well we get quite a few hints that hange doesn’t really exercise much care over her hygiene; in isayama’s original character notes for the animation team he pointed out that hange’s hair is messy, tangled and greasy/oily from lack of being washed.
and in her character interview and in levi’s character interview they both mention that hange gets so dirty sometimes that levi coordinates these bathing/water attacks on her with her subordinates.
and her room was described (by isayama or in a character interview, I cant recall) as being full of books and dust.
it just kind of fits hange as well; she gets so wrapped in her research and experiments that cleanliness and self-care becomes a much lower priority. so she has moblit and levi to keep that shit from getting too out of hand.