Acanthosis nigricans can occur due to -
Hyperplasia of stratum spinosum of the epidermis.
Hyperkeratosis → Thickening of Stratum corneum of epidermis (Cornification of epidermis).
Slight basal cell hyperpigmentation.
Increased multiplication of basal cells
Cornification of basal cells
Keratinisation of epidermal cells
All
Keratinisation of epidermal cells