We have been blaming hygiene for our allergies for almost 40 years. Ancestral DNA has just shown that the problem is more complex
Every time a child develops a asthmarhinitis or eczema, one of the questions we ask ourselves is why it happens, and one of the ‘culprits’ we point to is excess cleaning. Right now it is a reality that we live in environments that are too neat, using disinfectant gel all the time and not letting the little ones play in the mud because logically they can get stained. However, science here has ‘traveled’ to the past to find out the origin of allergies. What have they done? Here two new and massive studies based on the analysis of prehistoric DNA are putting the famous “hygiene hypothesis“And the paradigm we face now is that the evolutionary adaptations that our immune system has developed over the last 10,000 years to survive pandemics, curiously, are designed to protect you from allergies, not to cause them. A return to the past. To understand the plot twist, we must go back to 1989 where epidemiologist David Strachan proposed the hygiene hypothesis. Here it was proposed that the lack of exposure to microbes during childhood in most modern societies deregulated the immune system, since it literally did not grow with good training under its belt. In this way, it was proposed that, by not having real pathogens to fight against, the body created an imbalance that caused the immune system itself to attack substances that are not actually a threat, such as pollen or mites. And it seemed to make sense. A genetic journey. The first blow to this hypothesis has been dealt by a great published research in Nature this same month of April. Here the researchers analyzed almost 16,000 ancient genomes from individuals who lived thousands of years ago. What they discovered here is that the transition to agriculture in the Neolithic changed everything, since human societies became dense, we began to coexist closely with animals and, with this, large-scale infectious diseases arrived. But these pathogens that we began to face, despite the many deaths they generated, also favored hundreds of immune variants to ensure our own survival. But there is more. This is where parallel research that is revolutionizing our understanding of asthma and autoimmunity comes into play. Here is an article preprint has crossed ancient DNA with the modern complete genome with the aim of looking for differences between our DNA and that of our ancestors. Logic dictated that a system “revolutionized” by evolution to fight bacterial and viral infections of the past would be the cause of today’s allergies. But the data show exactly the opposite, as the study reveals that genetic variants that were positively selected in recent millennia have strengthened defenses in “barrier tissues” such as the intestine, against pathogens, but at the same time reduce allergic inflammation. The variants. Among these defense genes We have, for example, LYZ, which codes for lysozine, a fundamental antimicrobial enzyme in our secretions that destroys part of the bacteria. We also have FUT6, which is involved in protein fucosylation, a process vital to the interaction between our mucosal immune system and the gut microbiome. Why are we allergic, then? If our genetics have been evolving for 10,000 years to protect us from allergies in the lungs and intestines, the question is inevitable: why do cases continue to increase? Here science suggests that the problem is not simply an excess of cleaning in the present, but a profound imbalance. In this way, we do not need to catch diseases or live surrounded by human society, but the problem is that our immune system, genetically adapted to the strong pathogenic pressures of the first agricultural societies, expects to encounter a series of commensal microbes in the environment. The ‘problem’ is that these microbes are no longer present in modern cities and that is why the genes we have with a protective function cannot do their job correctly. Images | Drazen Zigic on Freepik In Xataka | The allergy season in Spain has been extended by 25 days since the 90s. And 2026 brings very bad news about it
