Nail and Skin Anatomy, Disorders, and Diseases
The nail unit
Nail plate, nail bed, matrix, lunula, eponychium (cuticle), hyponychium, lateral nail folds, and free edge. The matrix produces the plate, so matrix damage causes permanent distortion. The plate itself is dead keratin with no nerves or blood supply; the bed beneath it is sensitive.
Growth facts worth memorizing
Fingernails grow about 0.1 mm per day (roughly 3.5 mm per month) and fully replace in four to six months. Toenails grow about 1 mm per month and take nine to twelve months. Growth slows with age, cold, illness, and poor circulation.
Disorders a technician may see and serve
Leukonychia (white spots from trauma), onychorrhexis (ridging and splitting), onychophagy (biting), and mild Beau's lines. These are cosmetic and do not prevent service.
Conditions that must be referred
- Paronychia - red, swollen, painful, pus-filled nail fold; bacterial, refer.
- Onychomycosis - fungal infection with thickened, discolored, crumbly plate; refer.
- Tinea pedis - athlete's foot; contagious, refer.
- Onycholysis - plate separating from the bed; refer if the cause is unclear.
- Psoriasis, warts, koilonychia, melanonychia (a dark streak) - refer; a dark streak deserves urgent medical attention.
Green-black discoloration is often called "mold," but it is usually Pseudomonas bacteria thriving under a lifted enhancement. Never diagnose - describe what you see and refer.
Skin basics
The epidermis includes the protective stratum corneum; the dermis holds nerves, vessels, and glands. A callus is thickened stratum corneum from friction.
Rule of thumb
Red, hot, swollen, painful, pus, dark streak, or a separating plate → refer out.
Worked example: A client's toenail is yellow-brown and lifting. You do not file it thin or cover it - you explain that it needs a physician and you cannot service that nail today.