I've heard that too, but it's not entirely true. It is true that acne comes from bacteria in the skin, and it can cause pore blocking in areas, but for the most part, semen is quite sterile (unless of course carrying an STD). Much in the same way that urine is sterile when it leaves the body. That's why you can hear stories of people being able to stay alive in extreme cases where they have to drink their urine. Though it should be boiled first if you have to do it.
Also, a guy who can make semen get all the way up to his face is pretty impressive, i must say. It's rare that it would shoot all the way up there, unless of course he's hunched over waiting for it.
H-D 