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An allergy is an overreaction of the immune system to a usually harmless particle (the allergen) in the environment. The immune system is the body’s defense system against foreign intruders like bacteria, viruses and parasites.

What is an allergy?

It also kills damaged and sick cells like e.g. cancer cells in the body. It has many different ways to attack intruders.

In the case of allergies like hay fever (allergic rhinitis/conjunctivitis), allergic asthma and also in allergies against bee and wasp stings, it overproduces a certain kind of antibody called IgE. Antibodies are small proteins that can bind to pathogens, and depending on their kind can kill the pathogen, flag it for destruction, or call in cells of the immune system for help.

With the antibody type IgE, the antibodies bind to the allergen, and can then bind to specific receptors on cells called mast cells. These cells contain a large amount of different chemicals that cause the allergic symptoms. When the IgE binds to the mast-cells, they pour these chemicals into their environment. This process is called degranulation.
Depending on the location of these events different allergy symptoms, like runny nose and watery eyes, an asthma –attack, or blood pressure drop can be the consequence.

How are allergies treated?

Allergies can be treated symptomatically, which means the symptoms rather than the cause of the allergy are treated. Histamine is one of the chemicals secreted by mast cells. Anti-histamines inhibit the production of histamine, and therefore prevent symptoms caused by it. There are also drugs that can inhibit the degranulation of the mast cells and others that can reduce the inflammation of the airways, generalized swelling or the potentially life-threatening blood pressure drop that is associated with an anaphylaxis.

However, none of these therapies treats the cause of the allergy or tries to modify the way the immune system reacts to a ordinarily harmless stimulus. Immunotherapy tries to do exactly that.

What is immunotherapy?

Immunotherapy essentially is a vaccination with the allergen. Unlike in a vaccination against an infectious disease, where the immunization causes the immune system to react stronger to the stimulus when encountered again, in immunotherapy against allergies, the immune system learns to tolerate the stimulus.

Small amounts of the allergen are injected subcutaneously (under the skin) to an allergic person. Through slowly, but steadily increasing the dose of the allergen in the shots, the immune systems learns that the allergen is harmless. In many cases this can lead to a lasting decrease of allergy symptoms or even to complete remission. It can also prevent the development to new allergens, as people who are for example allergic to a specific sort of grass pollen often, over the years, develop an allergy to other pollen of other grass species, too. Immunotherapy can break this vicious cycle.

How is immunotherapy for allergies done?

Allergy shots require a strong commitment of the patient as they are given frequently and have to be taken over a long period of time to work. The therapy requires two phases, the build-up and the maintenance phase.

The build-up phase lasts usually from three to six months. This is phase where injections are given once or twice a week, starting with a very low concentration of the allergen. The amount of allergen in the shots is increased slowly, but steadily and reaches a plateau (the maintenance dose) after three to six months. Sometimes more rapid treatment schedules with more weekly injections that reach the maintenance dose earlier are used. The maintenance dose is different from person to person and has to be checked by the reaction to the shots during the build-up phase.

Once the maintenance dose is reached, shots are only given once or twice a month. This treatment schedule is then maintained for the next three to five years.

How long does it take to start working and does it last?

Many patients start feeling better while they are still in the build-up phase. However, for some people it can take much longer; up to a year while already on the maintenance schedule. It is also possible that the allergy symptoms are not only caused by the allergen in the shot, but by also others that were not tested for before starting the allergy shots. In this case, it can happen that the allergy shot will not help.

After three to five years on the maintenance schedule, the therapy is usually stopped by the recommendation of the treating physician. Many people have now much reduced symptoms or no symptoms at all and don’t re-develop the allergy over time. However, other people experience relapses for which a longer maintenance phase can help.

Can everybody be treated with immunotherapy for allergies?

Immunotherapy for allergies is most commonly used for people with hay fever, allergic asthma and insect sting allergies. It is not recommended for food allergies. When deciding whether you should attempt allergy shots for your allergy, you and your physician should consider the severity of the symptoms, the length of the allergy season (i.e. how long is the allergy present in the environment each year?), your response to symptomatic treatments, and whether you have the time to commit to this form of therapy.

Immunotherapy can be used for children, but people with certain medical conditions might have a higher risk for developing serious side effects, which is why the complete medical history should be discussed with the physician before starting an allergy shot regimen.

What are the risks and side effects?

Side effects of allergy shots can be local (limited to the site of infection) or systemic (all over the body). Local reactions are generally mild, occur immediately or several hours after the shot and include redness, swelling and pain at the injection site. Systemic reactions are much less common, but they can be much more serious. They usually occur within 30 min of the injection and can range from sneezing, a stuffy nose or hives to a serious systemic reaction called anaphylaxis. This is a potentially life-threatening condition with swelling in the throat, wheezing, a feeling of tightness in the chest, nausea, dizziness and low blood pressure. It responds well to medication.


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