In cold climates, underwear may constitute an additional layer of clothing helping to keep the wearer warm.
Underwear may also be used to preserve the wearer's modesty – for instance, some women wear camisoles and slips (petticoats) under clothes that are sheer.
The suitability of underwear as outer clothing is, apart from the indoor or outdoor climate, largely dependent on societal norms, fashion, and the requirements of the law.
Archaeologists have found the remains of such loincloths made of leather dating back 7,000 years.
Not wearing underpants under outer clothing is known in American slang as freeballing for men and as going commando Women's brassieres provide support for the breasts, and men's briefs serve the same function for the male genitalia.
A corset may be worn as a foundation garment to alter a woman's body shape.
Some items of clothing are designed as undergarments, while others, such as T-shirts and certain types of shorts, are appropriate both as undergarments and as outer clothing.
If made of suitable material or textile, some undergarments can serve as nightwear or swimsuits, and some are intended for sexual attraction or visual appeal.