Jock itch is caused by a fungus, called tinea, that thrives in damp, dirty environments. Your best defense is to shower or bathe regularly, making sure to dry yourself off completely. Wearing loose-fitting clothing also can help, so that moisture doesn't build up between your clothing and your skin.
Tinea, sometimes known as ringworm (though it isn't a worm), is the same fungus that causes athlete's foot. Athlete’s foot is commonly accompanied by jock itch and fungal infection of the nails. Any step you take to avoid athlete's foot, such as wearing sandals in public bathing areas, where the fungus may have been left behind by someone else, also can help prevent jock itch.