Nail Anatomy, Physiology, and Disorders
This domain checks whether you can identify nail structures, explain growth, and recognize disorders that require referral rather than cosmetic treatment. Exam questions often ask what a structure does or whether a nail tech should proceed.
Structures to know
- Nail plate: the hard keratin plate; it has no nerves or blood supply.
- Nail bed: skin beneath the plate, rich in blood vessels and nerves; it supports the plate.
- Matrix: the growth area under the proximal nail fold; it determines thickness, shape, and surface texture.
- Lunula: the visible whitish half-moon at the base, created by the matrix.
- Cuticle: dead tissue seal on the plate; eponychium is the living proximal fold. Do not confuse them.
- Hyponychium: seal under the free edge; lateral folds are sidewalls; mantle is the proximal fold pocket.
Fingernails grow roughly 3–4 mm per month; toenails grow more slowly. Growth slows with age and poor circulation.
Disorders and referral cues
Onychomycosis is a fungal infection; paronychia is inflammation or infection of the nail folds; onycholysis is separation of plate from bed; onychorrhexis is longitudinal ridging and brittleness; Beau's lines are transverse depressions from interrupted growth; koilonychia is spooning; melanonychia is a dark streak. Refer for spreading redness, pus, pain, sudden dark streaks, or unexplained separation. Green-black discoloration under an enhancement often suggests bacterial colonization and needs product removal and referral.
Worked example
A client has a dark band on one toenail that has widened over months. Do not file it or cover it with polish. Document what you see, decline service on that nail, and refer to a physician; a new or changing pigmented band is a medical concern.
Traps
Diagnosing a disease, cutting cuticle to "prevent" infection, and treating fungus with salon products are outside scope and cost marks.