An ingrown nail 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. While ingrown nails can occur in the nails of both the hands and the feet, they occur most commonly with the toenails (as opposed to fingernails) and, for the most part, are mainly problematic and painful on the big toe.
It is also known as onychocryptosis, from the Greek words ὄνυξ (onyx) ‘nail’ and κρυπτός (kryptos) ‘hidden’.
