(p. A17) The idea that exposure to some infectious agents is protective against immune-related disorders isn’t new and comes with significant scientific heft. The so-called hygiene hypothesis is constructed from epidemiologic evidence, laboratory studies and clinical trials that, put together, support the notion that an excessive emphasis on antisepsis is implicated in misalignments of the immune system that risk disease.
Allergic and autoimmune diseases are far less common in communities with less hygiene, and autoimmune disorders increase in children who migrate from areas with less emphasis on hygiene to areas with more emphasis. They are less common in agricultural communities, where exposure to dirt and animals is common, compared with neighboring communities with shared genetics but little farming. Children who attend daycare early in life—runny noses, colds and all—have less asthma and fewer allergies. Animal studies, laboratory experiments and small trials in humans all point in a similar direction: Avoiding exposure to some microbes prevents the immune system from training well and predisposes to autoimmune diseases.
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This isn’t a paean to infections and poor hygiene but a reminder of the importance of balance. When I prescribe antibiotics, they have to be strong enough to treat my patient’s infection. But if I overtreat, I run the risk of giving the patient colitis (inflammation of the colon) without additional benefits. Current hygiene policies and practices need rebalancing.
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The extreme concern for hygiene at the onset of Covid-19 was intuitive and understandable. The virus was spreading fast, information on routes of transmission was limited, and we as a society tried to protect one another from infection. But policies that were easy to support two years ago need re-evaluation. Distancing, deep-cleaning and masking aren’t “more is better” kinds of goods.
On the other side of the balance, health risks from extended intensive hygiene are credible. As Omicron recedes and we internalize the paucity of Covid-19 benefits from some hygiene practices, we should balance those against the benefits we lose by shielding our immune systems from normal exposures—and the ones we withhold from children by preventing the exchange of microbes through play and smiles.
For the full commentary, see:
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(Note: the online version of the commentary has the date February 1, 2022, and has the same title as the print version.)