When deciding to wear an undershirt or not, or deciding what kind to wear, your goal should always be invisibility. Whether it's poking out of your open shirt collar, or the clearly visible t-shirt sleeves beneath your dress shirt, neither of these are good looks for a man.
Carson Kressley, of 'Queer Eye for the Straight Guy' fame, has been known to enforce a very strict No Undershirt policy when he dresses people. I happen to agree with him. Unfortunately, most of us know that is not always practical due to climate and/or biology.
Picking the right dress shirt
When choosing a dress shirt to wear, an important consideration is whether you plan to wear an undershirt beneath it. Some cotton dress shirts are woven more thinly than others, and the thinner the shirt, the more visible your undershirt will likely be. Hence if you want to wear a thin dress shirt, it should be on a day you don't feel the need to wear an undershirt... be it due to humidity, warmth or otherwise.
Picking the right undershirt
This should be obvious, but when picking the right undershirt color should be your first consideration. White is the often the obvious choice, but having heather gray and black options around is also wise. When picking the color, you want the one that will blend in the most and be least visible.
Women often wear thongs to prevent having visible underwear seams showing. You can think of your undershirts similarly. Often cheap undershirts, like the ones found in multi-packs from places like target, will be a thicker cotton and have even thicker neck and arm seams. These elements will likely make such shirts quite visible under clothing. The better choice is to spend a few more bucks and get more carefully made t-shirts that are thinner and have subtler seams.
The next choice is crew neck or v-neck. This is a pretty easy one. If you are wearing a shirt and tie, with the shirt buttoned up all the way, go with crew neck. If you plan to leave a button or two undone, go with v-neck. If possible you should go a step further and find v-neck that are deep enough to not be visible when your shirt is undone.
Lastly is fit. Your undershirt should fit comfortably but snugly. It will add less bulk that way, and make it less visible.
Bonus of wearing an undershirt
I can't believe I'm saying this, but there is one notable potential benefit of wearing an undershirt. Off the heels of the massive success of Spanx shapewear among women, there are now some interesting options for men as well
. Both Spanx
, and a company called Ript Fusion
, make shaping undershirts for men. These shirts are cotton up top around the chest and arms, but use a tighter stretch material around the mid-section. Yes, they can be a little tough to get on depending on your size, but once on they do provide a quite noticeable slimming effect and can actually make your clothes fit better, pants included!
Concluding the undershirt debate
When it comes down to it, if you can avoid wearing undershirts I would advise doing so. Unless you feel like you're going to sweat through your nice dress shirt, there is really no pressing need for undershirts. If sweat if your only problem, antiperspirant like "drysol" is something you might want to look into. Believe if or not, you can even get botox in your underarm area, which will stop most people for sweating for months.
All that aside, if you still feel compelled to wear undershirts, use the information I've outlined to pick the right one and hopefully nobody will ever know it's there, and it might even make you look slimmer.