Your skin is host to colonies of trillions of microbes such as bacteria, fungi and viruses that are not harmful, and understanding them better could lead to cures for conditions such as eczema and acne.

“Understanding these microbes and how we might be able to change them, and how they’ve been changed by our habits and our environments, holds a lot of promise for people who are suffering from those conditions,” said James Hamblin, author of “Clean: The New Science of Skin.”

Hamblin is a preventative medicine physician and a staff writer for The Atlantic, and also author of “If Our Bodies Could Talk.”

“It wasn’t until about 10 years ago that we started to have the technology to understand the breadth and number of just how many of these things there are. We’re talking about trillions,” Hamblin said.

The microbiome on everyone’s skin is unique to each individual. “You and I share 99.9% of our DNA, but we probably only share about 60% of our microbiome,” Hamblin said.

And that might explain why some skin care products that work for a friend might not work on you.

“Some things work for some people, and other people, it made them break out, and for others, it was a miracle, and for a long time we didn’t understand that,” Hamblin said. “We thought, ‘This person must have misused the product, because for me, it was great.'”

Your skin’s microbiome feeds on oils on your skin, and nearly everything you do disrupts the habitat in some way.

“There are clearly correlations between people who do are doing a lot of aggressive washing, and people who end up having to treat that with emollient creams and moisturizers,” Hamblin said.

“It’s clearly possible, just like anything now, to take a practice that on your hands is absolutely vital — it’s lifesaving intervention to wash your hands — but you can absolutely overdo it on the rest of your body,” he added.