An undershirt may look like a T-shirt but they're going to be thinner and more breathable than regular T-shirts. You can find them in V-neck or crew neck shirts. If you're planning to wear a fully buttoned dress shirt or a sweater then crew necks are your best choice.

What is considered an undershirt?

An undershirt in American English (vest in British and Indian English, or singlet in Australia and New Zealand), is an article of underwear worn underneath a dress shirt (or sometimes T-shirt) intended to protect it from body sweat and odors. It can have short sleeves (T-shirt) or be sleeveless (A-shirt).

How do you tell if a shirt is an undershirt?

Undershirts have shorter sleeves, so they can be worn under short-sleeve shirts, such as polo shirts, as well as long sleeve shirts. T-shirts have a shallower v-neck. While deep v-neck t-shirts do exist, they are not widely worn. Undershirts have deeper v-necks.