The term microbiome refers to the landscape of bacteria inside our bodies—it plays an integral role in the health of the gut, which in turn affects nearly every other system, including the largest organ, your skin. But widespread (and increased) antibiotic use is killing off our good microbe populations. According to the Centers for Disease Control and Prevention, 266.1 million courses of antibiotics were prescribed in 2014—and researchers say at least 30 percent of those prescriptions were unnecessary. This reckless pill popping is bad news for the skin: Studies suggest that changes in skin bacteria play a significant role in conditions such as atopic dermatitis and psoriasis.

Antibiotics aren't the only offender throwing off our microbiome. "Certain common ingredients in personal care products, like the zinc pyrithione found in dandruff shampoos, and some alcohols found in products like toners, can also kill off good bacteria," says Matthew Zirwas, M.D., director of the Ohio Contact Dermatitis Center, who says he has seen an increase in irritating skin issues related to yeast overgrowth, which can result from a dearth of good microbes.

Swapping out processed foods and sugar for a fiber-rich diet with lots of fermented fare (like kimchi and kombucha tea) will go a long way toward getting your gut and skin in a happier place. Furthermore, "I have most of my patients take a probiotic, a supplement that supports the growth of healthy bacteria in our bodies. My basic rule of thumb is: the more strains of bacteria, the better," says Zirwas, who recommends Now Probiotic-10 100 Billion ($21 for 30 capsules, amazon.com).