Allergic reactions can occur without a triggering allergen

Allergic reactions can occur without a triggering allergen

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Allergic reactions: sleep plays a crucial role

Almost every third adult in Germany suffers from an allergy. Those affected have symptoms such as coughing, sneezing, reddening of the skin, itching or rash after direct contact with the allergy trigger. However, allergic reactions can also occur without the triggering allergen.

According to a recent release, a research team from the University of Tübingen has deciphered the mechanism of learning mismatched allergic responses to a neutral environment and the crucial role of sleep. Their results were published in the journal "Proceedings of the National Academy of Sciences" (PNAS).

Complaints usually appear immediately after contact

According to the allergy information service of the Helmholtz Zentrum München - German Research Center for Health and the Environment, the number of people with allergies in western industrialized countries has increased 20-fold in recent decades.

In Germany, almost a third of adults between the ages of 18 and 79 have had any allergy diagnosed by a doctor.

As the Institute for Quality and Efficiency in Health Care (IQWiG) explains on the portal "", allergic reactions occur most frequently on the respiratory tract, skin and mucous membranes.

According to the experts, the complaints usually appear immediately after contact, sometimes only after hours or days.

Influence of psychological factors on allergic reactions

Allergic reactions can also occur without the triggering allergen such as grass or birch pollen if the allergy sufferer returns to the same spatial environment in which he or she was previously exposed to the allergen.

Such conditioning - learning a conditional reaction to a neutral and harmless situation per se - only happens after a sleep phase that follows the conditioning.

This is the result of a new study on the influence of psychological factors on allergic reactions, which a research team led by Dr. Luciana Besedovsky and Professor Jan Born from the Institute for Medical Psychology and Behavioral Neurobiology at the University of Tübingen.

The results can at least partially explain why allergic symptoms are so often observed in a kind of placebo reaction without the presence of the allergen.

Allergic rhinitis without allergens

For the study, subjects with allergic rhinitis were recruited, who were confronted with their respective allergen such as grass or birch pollen in a neutral test room by administering a nasal spray.

The strength of the allergic reaction occurring in all participants was measured in each case by the amount of a certain enzyme in the nasal secretion. Half of the subjects went to sleep for eight hours after this experiment, the second half had to stay awake until the following evening.

The experiment was repeated a week later in the same test room - only this time no allergens were administered.

“The subjects reacted shortly after entering the test room with an allergic runny nose. But only from the sleeping group, ”explains Besedovsky.

The test participants in the guard group would neither have reacted allergically to the return to the test room, nor would any other place to which the test subjects of the sleep group were taken in the second week would have had such an effect.

Sleep phase played a crucial role

“As with classic learning processes from other contexts, the sleep phase played a crucial role in our study. This is the only way the brain can link a specific environment to an allergic reaction, ”says Jan Born.

According to the announcement, this is the first evidence that a specific location alone can trigger an allergic reaction. The researchers assume that, as in many memory processes, the brain structure of the hippocampus is involved in environmental conditioning. This works sleep-dependent.

“It's amazing how quickly the immune system learns the mismatched response. In the experiment, a single allergen dose was enough to link the allergic reaction to the environment, ”explains Besedovsky.

The fact that this learning mechanism could be deciphered helps both allergy and sleep research. However, simple conclusions to improve the situation of allergy sufferers are difficult because you cannot do without sleep - especially since this has a positive effect on other, helpful immune reactions. (ad)

Author and source information

This text corresponds to the requirements of the medical literature, medical guidelines and current studies and has been checked by medical doctors.


  • University of Tübingen: The wrong place can trigger an allergic reaction, (accessed: May 6th, 2020), University of Tübingen
  • Luciana Besedovsky, Mona Benischke, Jörg Fischer, Amir S. Yazdi, Jan Born: Human sleep consolidates allergic responses conditioned to the environmental context of an allergen exposure; in: Proceedings of the National Academy of Sciences, (published: 04.05.2020), Proceedings of the National Academy of Sciences
  • Helmholtz Zentrum München - German Research Center for Health and the Environment: Allergy Information Service: How common is hay fever ?, (accessed: May 6, 2020), Allergy Information Service
  • Institute for Quality and Efficiency in Health Care (IQWiG): Allergies, (accessed: May 6, 2020),

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