Onychocryptosis (from Greek ὄνυξ onyx "nail" + κρυπτός kryptos "hidden"), also known as an ingrown toenail, or unguis incarnatus 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 may be overgrown toe skin. The disease starts from a microbial inflammation of the paronychium, secondary a to granuloma, and the result is a nail buried inside the granuloma. While ingrown nails can occur in both the nails of the hand and feet, they occur most commonly with the toenails. A true ingrowing toenail, or onychocryptosis, is caused by the actual penetration of the flesh by a sliver of nail. This should not be confused with other painful nail conditions such as involuted nails, or the presence of small corns, callus or debris down the nail sulci (grooves either side of the nail plate)or under the nail plate itself. Also it should not be confused with a similar nail disorder, onychocyrtosis (from Greek ὄνυξ onyx "nail" + κυρτός kyrtos "convex") or convex nail.