Nail Anatomy, Disorders, and Diseases
Structures to know
The natural nail unit includes the nail plate (the hard keratinized portion), the nail bed (skin beneath the plate), the matrix (where new cells form; damage here causes permanent grooves or ridges), the lunula (visible whitish half-moon at the base), the cuticle/ eponychium (living tissue at the base that should never be cut), the sidewalls, the hyponychium (seal under the free edge), and the free edge. The nail plate is made of keratin and is nonliving; the tissue around it is living.
Disorders vs. diseases
A disorder is a condition that is not infectious and can often be worked over or referred: beau's lines (transverse grooves from trauma or illness), koilonychia (spoon nails), onychorrhexis (splitting), onychauxis (thickening), leukonychia (white spots), paronychia (inflamed tissue around the nail - often bacterial, so refer), and ingrown nails.
A disease is infectious or systemic and must be referred, never serviced: onychomycosis (fungal), paronychia with pus, pseudomonas (green discoloration under artificial nails), warts, herpes whitlow, and any red, swollen, or draining area.
Traps
Questions blur the line between a disorder you may cosmetically improve and a disease you must refuse. Green nails, pus, and spreading redness are always referrals. Do not cut living tissue (eponychium).
Rule of thumb
If it is contagious or open, stop and refer. If it is cosmetic or mechanical (ridges, splits, thickening), you may proceed with care and document.