It's not good for them to breathe the urine fumes, and they can also get a nasty foot problem known as bumblefoot from standing in the wetness. (hypeorlando.com)
Having their feet constantly pressed against wire can cause a painful condition called bumblefoot, where your guinea pig's feet may swell and become infected. (northstarrescue.org)
A hamster's foot can get stuck in the wheel and cause bumblefoot. (wikihow.com)