When you go to the gym, do you wash your hands before and after using the equipment? Bring your own regularly cleaned mat for floor exercises? Shower with antibacterial soap and put on clean clothes immediately after your workout? Use only your own towels, razors, bar soap, water bottles?

If you answered “no” to any of the above, you could wind up with one of the many skin infections that can spread like wildfire in athletic settings. In June, the National Athletic Trainers’ Association, known as N.A.T.A., issued a position paper on the causes, prevention and treatment of skin diseases in athletes that could just as well apply to anyone who works out in a communal setting, be it a school, commercial gym or Y.

The authors pointed out that “skin infections in athletes are extremely common” and account for more than half the outbreaks of infectious diseases that occur among participants in competitive sports. And if you think skin problems are minor, consider what happened to Kyle Frey, a 21-year-old junior and competitive wrestler at Drexel University in Philadelphia.

Mr. Frey noticed a pimple on his arm last winter but thought little of it. He competed in a match on a Saturday, but by the next morning the pimple had grown to the size of his biceps and had become very painful.