Undershirts are a staple for the well-dressed man. Undershirts give dress shirts a smoother line and allow shirts that may have thinner material a better look. For a tuxedo shirt, wearing an undershirt is important because it will give the wearer a layer between the formal wear and any perspiration. During a hot June wedding with a nervous group, this is very important. A cotton undershirt will keep sweat and stains safely away from the shirt.

On the Other: Some men don't want the extra burden

Some men have gone away from wearing an undershirt with a tuxedo because another layer only adds to the uncomfortable nature of wearing formal wear. Also, many tuxedo shirts will have a double layer of fabric, especially on the shirt front, that will give a smooth line and look and protect against any sweat stains. If a wearer wants one less piece of clothing to worry about in a formal ensemble, he is not going to want to choose an undershirt.

Bottom Line

Tradition should dictate when it comes to formal fashion, so wearing an undershirt is the best way to go on this. There is too much risk when deciding to go without wearing an undershirt under a tuxedo shirt, ranging from others being able to see your chest through too-thin fabric to stains caused by perspiration.

Source:

AskAndy.com: Forum debating undershirts under tuxedos

Fibers.com: Should undershirts be worn under tuxedos?