What if there is a link between seasonal allergies and depression?

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Atlantic : Some American researchers are now working on the potential connection between seasonal allergies and certain mental disorders, such as depression or anxiety. How to explain a link between two apparently so different pathologies? What role can allergies play on mental health?

Madeleine Epstein : There are two things to mention. Let us remember first that patients often tend to devalue themselves when they do not feel well. Everything becomes more difficult and in some cases it can be a slope that can lead to depression. However, it is important to specify that, as with all pathologies, depression is multi-factorial: a simple allergy will never be enough to get there. This is also true for Covid, for example: why does 10% of the population suffer from lasting symptoms when the rest are preserved? In this case, there is often a predisposition and an addition of factors that make this kind of progression of the disease possible.

Therefore, it is not possible to extrapolate a potential link between allergy and depression to the entire population. Not all allergy sufferers risk ending up depressed. This scenario, that the New York Times otherwise described very well, is still unknown. It probably exists but it is rarely highlighted

The other important element to mention is more technical: these are cytokines, these are proteins which intervene during the reactions of the immune system in the event of infection, or allergies and which can activate certain areas of the brain responsible for regulating depression and anxiety. In any case, this is the theory that the authors of the article are trying to demonstrate.

To fight against certain allergies, the body produces certain types of proteins, which can sometimes cause other problems in terms of depression or anxiety, analyze several of the researchers who defend this theory. Does this mean that all allergies would (theoretically, at least) carry the same risk of mental disorder? What do we currently know about the potentially most dangerous infections?

Attention ! Cytokines and interleukins do not work in one direction. Some indeed induce an inflammation (of allergic type, for example), when others come on the contrary to block it. These are extremely subtle and fascinating mechanisms, about which our knowledge remains limited even if we now know more and more. The interactions are many and varied.

This does not mean, however, that we can make a difference between an allergy to cats or an allergy to pollen, which is moreover the only one to have been tested, when it comes to establishing a link with depression. From the mechanism mentioned by the researchers, we can assume that the origin of the allergy does not change anything. It is the mechanism triggered following contact with the allergen that counts. It’s like when you take an antihistamine: the drug doesn’t know what the patient is allergic to… and yet it works all the same, whatever the origin of the allergic reaction.

If this theory, following new studies, were proven, it would seem logical that the correlation (provided it is proven, once again) also applies to other sources of allergy.

If this theory were verified and relevant, what would this imply in terms of treatments for allergies, but also for depression?

Let us first recall that this theory, however interesting it may be, has not yet been confirmed. For now, only the correlation between depression and pollen allergy has been analyzed. The subject of the tests was not human: it is a mouse.

Assuming that this theory is correct, that is to say, assuming that it is proven after having been the subject of additional studies, it would imply that allergy is a path to depression. We can then think that by treating the allergy upstream, it would be possible to avoid depression.

This would be a fantastic prospect, especially on the side of allergists: we regularly come up against our health authorities who remind us that allergic rhinitis is not a public health problem, to justify a possible desensitization treatment reimbursement. If the link between allergy and depression were proven, the situation would be different.

Moreover, whatever the relationship between allergy and depression, it would always be useful to work on the development of better treatments. The room for improvement is real. Of course, we must not lose sight of the fact that depression could not be treated simply by treating the allergy. In many cases, the link (provided it exists, once again) would not be unambiguous.

Moreover, no symptom is specific to allergy, which means that a check-up is always necessary to confirm a suspicion of allergy. Likewise, there is not just one form of depression…

When should allergy sufferers consider seeking treatment if they feel they are suffering from such symptoms?

Ideally, the level of treatment should be adjusted to the severity of the symptoms. The goal is not to limit the consumption of drugs, but to allow the patient to get better. It is necessary to be treated as soon as the symptoms are embarrassing or are likely to become so. If the treatment proves to be insufficient, it is necessary to consult, to adapt the treatment.