Why Cats Develop Black Crusts (Scabs): Causes and Treatment

Black crusts on a cat, such as around the nose, are dried mixtures of serum, blood, pus, and scale. They can stem from primary problems like idiopathic seborrhea, but more often signal an underlying skin disease such as ringworm, insect bites, or pemphigus foliaceus, so a veterinary diagnosis is needed before treatment.