Why Cats Develop Black Crusts (Scabs): Causes and Treatment
📝 Summary
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.
1 What Causes the Crusts
A crust is dried exudate, a mixture of serum, blood, pus, scales, and medication residue. Black crusting on a cat’s nose may reflect a primary cause such as idiopathic seborrhea or metabolic epidermal necrosis.
More commonly it is secondary, appearing in various skin diseases including feline ringworm (dermatophytosis), traumatic dermatitis, mosquito or insect bites, and pemphigus foliaceus. It is best to have a veterinarian confirm the cause before starting treatment.
2 Treating Feline Ringworm
Wash the affected skin with sulfur soap, and bathe the whole body if possible. Restrain the cat and carefully clip the hair around the lesion, taking care not to cut the skin. Use a cotton swab dipped in alcohol to remove scales and hard crusts, then apply terbinafine (or clotrimazole ointment) 2 to 3 times daily.
Spread the medication from the center of the lesion outward to include the apparently healthy surrounding skin, using a circular motion from inside to outside, so the drug penetrates the affected area and prevents further spread. Continue applying for a while after the lesions disappear.
If there is no marked improvement after 2 to 4 weeks of topical treatment, give griseofulvin at 30 mg per kg body weight once daily for 2 weeks; crush the tablet or mix the powder with edible vegetable oil before feeding. Alternatively, give terbinafine hydrochloride at 25 mg per kg body weight.
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