Hygiene and Your Immune System

In the age of Covid-19, we wash our hands many times throughout the day and disinfect surfaces constantly. Society as a whole has probably become more sanitary in the past four months. And yet, there’s evidence that in the pre-Covid era, we were already little too clean for good immune health. Hygiene has turned out to be the most controversial of the eight immune system fundamentals. Let’s look at hygiene and how it affects your immune system.

Hygiene and Your Immune System

Harvard Medical School offers the traditional view of hygiene. It advises us to stop infection before it begins and avoid spreading it to others with four hygienic habits. These habits are washing your hands frequently with soap and water, covering your nose and mouth when you cough or sneeze, washing and bandaging cuts, and avoiding picking at healing wounds.

This is all good advice, and its simple rules can help take some pressure off your immune system so it doesn’t get overworked. But it looks increasingly that our immune systems, far from being overworked, may be losing fitness as a result of under-use. This idea vaulted to prominence in a 1989 article (PDF) by David P. Strachan detailing his study of 17,414 British children. Strachan tabulated the instances of hay fever, allergic rhinitis, and eczema among children born in 1958. Among 16 factors, the two best predictors for those conditions were (inversely) family size and birth order.

Immune System “Fitness”

Strachan found the children with the healthiest immune systems were those with the most older brothers and sisters. Older brothers and sisters meant indirect contact with other children outside the home, as well as various environmental influences. Presumably, the constant challenges to their immune systems gave such children the healthiest immunities. This has since acquired the name the Hygiene Hypothesis. In 2006, researchers summed it up: “a cause of the recent rapid rise in atopic disorders could be a lower incidence of infection in early childhood, transmitted by unhygienic contact with older siblings.” 

A CDC Data Brief from 2013 (PDF) noted that among children under 18, in the first 10 years of the 21st century, food allergies and skin allergies increased dramatically. Food allergies went from 3.4% to 5.1% of children, and skin allergies went from 7.4% to 12.5%.

The increasing hygiene in our lives is seems to contribute to increasing allergic and autoimmune conditions. Much of the evidence for this was detailed in the 2019 book, An Elegant Defense: The Extraordinary New Science of the Immune System, excerpted in the New York Times.

The Covid-19 Era

So a significant proportion of modern health problems arise from excessive hygiene. Our over-use of antimicrobial cleaning products and the over-prescription of antibiotics are subtly undermining our health. These ultra-hygienic practices have three unhealthy results:

    • reduce pressure on our immune systems
    • destroy beneficial bacteria in our guts and on our skin
    • stimulate the evolution of antibiotic-resistant bacteria.

And yet, survival in the age of Covid-19 requires that we frequently disinfect surfaces, wear a mask over our nose and mouth when interacting with others, and frequently wash our hands. Cultivate these habits. Your health and your immune system depend on it. Just don’t use antibacterial soap. And don’t ask your doctor to prescribe antibiotics for a cold. And, if life ever gets back to normal, consider giving your immune system the benefit of being just a little bit less antiseptic in your daily living.

Photo: “clean hands” by Arlington County is licensed under CC BY-SA 2.0