I'm not actually sure, I only bathed them a couple times when they'd gotten particularly stinky, but they mostly just keep themselves clean through grooming. I think you just gotta be careful to avoid harsh soaps and make sure to dry them thoroughly after so they don't get cold.
Highly recommend them as pets! Only reason I never got more after my girls died was because of allergies, but they're a lot of fun to keep. They need to be at least in pairs since they're social animals, and they need large cages and regular free roam time. But aside from that they're pretty low maintenance. Only downside is the short lifespan.