Ingrowing toenails happen when a piece of nail presses into the skin of the toe. It is most common in big toes but can also affect the smaller toes. Ingrowing nails can be extremely painful and can bleed, become inflamed or infected.
Not all painful toes are caused by ingrowing toenails piercing the skin. Nails that are very curved (involuted) but do not pierce the skin, may not be ingrowing, but can be just as painful. Pain may also be caused by thickened or curved nails, or even a corn under the nail.