This story was originally published on Oct. 17, 2019 in NYT Parenting.

Our bodies house an extraordinarily vast collection of bacteria and other microorganisms — so many, in fact, that scientists now estimate there may be just as many bacteria in our bodies as human cells.

They thrive on the skin, where they might help protect it from infection, and in areas like the intestinal tract, where they help break down food and absorb nutrients. Given the sheer volume, it’s no wonder scientists are discovering that these microbes play an important role in health and disease.

Research on the microbiome, that collection of microorganisms, is still in early stages, but it has become increasingly common to hear references to the microbiome in the news and advertising. Last week, Bill Gates wrote an essay for The Telegraph suggesting that correcting an “out of whack” microbiome — by taking next-generation probiotic supplements, for example, or eating certain gut-healthy foods — could eventually help prevent some of the world’s most common ills, such as malnutrition, obesity and perhaps even inflammatory conditions including asthma, allergies and some autoimmune disorders.

And Dove has been advertising an infant soap with “prebiotic moisture,” as well as a lotion claiming that it “nourishes baby’s delicate microbiome.” Mother Dirt, a skin-care company, also has said that its “biome-friendly” cleansers, shampoos, moisturizers and more help “restore harmony in your skin’s microbiome.”