An ingrown toenail (also known as onychocryptosis or unguis incarnatus) occurs when the edge of the nail grows down and into the surrounding skin. It is a very common condition that can be very painful. The nail often grows so that it cuts into one or both sides of the nail bed. This can cause pain, redness, and swelling. If the nail punctures the skin, it may become infected and an abscess may form. Although the great toe is affect most commonly, any toenail can become ingrown.
Ingrown toenails are frequently caused by extra pressure on the toe, such as from shoes that fit poorly. They can also be caused by nails that are not trimmed properly. When the toenails are trimmed with rounded edges instead of straight across – it may cause the nail to curl inward and grow into the skin.