Q. Red stain around mouth
A. This could be from eating something red in color, bleeding in the mouth or, a darker red can be normal saliva staining. I recommend getting him seen by your vet to check his mouth and make sure he isn't having dental problems.
DR. CHRISTIE LONG, D.V.M., C.V.A.
A. Sometimes dogs will get red staining around their mouths when they have something called lip fold dermatitis. It often accompanies allergic disease, and can be caused by food allergies or environmental allergies or both. There's likely a secondary bacterial component that's causing an infection in this area. A vet who's competent at treating skin disease (especially allergic skin disease) would be able to help you with appropriate therapies.