Eponychium

The eponychium is the living epidermal tissue located at the base of the nail, specifically forming the undersurface of the proximal nail fold.

It is responsible for producing the cuticle, which is the thin, non-living layer of keratin that adheres to the dorsal surface of the proximal nail plate and serves as a protective barrier against pathogens and environmental insults.

The eponychium is continuous with the skin of the digit and is distinct from the cuticle itself, which is its keratinized product. Histologically, the eponychium consists of stratified squamous epithelium and is supported by underlying connective tissue, with a vascular and neural supply similar to other periungual tissues.

The anatomical boundaries of the eponychium are defined proximally by the skin of the finger and distally by the start of the nail plate. It is situated above the nail matrix and is not involved in nail plate formation, but rather in the formation of the cuticle, which seals the potential space between the nail plate and the proximal nail fold.

This structure is clinically significant as disruption or removal of the eponychium can predispose to paronychia and other nail fold infections.