Fabric traps in moisture, so wearing underwear can make you perspire even more. “Sweat absorbs the heat from your body and releases it when it evaporates,” says Philip Deer, education manager at the Equinox Fitness Training Institute in Beverly Hills. The double layer can cause overheating (which increases your rate of perceived exertion) and up your chance of getting a yeast infection.
Going commando minimizes those risks. It also makes chafing less likely, adds Joshua Zeichner, MD, the director of cosmetic and clinical research in dermatology at Mount Sinai Hospital in New York City. Thongs often irritate the perineum and boxers bunch up and rub against the skin, which can lead to jock itch.
The bottom line:
When you skip underwear during a high-intensity workout, Deer suggests wearing pants or shorts made of sweat-wicking synthetic fabrics like polypropylene, nylon, and polyester, found in most performance gear.
Tights made of cotton-heavy synthetic blends, which are chafe-resistant, are approved for lower-intensity routines that keep sweat at a minimum. Avoid those with a center seam, which can ride up and irritate the skin, adds Jacques Moritz, MD, an OB/GYN at Weill Cornell Medicine in New York City and a member of the Equinox Health Advisory Board.