The best way to let a child develop good gut health is to let them get dirty, allow them to play with pets, wash with soap rather than antibacterial gels, feed them a healthy diet high in fibre, and reduce antibiotic use, according to Professor Brett Finlay, co-author of Let Them Eat Dirt.

“Research shows there is a direct link between lacking diverse microbes in a child’s gut to potential chronic conditions like asthma, allergies, obesity, diabetes and even healthy brain development,” he says.

Microbial scientist Jack Gilbert, co-author of Dirt Is Good, says that sterilising children’s hands with antiseptic wipes as soon as they get dirty or keeping them away from animals are two of the things that parents are getting wrong.

He advocates letting children experience the world so they receive beneficial exposure to microbes which develop gut health.

Mother-of-two Yoki Lau, from Hong Kong, loves to let her one- and five-year-old sons splash in puddles and get involved in messy play.

But she admits she was never allowed to do so herself when she was growing up.

“There was no messy play during my childhood – it was not common. We were not allowed to play in the sand tray in kindergarten. I wasn’t allowed to splash and stomp in puddles as I was told it was dirty and messy.”

Lau, an early years educator, is now an advocate of messy play, believing it helps develop babies’ senses and enhance their development.

“It also helps develop fine motor skills and even helps build nerve connections,” she says. “The first few years of a child’s life are incredibly important for brain growth, and many of the nerve connections are built during this phase. This means the more stimulation a baby’s brain receives, the more connections it will develop.”

In her messy play sessions she encourages children to get covered in slime, paint, shaving foam and even ground coffee.

Her attitude to sanitisation has also changed between having her two sons.

“When my elder child was young, I used to sanitise the dining tables and high chairs when we dined out. I cleaned his hands whenever he touched the handrails or anything. I kept the house really clean and it was honestly so OCD [obsessive-compulsive disorder]. But he still got sick every two months. I am less OCD for my second one and he’s totally fine and even healthier.”

The researchers argue that there is no confirmed evidence of a link between personal or home cleanliness and increased risk of allergic disease. This is because excessive cleanliness does not remove microbes as they are continually being brought into homes via air and dust from the outside, and skin shed from the human body and pets.

In fact, the rise in infectious disease means that hygiene is becoming more, rather than less, important, but there is value in letting children spend more time outdoors in the natural environment to help restore the microbiome, the research says.

All the research seems to suggest that playing in puddles or digging in the dirt is good for gut health as long as a common-sense approach is taken and poisonous contaminants are avoided. There is no evidence that these activities cause ill health, particularly since colds are caused by viruses rather than bacteria.

Project manager Kelly Coskun, also from Hong Kong, believes that letting her three-year-old son Alex “get down and dirty” enables him to develop his creativity.

“I think messy play encourages my son to explore new textures and manipulate different materials through touch, and it is very helpful in enhancing his learning, language and creativity.”

So next time it rains, don’t feel guilty about letting your child jump in muddy puddles – it will do them more good than harm.