Anatomy, Physiology, and Nail and Skin Disorders
The nail unit
Know the matrix (produces the plate), nail bed, plate, cuticle, eponychium (living proximal fold), hyponychium, lunula, sidewalls, and free edge. Fingernails grow about 3 mm per month; toenails grow more slowly, about 1 mm per month. A fingernail replaces in roughly four to six months; a toenail may take nine to twelve months. Growth slows with age, illness, and poor circulation.
Common nail disorders
Onychomycosis is fungal; paronychia is inflammation or infection of the nail fold, often bacterial; onycholysis is separation of the plate from the bed; pitting is associated with psoriasis; Beau's lines follow trauma or systemic illness; koilonychia is spooning; leukonychia is white spotting; melanonychia is a dark streak that warrants referral. Skin conditions include contact dermatitis, viral warts, herpes, and bacterial impetigo.
Scope boundary
A nail technician recognizes and refers; does not diagnose or treat. Do not apply enhancements over inflammation, pus, open lesions, or suspected infection. Disinfect equipment after any service and discard porous items.
Traps
Questions call every discoloration “fungus,” confuse eponychium with cuticle, or ask you to recommend a medical treatment. Another trap is assuming a dark streak is always a bruise.
Worked example
A client has a dark band running from the cuticle to the free edge on one nail. Do not cover it with product; document it and refer for medical evaluation.