A rash guard is a close fitting, stretchy top, usually made from a blend of polyester and elastane, worn under a BJJ gi or on its own during no gi grappling. Its main purpose is to reduce friction between skin and fabric, or skin and mat, which lowers the risk of mat burns and general skin irritation during rolling.
Because grappling involves sustained contact and grip exchanges, a rash guard also helps manage sweat and keeps a gi's inner lining cleaner over time, which supports basic hygiene in a shared training space. For no gi classes, a rash guard is often paired with spats to form a complete, snug fitting kit that leaves an opponent little loose fabric to grip.
Fit should be snug without restricting shoulder movement, since a loose rash guard bunches up during grip fighting and defeats much of its purpose. Many competitions under grappling rulesets specify what a rash guard must look like, including limits on graphics or logos, so checking event rules before a tournament is worthwhile. See our uniforms and belts overview for related equipment.
