Ingrown toenails are known to physicians as onychocryptosis. They are common, painful conditions that occur when the skin on the side of a toenail grows over the edge of the nail, or when the nail grows into the skin.

Ingrown toenails can develop for many reasons. In some cases, the toenails are simply too large. Persons whose toes curl (congenitally or from disease such as arthritis) are prone to onychocryptosis. Trauma, such as stubbing a toe or having one stepped on can cause a piece of the nail to jam into the skin. Frequent running also can cause ingrown toenails. Ingrown nails can be caused by trimming them incorrectly, causing them to regrow into the skin, by excessively tight stockings, or by shoes with narrow toe boxes. Bedridden patients commonly develop ingrown toenails if the bedsheets are kept tucked-in tightly.

Click here for more information about ingown toenails from the Mayo Clinic.