reduces the dose of the next "vaccination".

More severe but easily treatable side effects that are possible with a desensitization are, for example, wheals all over the body (urticaria = hives) or swelling in the neck area (Quincke's edema, angioedema).

The most serious possible side effect of desensitization is anaphylactic shock - the most severe form of an allergic reaction. It is rare, but can lead to respiratory and circulatory arrest. In the practice, appropriate emergency medication is always available for this emergency.

What do I have to consider when desensitizing?

Hay fever (pollen allergy) is often caused by different allergens, i.e. different types of plant pollen. The more there are, the worse the success rate of desensitization. Therefore, the doctor combines a maximum of three different allergens in the therapy - generally they should be related allergens with a similar structure.

The most common exclusion criteria from desensitization are:

• Pregnancy before the start of desensitization, as the strength of the immune reaction and its influence on the fetus cannot be predicted sufficiently. However, if the expectant mother has already started the desensitization before the pregnancy and tolerated it well, she can continue it during the pregnancy.
• Cardiovascular disease or use of beta blockers
• severe autoimmune diseases
• uncontrolled asthma
• Vaccination less than two weeks ago
• current infection

Desensitization in children

Desensitization works best in youth. The success rate tends to decrease with age. Doctors therefore recommend early school age for initial treatment, but not before the age of five.

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