Many people wonder whether our society’s desire for cleanliness may have gone too far and is causing health problems. For parents, this raises an interesting question: How dirty should you let your kid get?

Eating dirt might be a stretch, but it’s certainly good for them to play in it, and it’s definitely important and beneficial for children to spend time in natural areas like farms and forests.

Allergists like me are studying whether protecting our body’s barriers and exposing kids to more bacteria in certain contexts could help prevent allergies. The answer to both questions appears to be “yes.”

The scoop on dirt

The revised thinking about dirt comes from something called the hygiene hypothesis. As society progressed from one that was chronically burdened with infectious diseases caused by poor sanitation, we reduced our exposures to the things that gave our immune system an appropriate training and tolerance. For instance, our totally rational fear of dying from a cholera epidemic led to sewage and water management, but may have kicked off the allergy epidemic.

Studies that have looked at kids who grow up on farms have yielded interesting information.

Growing up in a rural area exposed to farm animals appears to confer decreased risk of allergies and asthma for your entire lifetime, even among genetically similar populations. Studies in mice have shown that inhaling certain molecules from soil-dwelling bacteria can set off a beneficial cascade promoting an immune system which focuses more on threats rather than non-threats, such as allergens.

Vaccinations appear to be a crucial exception to the rule of the hygiene hypothesis. They confer protection against diseases without any associated increase in the risk of allergic disease, likely because they, unlike antibiotics, are very specifically targeting only the worst disease-causing organisms.

And, just like everything in medicine, we have to be aware of the competing risks of going too far with the hygiene hypothesis. Children who grow up in areas with poor sanitation or who drink unclean water tend to suffer from higher rates of diarrheal diseases and can be exposed to parasites that stunt their growth. A misapplication of the hygiene hypothesis might also lead people to avoid or delay necessary medical treatments with antibiotics, or to reject beneficial public health interventions that protect our food supply, like pasteurization.

On balance, it’s never wrong to wash your hands when they have visible dirt or after visiting someone who has been sick, but you usually shouldn’t turn your everyday life into the level of sanitized cleanliness expected in a hospital. Similarly, we probably don’t need to choose antimicrobial versions of everyday household products, but having access to antibiotics for a susceptible infection can be life-saving. As a wise pediatrician once remarked during my training, “Babies really only need a bath when they are visibly dirty or they stink, and even then, just use clean water and a little soap in the diaper area.”

Our current prescription

The data currently paints a picture that we might prevent allergies in the future by protecting our barriers and introducing the right tolerizing exposures at the right time, such as early introduction of peanuts.

However, I can’t currently tell you how much dirt or what kinds of bacteria your child needs to safely experience while growing up. It’s too soon for that, but many wonderful scientists around the world are working on these questions, thanks to support from a variety of governments and foundations.

Until then, I will share with you the broad-brush advice that I currently give my friends and patients.

This article is from The Conversation, a nonprofit news source dedicated to spreading ideas from experts. Republished under a Creative Commons license.