Onychocryptosis also known as an ingrown toenail, or unguis incarnatus is a common form of nail disease

Nail disease

Nail diseases are distinct from diseases of the skin. Although nails are a skin appendage, they have their own signs and symptoms which may relate to other medical conditions. Nail conditions that show signs of infection or inflammation require medical assistance...

. It is an often painful condition in which the nail

Nail (anatomy)

A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws, which are found on numerous other animals....

 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 may be overgrown toe skin. The disease starts from a microbial inflammation of the paronychium

Paronychium

Paronychium or the "lateral nail fold" is the term for the soft tissue surrounding the border of the fingernail or toenail. -Clinical significance:...

, secondary a to granuloma, and the result is a nail buried inside the granuloma.