Some people choose not to wear any underwear for several reasons, including for comfort, to enable their outer garments (particularly those which are form-fitting) to look more flattering, to avoid creating a panty line, or because they do not see any need for them. Some people find not wearing underwear to be sexually exciting, and some people regard knowing that their sex partner is not wearing underwear to be erotic. Not wearing underwear is widely considered to be immodest and socially unacceptable if the crotch area becomes exposed, but can be a part of some sex fantasies and of some pornographic films.
Certain types of clothes, such as cycling shorts and kilts, are designed to be worn or are traditionally worn without underwear. This also applies for most clothes worn as swimwear, sportswear or nightwear.
The origins of the phrase "go commando" are uncertain, with some speculating that it may refer to being "out in the open" or "ready for action".
Slate magazine's Daniel Engber dates the modern usage to USA college campuses circa 1974, where it was perhaps associated with soldiers in the Vietnam War, who were reputed to go without underwear to "increase ventilation and reduce moisture." However, more recently, Graeme Donald has pointed out that the US Forces refer to "Rangers" rather than "Commandos", and that in any case, the phrase was in use in the UK, referring mainly to women, from the late 1960s. The connection to the UK and women has been suggested to link to a World War II euphemism for prostitutes working in London's West End, who were termed "Piccadilly Commandos"
The earliest known use of the term in news media occurred on January 22, 1985, when Jim Spencer wrote in the Chicago Tribune, "Furthermore, coloured briefs are 'sleazy' and going without underwear ('going commando,' as they say on campus) is simply gross." 
- Donald, Graeme (2008), Sticklers, Sideburns and Bikinis: The military origins of everyday words and phrases, Osprey Publishing, p. 94, ISBN 9781846033001, retrieved October 19, 2012
- Brennan, John; Taboada, Alvaro. How to Survive the Chilean Jungle (2nd ed.). Santiago, CL: Dolmen Ediciones.
- Gisesa, Nyambega (16 April 2012). "When a little goes a long way to ruin your reputation". Zuqka. Nairobi: Nation Media Group. Retrieved 17 September 2013.
It's during the Vietnamese war, that the earliest cases of going without underwear were recorded. It meant ... being "out in the open" or "ready for action".
- Engber, Daniel (January 10, 2005). "Do Commandos Go Commando?". Slate. Retrieved 2006-12-23.
- Gardiner, Juliet (2005). Wartime: Britain 1939-1945. Headline Review. ISBN 0755310284.
- Wagner, Paul. "Rest and Relaxation, WW II Style". 398th Bomb Group Memorial Association. Retrieved 2014-12-23.
- Barron, Greg Groundrush p. 29 (1982) (1982 novel uses the term - "Bigfoot's jock snapped underneath, leaving him to 'go commando.")
- Heller, Jason; Koski, Genevieve; Murray, Noel; O'Neal, Sean; Pierce, Leonard; Tobias, Scott; VanDerWerff, Todd; Zulkey, Claire (June 21, 2010). "TV in a bottle: 19 great TV episodes largely confined to one location". AV Club. Retrieved June 21, 2010.
[T]he episode also introduced the term 'going commando' into the popular vernacular.
- Hendrickson, Eric (27 October 1996). Buzz word 'going commando' gets an airing on 'Friends', Sunday Times-Sentinel (Gallipolis-Pomeroy, Ohio) (copy from The Detroit News)