Risk Level: Low.
Skin provides a strong defense against invading germs. “Unless you abrade, pierce, or scratch it, the skin rejects infection effectively,” says William Schaffner, a professor of preventive medicine at the Vanderbilt University Medical Center, in Nashville. But some infections, like staph, are becoming more prevalent, particularly at gyms.

Watch Out For…

Makeup: “In general, sharing blush or foundation is not a good idea,” says Nelson Lee Novick, a clinical professor of dermatology at the Mount Sinai School of Medicine, in New York City. “Bacteria on your skin may not cause you problems, but it can infect others.”

Shoes and Socks: One of the most common risks is athlete’s foot. If you borrow shoes, wear your own socks, and if you borrow socks, make sure they’re clean.

Toilet Seats: Touching a toilet seat with your hands is riskier than sitting on it. If your dirty hands then touch your mouth, germs can enter your system. But don’t stop covering public toilet seats with paper (if the seat is germy, you could end up with an infection). And — OK, it’s obvious — wash your hands afterward.

The Gym: The biggest risk comes from sharing towels. Dirty towels, as well as gym floors, can spread staph infections. This can happen at home, too, which is one argument in favor of monogrammed towels.