Maybe they all don’t, but since last night I’ve had my TV set to the NASA channel. They keep having these interviews from the shuttle and ISS and this flight engineer - Sunita “Sunny” Williams, every time they show her, her hair is all over. Like medusa.
Is she doing this on purpose? It’s fun? Can’t she just pull it back? Doesn’t all that hair floating around clog up the air filters or something? Are they making her leave her hair undone just to show off the fact she’s in zero G?
Every photo I’ve seen of female astronauts has their hair floating wildly, so I’d say it’s pretty common. Truthfully, I’d have to think that it’d be difficult in microgravity to corral all that hair into a scrunchie or whatever. On Earth, hair’s limited as to where it can go, in space, it’s pretty much unlimited. I’d WAG that it’s a 2 person job getting hair under control, and probably the only time you’re going to want to tie up a second person for such a thing is when “Rapunzel’s” going for a spacewalk.
I also doubt that it’s much of a strain on the air filtration system, since humans are constantly shedding hair and skin (IIRC, 80% of the dust in your house is dead skin cells.).
It probably just feels cool.
Hah. That was funny. 
Maybe the male astronauts think it’s hot.
Now if I were an astronaut, my hair would look exactly the same in space as on earth, because it’s pretty darn short.
Because it’s, like, totally cool