Since April my 13 year old cairn terrier's nose gets crusty on the sides, heals up, then is raw for a day, gets crusty, & heals. I do not know why, but his nose has not been "regular". It does coincide when I changed to a senior kibble. He was eating the regular Blue Buffalo kibble, but getting chunky. I got the senior Blue Buffalo in April. I stopped feeding him the senior food last week and went back to the adult food again in hopes that is all it was. He has his annual exam next week so I hope I find out.