What happens in my body when I have an allergy?

Basically the same processes occur with an allergy as in a normal immune response. The immune system identifies an intruder as dangerous and throws various mechanisms into gear in order to get rid of the troublemaker. Unlike with a ‘real’ ailment such as a cold, an allergic reaction causes a problem when the body treats harmless substances such as pollen or food ingredients as if they were dangerous and activates its defences. What happens differently in allergy sufferers? And why does the immune system make this mistake?

An allergen, such as pollen, comes into contact with the skin or mucosa. Peptides are released. (Charitee-allergie-2-06).

These tiny protein chains dock onto IgE antibodies (Charitee-allergie-2-08), that have previously bound to a mast cell. The mast cells are located in places where the body frequently comes into contact with allergens: in the skin, the airways or the gut.

Histamine is stored in mast cells (Charitee-allergie-2-07). This is a substance that plays an important role in inflammatory processes. Whenever an allergen binds to the attached IgE antibodies, the mast cell immediately releases the stored histamine and other inflammatory messengers.

The released inflammatory substances then cause swelling of the skin, the production of secretions, itching, hives, or a narrowing of the airways.


How quickly symptoms appear depends on the type of allergy

Allergy science has defined four different types of allergic reactions or hypersensitivity (types I to IV). Types I to III are immediate hypersensitivity reactions and are triggered by antibodies (immunoglobulin, abbreviation: Ig). Type I is the most common reaction type. Hay fever, some food allergies and allergic asthma all trigger type I hypersensitivity reactions. IgE antibodies play an important role in these reactions.

In healthy people, IgE antibodies are only present in small amounts.

People with allergies have an excess of IgE antibodies. The IgE antibodies tend to bind to the surfaces of other cells. One of its preferred landing places is called the mast cell. It stores messenger substances that trigger inflammatory reactions. If an allergen then binds to an IgE antibody, the mast cell releases messenger substances that cause inflammatory symptoms.

Illustration: Tobias Borries

Prof. Dr. med. Dr. h.c. T. Zuberbier
Last changes made: September 2019