Nail bed

The nail bed is the specialized structure of the nail unit located directly beneath the nail plate, extending from the hidden border of nail (distal edge of the lunula) to the hyponychium.

It consists of a thin, longitudinally ridged epithelium that is firmly attached to the underlying richly vascularized connective tissue, which in turn is anchored to the periosteum of the distal phalanx. The nail bed epithelium is distinct from the nail matrix, with a true basal layer and a suprabasal compartment that demonstrates limited proliferative activity under normal conditions, contributing minimally, if at all, to the nail plate in healthy adults.

The nail bed dermis is a relatively homogeneous compartment, lacking the complex compartmentalization seen in the matrix region, and is characterized by parallel longitudinal ridges that interlock with the ventral surface of the nail plate, providing strong adhesion between the two structures.

The nail bed is highly vascular, which imparts the pink color seen through the translucent nail plate, and contains specialized glomus bodies involved in thermoregulation.

At the distal end, the nail bed transitions into the hyponychium via the nail isthmus, a region with unique keratinization and attachment properties that help seal the distal nail unit and prevent onycholysis.