An assessment of factors influencing flexibility of human fingernails.

A new instrument has been developed and used to determine the effect of various materials on nail flexibility. It repeatedly flexes longitudinal nail sections through 90 degrees and records the number of flexions required to fracture each section. Immersion in water or a phospholipid-water preparation (PLW) greatly increases the flexibility of untreated and lipid extracted nails; immersion in mineral oil does not. Nail flexibility is directly related to the duration of their immersion in water. During water immersion, nail weight increases by 22% of its original weight within 2 h, and then decreases. The rapid increase in nail flexibility during water immersion is related to nail water content. It is possible to prolong the flexibility of previously hydrated nails by the application of PLW or mineral oil. PLW is more effective than water alone in prolonging flexibility of nails extracted with a mixture of acetone, water and acetic acid.