You were not meant to be alone: The human body contains and is covered in an almost unimaginably large number of microbes. But eradicating them as we do, intentionally and unintentionally, with the prolific use of antibiotics may be harming our health, according to one scientist who studies our minuscule companions.

“Overuse of antibiotics could be fueling the dramatic increase in conditions such as obesity, type 1 diabetes, inflammatory bowel disease, allergies and asthma, which have more than doubled in many populations,” writes Martin Blaser, a professor of microbiology and chairman of the department of medicine at New York University Langone Medical Center.

Humans are sometimes called meta-organisms, because of the sheer number and volume of microbes that share our bodies — living in our guts, on our skin, even in our belly buttons. Evidence is building for the benefits these healthy microbial communities offer us. They help us access nutrients, such as vitamin K, and energy from complex carbohydrates. They deter dangerous infections, and recent evidence indicates they help keep at bay multiple sclerosis and other autoimmune disorders.