Nail Structure, Disorders, and Diseases
Build the nail in order
Matrix → nail plate → nail bed → lunula (visible matrix) → eponychium/cuticle → sidewalls (lateral folds) → hyponychium (the seal under the free edge) → free edge. The matrix makes the plate, the bed supports it, and the hyponychium keeps pathogens out. Fingernails grow about 1/8 inch (3 mm) per month and fully replace in roughly 3–6 months; toenails grow about 1 mm per month and take 9–12 months. Growth is faster in summer, on the dominant hand, and in youth.
Vocabulary the exam loves
Onychocryptosis (ingrown), onycholysis (loosening), onychomadesis (separation at the base), onychauxis (thickening), onychorrhexis (brittle, split nails), onychophagy (biting), paronychia (infection of the fold), onychomycosis/tinea unguium (fungal), Beau's lines (transverse grooves after illness), leukonychia (white spots), koilonychia (spoon nails), pterygium (forward creep of the eponychium), melanonychia (dark streak).
Infectious vs non-infectious
Bacterial (paronychia, green nails), fungal, and viral (warts) conditions are contagious - do not service, refer to a physician, and disinfect everything. Ridges, spots, and brittleness are usually non-infectious and may be served.
Trap watch: a nail technician never diagnoses. Describe what you see, note it in the record, and refer.
Rule of thumb: if it is red, swollen, painful, oozing, or has a dark streak under the plate, stop and refer.