Anatomy, Physiology and Nail Disorders
The nail unit
Nail plate, nail bed, matrix, lunula, cuticle, eponychium, perionychium, hyponychium, lateral folds, free edge. The matrix makes the plate, so injury there leaves a permanent groove or ridge. The lunula is the visible part of the matrix. The nail bed carries nerves and blood vessels and will bleed; the plate itself has neither, which is why filing the plate does not hurt.
Growth
Fingernails grow about 0.1 mm per day - roughly 1/8 inch per month - replacing in four to six months. Toenails grow about half as fast, taking nine to twelve months. Growth slows with age, illness, cold and poor circulation. Expect a question on the slowest-growing nail, the great toenail.
Disorders to recognize, not treat
Onychomycosis (thickened, yellow, lifting), paronychia (red, swollen, painful folds - bacterial), onycholysis (plate separates from bed), onychorrhexis (splitting), onychauxis (thickening), leukonychia (white spots, usually trauma), koilonychia (spooning), pterygium, onychophagy (biting), ingrown nail, Beau's lines after illness.
The scope line
A technician may beautify and may recognize, but may not diagnose or treat. Redness, pus, a dark streak under the plate, sudden thickening or a new dark band means refer to a physician. Do not apply product over a suspected infection.
Traps
Confusing matrix with bed; calling the lunula 'the cuticle'; forgetting that a file used on a fungal nail is discarded.
Rule of thumb
If it is new, painful, discolored in a stripe, or oozing, it is a referral, not a manicure.