Hello, I have a black and white cat who is about 10 years old. He lived the first few years of his life in the alley but since I adopted him in 2001 he's been an indoor cat. About 6 months ago he developed a funny little black spot on his nose. The spot stays around for 3-4 weeks and then it falls off. When it does, the skin underneath is slightly red. Then the spot returns. I'm not sure if it's a scab or what, but it worries me a bit. I've attached a picture. Should I be worried?