i have recently noticed that my mouse is going bald just to the bottom right of her left ear there is a large patch of skin witrh no fur

is she ill

i have had her for a few months
she is not very old

my other mouse that i keep her with is fine

i have not changed their diet recently

here is a pic

http://i124.photobucket.com/albums/p29/punkypunkyfish/baldmouse.jpg
the picture is really blurry because she runs very fast sorry

i did circle the area but that was the best i could do