Fingernails normally grow at a fixed rate, but factors such as finger usage, age and injuries may cause fingernails to grow faster or slower, according to Wired. Despite some scientific research that shows fingernails grow at different rates, medical science has not determined why, notes WebMD.
William Bean of Walter Reed Army Medical Center measured his fingernail growth starting at age 32. Bean marked a spot on his nail, near the cuticle, and measured how far it traveled in a month. Over 20 years, the doctor discovered his rate of nail growth slowed as he got older, notes Wired.
Oxford dermatologist Rodney Dawber determined his finger wrapped in a splint following a rugby match grew 25 percent slower for three months while it healed, and then grew at its normal rate for three months following removal of the splint. Dawber did not determine whether the slow growth was from the injury or from lack of use, according to Wired. Dawber also noted the nails on his dominant hand grew faster than those on the other hand. These conclusions by Bean and Dawber led scientists to conclude that fingernail usage determines how fast they grow.
Despite these measurements taken by two notable scientists, fingernails do not generally grow faster at different times. Human fingernails grow approximately 1 millimeter per month, according to WebMD.