Risk Level: Low.
Hair is made up mostly of nonliving protein, and infections usually require living material to spread, says William Schaffner, a professor of preventive medicine at the Vanderbilt University Medical Center, in Nashville. But parasitic infestations of the head, such as lice, can be very contagious, giving new meaning to the phrase “bad-hair day.”

Watch Out For…

Hairbrushes, Combs, Hat: While it’s best to use your own, sharing these things is probably fine as long as there’s not a lice epidemic in your town. There’s a slight chance of contracting a fungal infection — such as dermatophytosis, which can live in the roots of the hair — from an infected brush or comb, says Nelson Lee Novick, a clinical professor of dermatology at the Mount Sinai School of Medicine, in New York City.

Headphones, Pillowcases, Blankets: Again, absent a lice epidemic, sharing these things is probably OK. But avoid using them on airplanes — even if you haven’t already seen the in-flight movie.