Why does the commander wear a mask in the command center? Whenever the commander is in the battle room, her face is always covered by a white mask. 



I thought it might be some unexplained atmosphere thing, but when Yuhata is in the command center, she is perfectly fine without one.



And it's not covering up a hideous wound, because we've seen her face before:



Maybe this was explained before and I missed it, but why does she wear this during battle?
It's been a while since this was asked and is pretty much covered in the comments, but here's an answer.

Captain Kobayashi is part of the immortal council and therefore doesn't age. If she walked around never aging people would notice, hence the mask. It probably also serves as a way to hide emotion from the crew, show strength and all that.

Sidonia's wikia page is pretty barren, but there is some stuff there.