Nail fold
The proximal nail fold is similar in structure to the adjacent skin but is normally devoid
of dermatoglyphic markings and sebaceous glands. From the distal area of the proximal
nail fold the cuticle reflects on to the surface of the nail plate. The cuticle is composed of
modified stratum corneum and serves to protect the structures at the base of the nail,
particularly the germinative matrix, from environmental insults such as irritants, allergens
and bacterial and fungal pathogens.

Nail matrix
The proximal (dorsal) and distal (intermediate) nail matrix produces the major part of the
nail plate. Like the epidermis of the skin, the matrix possesses a dividing basal layer
producing keratinocytes; these differentiate, harden, die and contribute to the nail plate,
which is thus analogous to the epidermal stratum corneum. The nail matrix keratinocytes
mature and keratinize without keratohyalin (granular layer) formation. Apart from this,
the detailed cytological changes seen in the matrix epithelium under the electron
microscope are essentially the same as in the epidermis.
The nail matrix contains melanocytes in the lowest two cell layers and these donate
pigment to keratinocytes. Under normal circumstances pigment is not visible in the nail
plate of white individuals, but many black people show patchy melanogenesis as linear
longitudinal pigmented bands.

On the great toes, the nail matrix sits like a saddle on the distal
phalanx

Nail bed
The nail bed consists of an epidermal part and an underlying dermal part closely apposed
to the periosteum of the distal phalanx. There is no subcutaneous fat layer in the nail bed,
although scattered dermal fat cells may be visible microscopically. The epidermal layer is
usually no more than two or three cells thick, and the transitional zone from living
keratinocyte to dead ventral nail plate cell is abrupt, occurring in the space of one
horizontal cell layer. As the cells differentiate they are incorporated into the ventral
surface of the nail plate and move distally with this layer.
The nail bed dermal fibrous tissue network is mainly oriented vertically, being directly
attached to phalangeal periosteum and the epidermal basal lamina. Within the connective
tissue network lie blood vessels, lymphatics, a fine network of elastic fibres and scattered
fat cells; at the distal margin, eccrine sweat glands have been seen.

Nail plate
The nail plate is composed of three horizontal layers: a thin dorsal lamina, the thicker
intermediate lamina and a ventral layer from the nail bed. Microscopically it consists of
flattened, dead squamous cells closely apposed to each other. In older people acidophilic
masses are occasionally seen, called ‘pertinax bodies’.
The nail plate is rich in calcium, found as the phosphate in hydroxyapatite crystals; it is
bound to phospholipids intracellularly. The relevance of other elements which are present
in smaller amounts, such as copper, manganese, zinc and iron, is not exactly known.
Calcium exists in a concentration of 0.1% by weight, 10 times greater than in hair.
Calcium does not significantly contribute to the hardness of the nail. Nail hardness is
mainly due to dense sulphur protein from the matrix, which contrasts with the relatively
soft keratin of the epidermis. The normal curvature of the nail relates to the shape of the
underlying phalangeal bone to which the nail plate is directly bonded via the vertical
connective tissue attachment between the subungual epithelium and the periosteum.