Runny nose, sneezing, itchy eyes, fatigue, headaches. Those who endure hay fever know these symptoms all too well.

When allergies occur this time of year, they’re usually due to an allergic sensitivity to airborne mold spores or to pollens from grass, weeds and trees.

But for people who already suffer with hay fever, under certain conditions, an attack can be set off even in the absence of pollen. The trigger? Your brain…

A Conditioned Response

The first recorded instance of a brain-triggered allergy attack occurred back in 1886, when a person with asthma viewed an artificial rose and suffered an allergic attack.

Later, the work of Ivan Pavlov, best known for demonstrating conditioned reflex through his famous study with dogs, was able to show that immune responses can also be conditioned.

This means, for instance, that if a person associates a dust mite allergy with a particular odor, then the same smell will trigger an immune reaction even though no dust mite is present.

Despite the early research, it wasn’t until decades later, in the 1970s, that the interaction between behavior, the brain, and the immune system became an established field of research called psychoneuroimmunology.

Since then, researchers have found that placebo responses in patients with allergies are among the strongest observed in clinical studies, and strong psychological factors are apparent in people with a vast array of allergic disorders.

A Specific Environment Sets Off Symptoms

Behavioral neurobiologists from the University of Tübingen, Germany, conducted a series of experiments in volunteers who suffered hay fever.

Each entered a test room where they were given a nasal spray containing the allergens that set off their attacks.

Later, the experiment was repeated in the same test room. This time however, there were no allergens in the nasal spray, although the participants were told there was a 50 percent chance it contained pollen.

Even so, by being in the same environment, some had an allergic reaction shown by a rise in tryptase, an enzyme that’s produced at a higher level when mast cells within the immune system are activated in response to an allergen.

Re-encountering the specific environment, even in the absence of allergens, was all it took to trigger a conditioned allergic reaction.

Study leader, Dr. Luciana Besedovsky wrote, “Our findings suggest if someone goes to a place where they usually have hay fever, like a park with lots of trees, they might have an allergic reaction.

“This might happen outside of pollen season because they have been mentally conditioned to associate that park with hay fever.

“It is astonishing how quickly the immune system learns the mismatched reaction. In the experiment, a single allergen dose was sufficient to link the allergic reaction with the environment.”

The Importance of Sleep

For more than a decade, the research group studied the relationship between sleep and the immune system to investigate whether sleep was involved in storing the memory that linked the environment with the allergic reaction.

To test this idea, they carried out a new experiment. Participants were given the nasal spray containing the allergens in the evening. Half the group slept during the night while the other half were kept awake until the following evening.

Then, a week later, after entering the same test room, the group was given the nasal spray without the allergens. The only ones to experience hay fever symptoms were those who had slept.

A week later, the group that had reacted was sent into a different test room. This time they were symptom free.

Another study author, Professor Jan Born, explained, “Just as in a conventional learning process, the sleep phase played a decisive role in our study. Only through sleep did the brain firmly connect a certain environment with an allergic reaction.”

The researchers believe the hippocampus, a key memory and learning center, plays a role in conditioning a person to respond to their environment. What’s more, they believe that sleep is needed to free up the hippocampus for new memories.

Hay Fever is Not Imaginary

Dr. Besedovsky wants to assure sufferers that hay fever is not all in the mind. “We are not suggesting anyone makes up having hay fever, as it is a biological process, but this does suggest the immune system responds to certain cues and environments.”

While this study is the first experimental proof that a specific location alone can trigger an allergic reaction, and that sleep is required to form the association, the news is not of much help to allergy sufferers.

As Dr. Besedovsky admitted, we all have to sleep.


  1. https://www.pnas.org/content/117/20/10983
  2. https://uni-tuebingen.de/en/university/news-and-publications/newsfullview-news/article/being-
    in-the-wrong-place-can-set-off-an-allergic-reaction/
  3. https://www.thesun.co.uk/news/health-news/11561351/hayfever-may-be-in-the-mind/

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