Nail Anatomy and Disorders
Structures to name precisely
The nail plate is keratinized, translucent, and has no nerves. Beneath it lies the nail bed, which supplies color and sensation. The matrix produces the plate and extends under the eponychium (living skin at the base); the pale half-moon it shows through is the lunula. The cuticle is dead tissue on the plate at the base. The hyponychium seals under the free edge; sidewalls and nail folds frame the plate. Nails are appendages of the skin.
Growth facts
Fingernails grow roughly 0.1 mm a day - about one-eighth inch per month. Growth is faster in summer, in younger people, and on the dominant hand. A fingernail replaces in about four to six months; toenails take nine to twelve. Matrix damage shows as a permanent groove or ridge.
Disorders worth recognizing
Onychomycosis (fungal), paronychia (inflamed, often infected folds), onycholysis (plate separating from bed), leukonychia (white spots, usually trauma), koilonychia (spoon nails), onychorrhexis (splitting), Beau's lines (transverse grooves after illness), pterygium (forward-growing cuticle), onychophagy (biting), and subungual hematoma. Pain, pus, swelling, dark streaks, or unexplained discoloration mean refer to a physician - do not diagnose or treat.
Traps
Confusing cuticle with eponychium; assuming the lunula is always visible; calling a bruised nail a fungal infection; and recommending products for a condition that needs medical care.