Proximal fold

The proximal nail fold is the soft tissue structure that forms the dorsal boundary of the nail unit at its base.

It consists of a dorsal (external) and a ventral (internal) surface. The dorsal surface is continuous with the skin of the digit, while the ventral surface, also known as the eponychium, is closely adherent to the nail plate for a short distance and gives rise to the cuticle, which is composed of the stratum corneum from both the dorsal and ventral aspects of the fold. The cuticle acts as a seal, protecting the nail matrix from external pathogens and trauma.

The proximal nail fold is composed of epidermis and underlying dense connective tissue, and it envelops the emerging nail plate, forming a pocket-like invagination with the nail matrix as its floor. This fold, together with the lateral nail folds, frames the nail plate and provides structural support and protection to the underlying nail matrix, which is responsible for nail production. The ventral aspect of the proximal nail fold is also recognized as a stem cell niche, particularly during embryogenesis, and plays a role in nail regeneration.

The microvasculature of the proximal nail fold is characterized by short, fine capillary loops, which are significantly shorter than those found in the nail bed or hyponychium.

The connective tissue of the proximal nail fold also serves as a suspensory system, protecting the nail matrix from biomechanical stress.