My dog’s black mouth is losing color and looks red

A previously black mouth now fading, from the picture, may be hair loss exposing red lip skin, considered from pathogenic infection like fungal, mite, bacterial, or allergy.

If a clinic is inconvenient, give pet broad-spectrum anti-inflammatory, anti-allergy oral medicine plus a mouth antibacterial spray, and choose low-allergen kibble with lip cleaning after meals. If it improves, continue 2 to 3 weeks; if it spreads, see a vet. Use a collar during treatment.