My labrador is loosing the hair on the top of her nose, it has been a gradual thinning, not in circles or patches and does not irritate her at all, the skin seems fine underneath.  She is 7 years old and I had originally just put it down to getting older but I'm not sure now.  Has anyone else had this happen to their dogs at all or does anyone have any suggetions as to what it could be if not aging?