linguistic:voice_change, structural:expansion
Clinical significance

Healthcare and pre-hospital-care providers (EMTs or paramedics) often use the fingernail beds as a cursory indicator of distal tissue perfusion of individuals who may be dehydrated or in shock. However, this test is not considered reliable in adults. This is known as the CRT or blanch test. The fingernail bed is briefly depressed to turn the nail-bed white. When the pressure is released, the normal pink colour should be restored within a second or two. Delayed return to pink color can be an indicator of certain shock states such as hypovolemia.

Nail growth record can show the history of recent health and physiological imbalances, and has been used as a diagnostic tool since ancient times. Deep, horizontally transverse grooves known as " Beau's lines " may form across the nails (horizontal, not along the nail from cuticle to tip). These lines are usually a natural consequence of aging, although they may result from disease. Discoloration, thinning, thickening, brittleness, splitting, grooves, Mees' lines, small white spots, receded lunula, clubbing (convex), flatness, and spooning (concave) can indicate illness in other areas of the body, nutrient deficiencies, drug reaction or poisoning, or merely local injury.

Nails can also become thickened (onychogryphosis), loosened (onycholysis), infected with fungus (onychomycosis), or degenerate (onychodystrophy). A common nail disorder is an ingrowing toenail (onychocryptosis).

DNA profiling is a technique employed by forensic scientists on hair, fingernails, toenails, etc.