Onychocryptosis (from Greek ὄνυξ onyx “nail” + κρυπτός kryptos “hidden”), also known as an ingrown toenail, or unguis incarnates, is a common form of nail disease. It is an often painful condition in which the nail grows so that it cuts into one or both sides of the Paronychium or nail bed.
The common opinion is that the nail enters inside the Paronychium but, an ingrown toenail can simply be overgrown toe skin. The condition starts from a microbial inflammation of the Paronychium, then a Granuloma, which results in a nail buried inside of the Granuloma. While ingrown nails can occur in the nails of both the hands and the feet, they occur most commonly with the toenails.
A true ingrown toenail, or Onychocryptosis, is caused by the actual penetration of flesh by a sliver of nail.