Denailing is the extraction of the nails from the fingers and/or toes, either as a medical procedure to treat severe nail infections, or as a method of torture. The United Nations Istanbul Protocol describes nail removal and the insertion of objects such as wire under the nail as forms of torture. Removed nails are capable of growing back normally over several months if the nail matrix is left intact through surgical extraction. However, if the matrix is damaged by trauma, it can result in an overgrowth of tissue from the proximal nail fold, resulting in the formation of pterygium. Particularly, if the nail matrix is burnt by a heated instrument, subsequent growth may produce nails which are striped, thin, or broken into longitudinal segments.
Medieval sources described the denailing interrogation process as conducted by laying the prisoner on a tabletop—securing the hands by chains around the wrists and the bare feet by chains around the ankles—and using a metal forceps or pliers—often heated red-hot—to individually grasp each nail in turn and slowly pry it from the nail bed before tearing it off the finger or toe. A more painful variant used in medieval Spain was performed by introducing a sharp wedge of wood or metal between the flesh and each nail and slowly hammering the wedge under the nail until it was torn free.
Another cruel variant involved using rough skewers of wood or bone dipped in boiling sulfur. A number of such skewers were slowly driven into the flesh under the prisoner's toenails. Alternately, the skewer was dipped in boiling oil, which served a dual purpose of both burning the incredibly sensitive flesh and lubricating the needle so that the torturer could freely explore a wide surface area beneath the toenail. When enough skewers had been driven home to pry each nail loose from its bed, the nail was torn out at the root with a pair of pliers. This was a favorite technique of torture in the German witch-hunter's arsenal, being extremely inexpensive, portable, and easy to inflict. It is also recorded that, in more recent times—particularly, during the Armenian genocide of the 1910s—phonograph needles were driven under fingernails and toenails to torture the prisoner before his nails were torn out with pliers.
In the aftermath of Italy's republican referendum after World War II, efforts to prosecute former officials in the Fascist government for collaborationism and war crimes resulted in the legal differentiation between the concepts of normal brutality, cruel brutality, and particularly cruel brutality. Only in the case of particularly cruel brutality would the accused be rejected for amnesty. Denailing was generally considered to fall under the first two categories, as for a brutality to be considered particularly cruel, it had to "horrify even those who are familiar with torture."
- Istanbul Protocol: Manual on the Effective Investigation and Documentation of Torture and Other Cruel, Inhuman or Degrading Treatment or Punishment (PDF) (Professional Training Series No. 8/Rev.1 ed.). New York and Geneva: United Nations. 2004. pp. 29–38. Retrieved 28 October 2016.
- A. Hirsch, ed., The Book of Torture and Executions (Toronto: Golden Books, 1944).
- G. R. Scott, A History of Torture (London: Merchant, 1996).
- Caroli, Paolo (2014). "The Role of the Judiciary Within the Construction of Collective Memory. The Italian Transition". Wroclaw Review of Law, Administration & Economics. 5:1: 169. Retrieved 28 October 2016.
- M. Donnelly and D. Diehl, The Big Book of Pain (Scroud, Gloucestershire, U.K.: The History Press, 2011).