Keratosis or hyperkeratosis is an excessive production of keratin. It can be caused by various factors, most commonly prolonged pressure on a localized area of skin over a hard surface (bone).

The surface of hyperkeratosis may be smooth (callus) or rough and often cracked. Color ranges from white or yellowish to light or dark brown. They may appear in localized forms (e.g., follicular keratoses) or diffuse forms, such as palmoplantar keratoses affecting the entire palm or sole. Diagnosis is based on clinical examination and dermoscopy.

Treatment includes topical salicylic acid preparations (5% or 10% salicylic ointment). If topical therapy is ineffective, electrocauterization is used.