I’m a first time rat owner and my girls have been healthy and happy for the past year! Recently I noticed a thinning patch of hair on one of my girls face. There are no other missing patches of fur and none on my other girl either, as well as no scabs, bleeding, or noticeable bugs. Could this just be over grooming? Old age? Or maybe even her sister grooming her too much? Im seriously doubting it’s mites because there seems to be no other factors, though I’m still worried! Any ideas?