Nail Structure, Growth, and Recognizable Disorders and Diseases
Structure you must be able to label
The nail plate is the hard keratin surface; it rests on the nail bed. The matrix extends under the proximal fold and produces the plate, so matrix damage shows up as a permanent groove or distortion. The lunula is the visible part of the matrix. The cuticle is dead tissue clinging to the plate; the eponychium is the living skin at the base - you may gently push the cuticle, you may not cut living tissue. The hyponychium seals under the free edge, the sidewalls are lateral folds, and the nail groove holds the plate.
Growth
Average fingernail growth is about 1/8 inch (roughly 3 mm) per month; a fingernail replaces in 4–6 months, a toenail in 9–12. Growth is faster in summer, on the dominant hand, and in youth; slower with age, poor circulation, or illness.
Disorders to recognize (not diagnose)
Onychophagy (biting), onychorrhexis (splitting), leukonychia (white spots, usually trauma), koilonychia (spoon nails), pincer nails, eggshell nails, Beau's lines, and agnail (hangnail) are noninfectious. Paronychia (red, swollen, pus at the fold), onychomycosis/tinea unguium, tinea pedis, and green discoloration from Pseudomonas are infectious or medical - refer out and do not service.
Traps
Mixing up cuticle versus eponychium; claiming a technician can treat fungus; calling leukonychia a calcium deficiency; saying toenails grow as fast as fingernails; servicing a red, swollen fold.
Rule of thumb
Red, swollen, pus, green, or lifting plate = stop, refer, document. Worked example: a client has a green-black spot on one nail. Do not file over it or cover it; explain it is not a stain you can treat, refer to a physician, and reschedule after clearance.