The puffy, mustache shaped skin resembling a bald mustache on some guys upper lip.
"Hey Dude, did you shave your mustache?"
"No, I just covered it with concealer."
"Yeah, Wow, I really didn't notice."
This is what occurs when a woman has been tanning in the sun or with sunless tanner, and has her upper-lip waxed. Waxing removes the top 3 layers of skin, therefore removing the tan and leaving a white "skinstache".
"Oh dear, I shouldn't have gone tanning and then have the salon wax my mustache! Now I have a skinstache."