Researchers have obtained evidence of the hygiene hypothesis: if an organism grows in sterile conditions, its level of aggressive immune cells increases, which eventually begin to attack the organism's own tissues.

There is a well-known paradox in medicine: in order to grow up healthy, a child must pass the "dirt test". More than 20 years ago, immunologists put forward the so-called hygiene hypothesis, the meaning of which is that without an external enemy, our immunity develops incorrectly. Sterile conditions, excessive cleanliness around the child do not allow his immune system to train on pathogens entering the organism: they simply do not exist. At the same time, the immune system begins to pay more and more attention to the organism's own cells, attacking them instead of the absent external pathogens. As a result, children who grew up in an exceptionally clean environment have an increased chance of acquiring autoimmune diseases such as asthma or inflammatory bowel disease.

For a long time, this hypothesis was based only on statistics. But now, thanks to research by scientists from Harvard (USA), she has more tangible evidence.