Very rarely, and if so, only a tiny bit.(1) This is because death is not an instantaneous process. Even though someone’s heart may have stopped beating, followed by the death of brain cells, other cells that use minimal amounts of oxygen can survive a bit longer. Which means that not always, but in some cases, nails and hair might continue to grow a tiny bit.
The other important thing to consider here is that the skin of a person will shrink and retract after death. This, more than anything, can make it appear as if fingernails have gained substantial length since the person was last alive.
Debunking the Myth
Although the idea of fingernails continuing to grow after death is essentially 99.9% false, this notion has taken firm hold in popular culture.(2) Author Erich Maria Remarque is perhaps most responsible for feeding this false belief. In his World War I themed novel All Quiet on the Western Front, published at the end of 1928, a character imagined that his dead soldier friend’s fingernails continued to grow after death, in a morbid, corkscrew fashion.
But the truth is that the average human daily fingernail growth rate of a tenth of a millimeter stops dead in its tracks upon expiration. Funeral homes try to mitigate the appearance of this false condition with moisturizing creams and other substances designed to stop the aforementioned shrinkage.
Another important pop culture milestone for this false believe is the 1959 William Castle directed horror film The Tingler. The actor plays a pathologist who regularly conducts autopsies on prisoners, and during the film, he states that fingernails continue to grow after death. It’s simply not true, but thanks to the atmospheric nature of the film and Price’s skills as an actor, he—like author Remarque—was able to plant that seed in the public’s imagination.
(1) Focus Magazine – “Do Fingernails and Hair Really Keep Growing After Death?”, Retrieved October 16 2011 from http://sciencefocus.com/qa/do-fingernails-and-hair-really-keep-growing-after-death
(2) Snopes.com – Coffin Nails, Retrieved October 16, 2011 from http://www.snopes.com/science/nailgrow.asp