Ah, the ancient question. I was pretty confused about this for a while at some point. The thing is, there is no contextual evidence to Snape having any facial hair, but there isn't any evidence to him not having facial hair either.
One of the main things about this is that the illustrator for the American copies of the books always draws Snape with a goatee and mustache. I really don't like the way he's drawn, though... He looks like this in the chapter illustrations:
Everyt time I get to this chapter, I just groan inwardly and I'm all, "Ugh, why'd they have to draw him so ugly? This doesn't even make any sense--why would he even look like that? And why the hell is he sticking out his pinky like that?"
I suppose people might assume that Snape has a goatee because it makes him look more evil. But then again, if he had an evil goatee, wouldn't he be twisting it around his finger all the time to emphasize how evil he is? You know... like Jafar from Alladin? Now that I think about it, Snape needs a talking parrot for a pet. Or a talking bat.
But seriously, I cannot imagine Snape with any facial hair at all. That would make it harder to kiss him... And I really don't find facial hair attractive unless it's just stubble. Or the various goatees that Alan Rickman has had in his movies. That's probably part of it... Alan Rickman as Snape has no facial hair, and Alan Rickman is Snape, so therefore, Snape is clean-shaven. He probably gets shaved at Sweeny Todd's Barber Shop.
I suppose there are still plenty of people that remain convinced that Snape has some sort of facial hair, but I don't. Let's just agree to disagree.
