Zoe's muzzle used to be smelly when I had it long (her nick name was wet socks because that is what it smelled like lol) but now I keep her muzzle trimmed and I have no more smelly problems. I think it was because she would get her muzzle hair wet all the time when she drank water and that combined with the saliva from licking her chops made her face smelly. Hope this helps!
