Children's Immunity: Microbes vs Antibiotics

Microbes, Not Antibiotics, Build Strong Immunity in Children

Canadian researchers have reached a compelling conclusion: children need exposure to microbes—not antibiotics—to develop robust immunity. According to the science, letting children play in dirt and mud is actually good for them. It helps their immune systems mature and reduces the risk of chronic diseases like asthma.

Yes, hand washing matters. It's critical during cold and flu season, especially before visiting hospitals. But here's the problem: at least in the Western world, parents have taken cleanliness too far.

"New research confirms that destroying microbes with hand sanitisers, antibacterial soaps, and overprescribed antibiotics damages our children's immune systems," says Marie-Claire Arrieta, microbiologist and co-author of Let Them Eat Dirt: Saving Our Children from an Oversanitized World.

Brett Finlay, an associate professor at the University of Calgary and respected microbiologist, agrees. Together they argue that today's children grow up in sterile environments. Yet excessive cleanliness paves the way for chronic disease—from allergies to obesity. Below is a summary of Arrieta's thinking from an interview in the Toronto Star.

What Inspired You to Write This Book?

As microbiologists, we study microbes living in the digestive tract—what's called the gut microbiome. In recent years, our lab and others have shown that the health of this microbiome in a child's early years determines their long-term health. Since we're both parents, we felt our scientific findings could help other parents and caregivers understand what we've discovered.

The Real Impact of Antibiotics on Developing Immunity

We've long known that antibiotic overuse can create resistant infections in hospitals, something we see in elderly and immunocompromised patients. But I think the impact is much more direct and personal than that. What's the connection between microbes and the developing immune system in children?

At birth, a child's body contains no microbes. The immune system isn't fully formed. But the moment microbes arrive, they switch on the immune system and train it to work properly. Without microbes, the immune system can't fight infection.

It's not just about the microbes themselves—it's what they produce: molecules and substances that talk directly to cells in the gut wall and also to immune cells on the other side of that wall. They literally train them. Only through exposure to these microbes does an immune cell learn what it's supposed to do. Cells in the gut can then travel to other parts of the body to continue learning.

Growing Up in a Microbial World

When we grew up, things were different. We played outside, we got dirty, we ate without washing our hands first. We were exposed to far more microbes. That constant low-level challenge kept our immune systems active and educated. Today's children live in homes that are too clean, attend schools with hand sanitisers on every corner, and receive antibiotics for minor infections that would have resolved on their own.

The science is clear: immunity isn't built in a bottle of antiseptic. It's built through experience—through exposure, through challenge, through the daily contact with the microbial world that shaped human health for millennia.

So yes, wash your hands before eating. Practise good hygiene during illness. But let your child play in the dirt. It's doing more for their health than any sanitiser ever will.