Circumscribed acral hypokeratosis (CAH) is also known as circumscribed palmar or plantar hypokeratosis.

It is more frequent in middle-aged or elderly women. It appears as a solitary, acquired, long-standing, asymptomatic lesion involving the thenar and hypothenar regions of the palms or the medial side of the soles (rarely). It is characterized by a circular area of erythematous (the color is due to the more trasparent skin than adjacent thicker normal epidermis), depressed, well-circumscribed, flat-based skin.

Histologically, characteristic features are:

• localized depression of the skin,

• abrupt transition from the normal to depressed horny layer  with a sharp stair,

• thinner, orthokeratotic horny layer in the lesion.

Several hypothesis have been proposed about the origin:

• acquired epidermal malformation,

• repetitive minor trauma,

• human papillomavirus (HPV) infection.

Occurence on dominant hands and involvement of thenar and hypothenar eminences suggest that CAH could be a reaction pattern to various stimuli.

The differential diagnosis includes Bowen’s disease, porokeratosis, squamous cell carcinoma, friction blister.

CAH is not easy to treat, but some cases have spontaneously resolved.