The Nail Unit: All the Parts You Need to Know
The nail unit is made up of several distinct structures. On the exam, you will be asked to identify each part and describe its function. Learn these cold.
Visible Structures
- Nail plate: The hard, visible portion of the nail. Composed of keratinized cells arranged in layers. This is what clients think of as "the nail."
- Free edge: The portion of the nail plate that extends past the fingertip. Filed and shaped during services.
- Lunula: The white half-moon at the base of the nail plate. It is the visible portion of the nail matrix and is most obvious on the thumb.
Underlying Structures
- Nail bed: The skin directly beneath the nail plate. Rich in blood vessels and nerves; gives the nail its pinkish appearance.
- Nail matrix: Located under the proximal nail fold. This is where nail growth originates. Damage to the matrix causes permanent nail deformity. The lunula is the visible part of the matrix.
- Hyponychium: The skin under the free edge where the nail plate separates from the nail bed. Acts as a bacterial barrier. Never push it back aggressively.
Surrounding Tissue
- Eponychium: The living skin at the base of the nail plate that overlaps the lunula. Do not confuse with the cuticle.
- Cuticle: Dead, colorless tissue attached to the nail plate surface. This is what you remove during a manicure, not the living eponychium.
- Lateral nail folds: Skin on either side of the nail plate. Protect the nail edges.
- Perionychium: All the skin surrounding the nail unit, including the folds and the hyponychium.
The nail matrix produces new nail cells. Damage to the matrix is permanent. The lunula is the visible part of the matrix, not a separate structure.
Nail Composition and Growth
Nails are composed of keratin, the same protein found in hair and skin. The keratin in nails is harder and more densely packed than in hair.
| Nail Type | Growth Rate | Notes |
|---|---|---|
| Fingernails | ~0.1 mm/day (3-4 mm/month) | Faster in summer, faster on dominant hand |
| Toenails | ~1-2 mm/month | Slower than fingernails; takes longer to regrow after loss |
| After matrix damage | Variable | May permanently alter plate shape or thickness |
A complete fingernail regrows in approximately 4-6 months. A complete toenail can take 12-18 months. Clients with slow-growing nails benefit from biotin-rich diets, though results are gradual.
Quick Structure-Function Summary
- Matrix: nail production
- Nail bed: support and blood supply
- Hyponychium: infection barrier at the free edge
- Cuticle: dead tissue removed during service (not the eponychium)
- Lunula: visible matrix, indicates active growth zone
Many students confuse the cuticle (dead tissue on the nail plate) with the eponychium (living skin at the base). You may safely remove cuticle. You must not cut the living eponychium, as it protects the matrix from infection.