A toddler waiting at the door of a restaurant in Kakaako squeezed his face against the glass, then stuck out his tongue to lick it.

Nearby adults reacted with visceral alarm, but he was just doing what comes naturally. Children in the first years of life have an innate impulse to reach out and touch, taste and feel the world around them.

B. Brett Finlay, one of Canada’s top microbiologists, says new research shows that early exposure to microbes is crucial to the normal development of children and their immune systems. He fears our obsession with cleanliness might be contributing to a new set of problems, from asthma to obesity.

Finlay is trying to get the word out with his new book, “Let Them Eat Dirt: Saving Your Child from an Oversanitized World,” co-authored with Marie-Claire Arrieta. He will explore the issues in a talk at 6 p.m. Tuesday at the University of Hawaii at Manoa.

An expert on bacterial infections, Finlay applauds the revolution in sanitation and antibiotics that has saved countless lives over the past century. He certainly recommends hand washing before eating and after using the restroom. But he thinks we have gone overboard in trying to wipe out microbes, since just a tiny fraction of them cause disease.

“Our zest and our zeal for getting rid of all microbes has actually backfired,” said Finlay, a professor at the University of British Columbia who co-directs the Humans & the Microbiome program of the Canadian Institute for Advanced Research. “We consider every microbe a potential germ, so they’re all fair game to destroy, so we go with the hand sanitizer. We clean everything at all times.”

He added, “What we have done is throw the good bugs out with the bad ones. Microbes play a key role in how our body develops. We know these microbes are essential for the immune system. We know they are essential for how the gut develops and we know they are essential for how the brain develops.”

Finlay uses a couple of graphs to help tell his story. One tracks the incidence of infectious diseases since 1960, including measles, tuberculosis and hepatitis A. That line plunges downward. The other graph shoots upward, showing the explosion in immune disorders such as asthma, Crohn’s disease, multiple sclerosis and Type 1 diabetes. He believes microbial imbalances might have spurred that trend.

The human body is coated inside and out with microbes, mostly bacteria, although they are invisible to the naked eye. Not only humans, but animals, plants, soil, water and ecosystems all depend on a healthy balance of these tiny organisms.

Last year, the federal government launched a National Microbiome Initiative to study these communities of microorganisms and the role they play in human and environmental health. The University of Hawaii is becoming a big player in the field, with three professors specializing in microbiota who are members of the National Academy of Sciences.

One of them, professor Margaret McFall-Ngai, director of the Pacific Biosciences Research Center, is internationally known for her research on the interaction of microbes and their hosts. She invited Finlay to Honolulu because she maintains his book has a message people need to hear.

“I don’t have kids, but I put that book down and said, ‘Oh, my God, every pregnant woman, every parent, every pediatrician, every OB-GYN must read this book,” she said. “It has really important lessons for the future generations.”

She specializes in the role of beneficial bacteria in health and development — and her animal of choice is the Hawaiian bobtail squid, an endearing speckled creature about the size of a thumb.

Shortly after it hatches, the squid attracts a bacterium known as vibrio from the ocean that allows it to glow and camouflage itself as moonlight or starlight on the water. McFall-Ngai and her team are examining how the squid recognizes and harvests the vibrio, how it affects the squid’s development, and how the microbes stay in balance.

Microbes are important from the start, for squids and for humans. Research shows that babies born vaginally pick up their mother’s microbes on the way out of the body and are less likely to develop asthma later in life, Finlay said. So are kids raised on farms, a microbial-rich environment. Breastfeeding also decreases asthma. On the flip side, use of antibiotics in the first year of life increases the likelihood of asthma.

Finlay emphasizes that antibiotics are “a wonder drug” in combating bacterial infections, but he contends they are overused.

Early and repeated courses of antibiotics can “carpet bomb” the microbes that make up a healthy gut, he said. A fiber-poor diet can also affect the microbial balance in lasting ways.

“When you shift to white sugar and white flour, you absorb them very high in your intestine, long before you get to the microbes,” he said. “You are starving the microbes. They need the vegetables, the legumes, fibers, the plant stuff. That’s what the microbes actually break down.”

He cites experiments showing that transferring fecal microbes from one mouse into the gut of another can dramatically alter their physique and intestinal function.

“With a fecal transfer from a fat mouse to a thin mouse, the thin mouse got fat,” he said. “When the transfer was from the thin mouse to a fat mouse, the fat mouse lost weight.”

As for the title of his book, Finlay doesn’t actually recommend eating dirt. But he understands why the little boy licked the door. After all, early exposure to microbes helps train the immune system.

“If it was so bad for us, why didn’t we evolve not to do this?” he asked. “That’s what kids do. They just inhale dirt left, right and center.”