Anatomy and Physiology of the Nail and Skin
What the exam tests
This domain tests the structures of the nail unit and skin and their functions. Expect questions on the nail plate, nail bed, matrix, lunula, cuticle, eponychium, hyponychium, sidewalls, and free edge, plus basic skin layers and nail growth. You must use the terms correctly rather than repeating common salon mislabels.
Core structures
- The nail plate is the visible hard keratin structure; it has no nerves or blood supply in the visible portion.
- The nail bed lies beneath the plate and contains blood vessels and nerves.
- The matrix produces the nail plate; the lunula is the visible portion of the matrix.
- The cuticle is dead stratum corneum that seals the proximal nail fold to the plate; the eponychium is the living skin at the proximal fold.
- The hyponychium is the seal under the free edge; sidewalls are the lateral nail folds.
- Fingernails grow about 3 to 4 mm per month; toenails grow more slowly, about 1 mm per month.
Worked example
A client points to the living tissue at the base of the nail and calls it the cuticle. You explain that the true cuticle is the thin dead tissue on the plate, while the living fold is the eponychium. You do not cut the living tissue; you gently push back only the nonliving cuticle and soften it with product. The reasoning is anatomical: the eponychium is a living seal, and injuring it increases infection risk.
Traps
Calling the lunula the cuticle. Saying the nail plate grows from the nail bed. Cutting the eponychium because it looks like cuticle. Filing the nail plate until it loses structure.