If you’re a runner, you probably already know about the issue of nipple bleeding, but for people like me, who only run when they’re being chased, this is new.

I stumbled across this set of photos on Unknown Highway, one of  my favorite sites, and thought I’d investigate further to find out what exactly makes men’s nipples bleed during marathons. After a bit of reading I learned not to ever run for miles, dressed in a cotton shirt.

Apparently, cotton and sweat just don’t make a good team. After you run a few miles, you start to sweat a lot and the cotton absorbs the sweat and gets heavier and heavier. That’s when it starts to act like sandpaper against your sensitive nipples. So, if you want to run in a marathon make sure you’re wearing something made out of light-weight material, like a CoolMax t-shirt.

If you don’t have anything else but cotton t-shirts, run shirtless. It’s better for people to see your belly wiggling that to see your nipples bleeding, trust me. Also, I know this sounds a bit kinky, but you might want to rub a bit of Vaseline or other lubricant on your nipples, before a race.