The next time you find your child playing in the dirt, you might want to think again before stopping them if you want them to have a strong immune system.

Numerous studies indicate that playing in the dirt during childhood may play a crucial role in strengthening children’s immune system, lowering their likelihood of developing allergies or autoimmune conditions, according to Live Science.

This means that it may guard against conditions in which the immune system unhelpfully reacts to allergens or to the body’s tissues.

This phenomenon occurs as a child’s immune system matures during the early years, helping the body’s protective cells learn to differentiate between harmless substances, like dirt, and harmful pathogens such as bacteria and viruses.

This natural process not only helps in identifying and combating actual threats but may also prevent the immune system from overreacting to benign allergens.

It turns out that the molecular signals that drive the expansion of this regulatory arm of the immune system mainly come from microbes in the gut, Graham Rook, a professor emeritus of medical microbiology at University College London, told Live Science. 

This collection of microbes is called the “gut microbiome” and is essential to human health. For instance, some of these microbes help produce vitamins that humans need to live, and help them digest their food.

The first year of a baby’s life is critical for developing the microbiome, as they acquire bacteria from the birth canal during delivery and from breast milk if breastfed.

As children grow, they encounter a variety of microbes from different sources.

A theory called the “old-friends hypothesis” suggests that the greater the range of microbes kids are exposed to in early childhood, the more diverse their microbiomes will be and thus the better their immune systems will recognise friend from foe. 

The term “old friends” refers to helpful, or “commensal,” microbes that live on and in the body without harming a person’s health.

A trial in Finland looked at whether city kids’ immune systems could be bolstered with grass and soil that had been taken from the forest floor. 

They found that, within a month, children who played in the dirt had a more diverse collection of harmless bacteria on their skin and more immune-regulatory cells and signaling molecules in their blood than those who played on gravel playgrounds. 

Encouraging children to play with dirt can benefit their immune systems, according to experts. However, translating current scientific understanding of immune condition risk factors into practical advice is challenging.

For instance, if you have a dog, you may have a somewhat lower chance of developing allergies than a pet-less person — but one can’t tell somebody to get a dog as a guaranteed way to prevent allergies, said Dr Robert Wood, a professor of pediatrics at Johns Hopkins Medicine in Baltimore.

Dirt in heavily polluted areas can also be unhealthy for kids, as it could contain harmful contaminants, he noted. This clearly wouldn’t be the sort of dirt that you’d want your child to be exposed to. And because dirt can contain potentially harmful chemicals, such as lead, as well as parasites, care should be taken to stop children from inhaling or eating it.