Anatomy, Physiology and Disorders of the Nail and Skin
This domain tests whether you know what nail structures do, how nails and skin grow, and - critically - which conditions you may work on and which require referral. The exam expects accurate terminology, not diagnosis.
Nail structures
- Nail plate (body): translucent keratinized cells, roughly 80 percent hard keratin, no nerve endings, no blood supply of its own.
- Nail bed: sits under the plate; capillaries show through as pink; attaches to the plate and is highly sensitive.
- Matrix: generates the plate; extends under the proximal fold. Injury here causes permanent ridges, grooves, or distortion.
- Lunula: the visible pale half-moon, the distal portion of the matrix.
- Eponychium (cuticle), lateral nail folds, nail grooves, nail root, hyponychium (the seal under the free edge), free edge.
Growth rates
Fingernails grow about 3 mm (1/8 inch) per month; toenails about 1 mm per month. A fingernail is fully replaced in 4–6 months, a toenail in 9–12. Growth is faster in warm weather, in younger clients, and during pregnancy; slower with age and poor circulation.
Skin basics
Epidermis (outermost stratum corneum), dermis (collagen, elastin, vessels, nerves, glands), subcutaneous layer. Skin protects, senses, regulates temperature, and synthesizes vitamin D.
Recognizing versus diagnosing
Refer for onychomycosis (thick, yellow, crumbling), paronychia (red, swollen, painful fold), onychocryptosis (ingrown edge), onycholysis (lifting without inflammation), Beau's lines, koilonychia, clubbing, and especially a new dark streak in the plate (melanonychia).
Worked example
A client's big toenail is thick, yellow-brown, and crumbling, with debris beneath the free edge. Reasoning: these are classic fungal signs. Do not apply an enhancement, do not aggressively thin the affected plate, refer the client to a physician, and discard every porous item and disinfect every nonporous tool that contacted the nail.
Traps
- Cutting out an ingrown nail - outside your scope and dangerous.
- Filing across the matrix, producing permanent grooves.
- Telling a client what condition they have instead of describing what you see and referring.