Symmetrical acral keratoderma (SAK), also known as acquired symmetrical acrokeratoderma, is a keratotic condition of the extremities notable for its symmetry, hyperpigmentation, macerating change with water exposure, and marked seasonal changes. The epidermal barrier function of the skin is also negatively affected, and both a moderate increase of transepidermal water loss (TEWL) and a moderate decrease of skin hydration with maintained elasticity have been reported as a result.

SAK is a rare condition, and its exact prevalence remains unknown. The disease most commonly affects young adult males of Asian descent, with a male-to-female ratio of approximately 9:1. While the typical age of onset is between 20 and 40 years, the condition can affect individuals of any age. SAK is reported to show some occupational correlation with Chinese factory workers in the tie-dye industry. About 10% of SAK cases have a familial history in reported cases.

The disease exhibits seasonal changes, tending to worsen and become aggravated during warm, humid summer months. Conversely, it shows spontaneous improvement or resolution during colder winter months.

The exact cause of this condition remains not fully understood. However, potential factors include mutations in the genes for filaggrin (FLG) and transcription factor 4 (TCF4). Analysis of the skin in both lesional and perilesional areas of SAK patients has demonstrated a decrease in the expression of aquaporin-3 (AQP3). This explains the observed rise in TEWL and the consequent reduction in skin hydration seen in SAK lesions. Additionally, increased melanin in the dermis, along with melanocytic proliferation, may contribute to the observed skin discoloration.

Ichthyosis vulgaris and palmar and foot hyperhidrosis are comorbidities that have been reported but have not been firmly established.

Other proposed names for this disease, which have not reached consensus, include "pigmented aqua-exacerbated symmetrical acral hyperkeratosis," "pigmented carpotarsal hyperkeratosis," and "hyperkeratosis nigricans carpi et tarsi."