Anatomy, Physiology and Nail Disorders
Structure
Nail plate (keratin, no nerves or blood vessels), nail bed, matrix (where growth is produced - injury here shows as a lasting groove), lunula (visible portion of the matrix), eponychium and cuticle (the seal at the base), hyponychium (seal at the free edge), nail folds and grooves, free edge. Beneath the plate, the bed's dermis carries blood vessels and nerves. Around the hand: phalanges, tendons, and the median, ulnar, and radial nerve and blood supply.
Growth
Fingernails grow about 0.1 mm per day, roughly 3 mm (1/8 inch) per month, so full replacement takes about four to six months. Toenails are far slower, nine to twelve months. Growth slows with age, poor circulation, illness, and cold.
Conditions versus disorders
A condition is a variation you can work around or note. A disorder requires medical referral, and you may not diagnose or treat. Refer for yellow-brown or green-black discoloration, separation (onycholysis), swelling, redness, pain, pus, dark streaks (melanonychia), pitting, or severe thickening.
Terms to recognize
Onychomycosis (fungal), paronychia (bacterial fold infection), onycholysis (separation), onychorrhexis (splitting), onychauxis (thickening), leukonychia (white spots), koilonychia (spoon nail), pterygium (forward-growing fold tissue), hematoma (blood under the plate).
Traps
"Cuticle and eponychium are the same" - the cuticle is the thin layer; the eponychium is the fold. "The matrix is the white half-moon" - that is the lunula. "You can treat fungus with antiseptic and continue" - refer.
Rule of thumb
If it hurts, is hot or swollen, oozes, or changes color and thickness, stop the service and refer.