What is a cross allergy?

Many pollen allergy sufferers are not only allergic to tree or grass pollen. At the same time, certain fruits, spices or nuts are a problem for them. By definition, a cross allergy is a food allergy that is triggered by hypersensitivity to other allergens (these are the allergenic substances) such as pollen, latex or house dust mite excrement. The cause of this reaction between pollen and so-called pollen- associated foods is based on the structural similarity of the allergens in pollen and fruits .

The cross allergy is not caused by the actual allergen, but by other substances that have a similar surface structure to the allergen. The immune cells that are directed against the allergen in the birch pollen find similar binding sites in apples to which they can dock. The result is an allergic reaction cascade: The birch pollen allergy sufferer gets typical allergy symptoms when biting into the apple. Without the allergy to birch pollen, he would have no symptoms when consuming the apple.

About 60 percent of people allergic to pollen develop this cross-reaction to food. However, the cross-reaction can also occur with an allergy to house dust mites or latex. A cross allergy usually only occurs when the initial energy has manifested. This is why adults are more often affected than children. The type of pollen allergy also influences the likelihood of a cross-reaction. Cross allergies in early bloomers are particularly common. People who are allergic to birch, alder and hazel pollen often react with a cross allergy to nuts.

What happens in the body when there is an allergy?

In the case of an allergy, the immune system is directed against actually harmless substances. These so-called allergens can be plant pollen, excrement from house dust mites, medicines or animal proteins . The immune defense does not recognize that the substances are actually harmless and fights them. The first time they come into contact with the allergen, the immune cells produce so-called immunoglobulin E antibodies , or IgE antibodies for short. These are specifically aimed at the allergen and accumulate on the surface of mast cells, a special type of white blood cell.

The first contact with the allergen is usually symptom-free and is referred to as sensitization. The next time it comes into contact with the allergen, the immune system is on the alert: the IgE antibodies recognize the allergen and form a complex with it. The mast cell bursts and the messenger substance histamine is released .

This creates the typical allergic complaints. So the allergic reaction is an exaggerated immune reaction . Medical professionals also refer to diseases that are caused by this excessive immune response as atopic disease. Many patients with cross allergies also suffer from other atopic diseases (for example hay fever, asthma , neurodermatitis ).

Cross allergy: strength of reaction varies

The strength of the body's reaction to pollen-associated foods depends on various influencing factors:

• Allergen content in food: The allergen content in organic products varies depending on the variety, production region and degree of ripeness
• Cumulative effects : One type of fruit may be tolerated without discomfort, but several types, for example in a fruit salad, are not
• Preparation methods such as heating or fermenting can destroy the allergen
• Strength of the current pollen count
• Exercise can lower the reaction threshold. Do not consume suspicious foods before, after or during exertion
• Medications such as beta blockers or nonsteroidal anti-inflammatory drugs can affect the allergic reaction
• Current illnesses such as a gastrointestinal infection or a cold
• stress
• Alcohol consumption
• Hormonal factors (e.g. menstruation, pregnancy)

Cross allergy: symptoms

The intensity of the symptoms of a cross allergy can vary from person to person.

The following symptoms suggest a cross-reaction:

• Tingling on the lips
• Itching in the mouth, throat, sometime ears
• Swelling of the lips, lining of the mouth and / or roof of the mouth
• Tongue swelling
• Skin changes, blisters or hives around the mouth
• to cough

The symptoms of cross allergy are often limited to the mouth area. In rare cases, however, a severe allergic reaction affecting the entire body (anaphylaxis) can occur. Then the following complaints arise:

• Itching all over the body
• Hives and wheals all over the body
• Reddening of the skin
• Worsening of existing eczema (for example, neurodermatitis)
• Gastrointestinal complaints
• Nausea and vomiting
• dizziness
• headache
• Circulatory problems
• shock

The symptoms of cross allergy usually appear a few minutes to two hours after consuming the food. A cross allergy is usually mild and the symptoms disappear after a few minutes .

An allergy can be life-threatening: If the entire body reacts violently to the allergen, the circulation can fail and the organs are insufficiently supplied. Doctors call this condition anaphylactic shock. One possible reaction is a swelling of the larynx, which closes the airways. Also circulatory and multi-organ failure are possible consequences and can be fatal. Anaphylactic shock is therefore always a medical emergency and you should call an emergency doctor or go to a hospital immediately.

Risk factors for cross allergies

Anyone can develop an allergy and thus a cross allergy in the course of their life. There are a few factors that increase your risk. These include:

• genetic predisposition
• unhealthy diet
• excessive hygiene
• smoking
• Secondhand smoke
• Overweight and obesity

The following risk factors for (cross) allergy also occur in infants and children:

• Lack of vaccination protection : Large-scale studies have shown that the more vaccinations a child has received, the lower their risk of developing hay fever, asthma or neurodermatitis
• Failure to breastfeed infants in the first four months of life
• Avoiding potential food allergens during pregnancy / in small children: Avoiding foods that are common allergies does not protect children from possible allergies. On the contrary: There are indications that this can even have a negative effect on the development of tolerance and that the immune system is more likely to respond to harmless substances.
• Caesarean section

Diagnosis: test cross allergy

If you suspect you have a cross allergy, you should see your doctor. The family doctor is the first point of contact . If necessary, he can recommend an allergist or ear, nose and throat doctor (ENT) who will take over the allergy test and further treatment.