cleaning stains on white muzzles

Question
Hi.  I have a 7 year old Westie whose muzzle is very stained. It wasn't that way the first couple of years. I don't know how to correct it or prevent it. Is it from her own saliva or just food? Can it be cleaned or does it just have to grow out? That's assuming I can prevent future staining. Any advise would be much appreciated.  Thanks.

Answer
It will be almost impossible to prevent. Nothing cleans it out either. Showdog people struggle with this same thing. It is from saliva and just getting wet. Sometimes you will find their feet will turn somewhat rusty too. Just something you have to live with when you have a white dog.