[MotoSook]

A dress shirt that's been starched and pressed should always have an undershirt. If you don't like the collar of the undershirt showing behind an unbuttoned dress shirt, buy v neck tees. The tees should be a simple white undershirt. Without the undershirt, you'll look cheap and unfamiliar with wearing a dress shirt. The undershirt also makes wearing a starched dress shirt more comfortable in any climate. The undershirt can also give your dress shirt a second wearing if you don't dirty it on the first wearing. If you wear dress shirts to the office, this will save you some money at the dry cleaners.

In the winter I even wear a long sleeve undershirt.

If your dress shirt is thin you definitely want an undershirt as some have stated the reasons why.

If you're wearing jeans and a dress shirt, an undershirt is optional. It depends on the dress shirt. A more formal dress shirt, should have an undershirt.

I can always spot a guy who doesn't often dress up or follow good dress form. When he does dress up, he'll have a dress shirt and slacks with no undershirt.

Believe me, most ladies notice the undershirt. If you don't have an undershirt and you're supposed to be dressed up, you'll lose points. When out at a club a dress shirt (in the right print or color) sans an undershirt worn with nice jeans and nice shoes, top button undone makes the right statement.

A polo shirt isn't a dress shirt so you can go without an undershirt, but in cold climates an undershirt is perfectly fine.