Acanthosis involves-
Acanthosis is diffuse epidermal hyperplasia (thickening of the skin). It implies increased thickness of the Malpighian layer (stratum basale and stratum spinosum). Acanthosis nigricans is often associated with type 2 diabetes, and is usually observed in the back of neck, axilla, and other folded regions of the skin. Ref Harrison20th edition pg 1206
Str spinosum
Str granuolosum
Str Basale
Str Corneum
Anatomy of skin