Underwear are clothes worn under other clothes, often next to the skin. They keep outer clothes from being made dirty by sweat. They also shape the body and provide support for parts of it, and in cold weather help the wearer to keep warm. Underwear can be used to protect the wearer's modesty, as well as to make them look sexy. Special types of underwear have religious importance. Some items of clothing are made to be worn as underwear, while others such as T-shirts and certain types of shorts can be used both as underwear and as outer clothing. If made of suitable fabric, some types of underwear can serve as nightwear or swimsuits.
Items of underwear commonly worn by women today include brassieres (bras) and panties (also known as knickers), while men wear briefs, boxer shorts or boxer briefs. Items worn by both women and men include T-shirts, sleeveless shirts, bikini underwear, thongs and G-strings. In countries where the weather is cold, long underwear can be worn to keep warm.