The Hygiene Hypothesis

There’s a reason why your mother wanted you to go outside and play, aside from getting you out of her way. Playing outside is good for a child’s immuno-development. The Hygiene hypothesis says that childhood exposure to germs and certain infections helps the immune system develop. Conversely, non-exposure can lead to a less robust immunity. This theory is being used to explain the high incidence of autoimmune diseases in children in western countries (asthma, allergies, or eczema). (1)

In the U.S. there is plenty of evidence to support the Hygiene Hypothesis. According to the Centers for Disease Control and Prevention (CDC), asthma is the leading chronic disease in children. Currently, there are about 6.2 million children under the age of 18 with asthma. In 2013, about 13.8 million missed school days were reported due to asthma. (2) The prevalence of childhood eczema in the US is around 10% and about 8% have food allergies. When we start to add in socioeconomic background, it is no surprise that lower-income children were more affected by each of these issues. (3)

In 2020, a group of scientists in Finland decided to explore the possibility of reversing the Hygiene Hypothesis. Over twenty-eight days, children at ten different daycare centers were given the opportunity to play for ninety minutes in yards that were “enriched with microbial biodiversity” which included adding turf from natural forest floors, shrubs, berries, and mosses. The results showed a change in both the skin and gut microbiota of the children. (3)

Of course, there should be a bit of caution in considering the Hygiene Hypothesis. While it is definitely a good idea for children to play outdoors and get exposed to good bacteria, there are limits to how and where this applies. Children should still be encouraged to wash up when they come in from playing outside, or after playing with the family pet.

Hand washing is still important, before a meal, after using the bathroom, after a sneeze or cough. So is cleaning food preparation surfaces before and after use. (5)

Targeted Hygiene

So it becomes a bit of a balancing act. Allowing children to be exposed to some bacteria on a regular basis can help build immunity. At the same time, they should be taught proper, healthy habits when considering personal hygiene. Targeted hygiene suggests that we focus on the places and times that hygiene matters. It subscribes to the idea that it is possible to inhibit infections while at the same time exposing children to the ‘good bacteria’ required for a healthy microbiome.

Sally Bloomfield, an honorary professor at the London School of Hygiene suggests that children, and their parents, should be taught about how infections occur and the concept of targeted hygiene. “This should embed best practice of hygiene from an early age and promote a consistent understanding of the terminology used to talk about hygiene and hygiene issues.” Bloomfield also wants the media to be more educated so that they are not offering confusing or counter-productive messages. (5)