This condition has been found only in shoe-wearing cultures and does not occur in habitually barefoot people since it requires downward pressure on the nail by a shoe.
Causes may include:
Shoes cause bunching of the toes in the developmental stages of the
foot (frequently in those under 21), which can cause the nail to curl and
dig into the skin.
This is particularly the case in ill-fitting shoes that are
too narrow or too short, but any toed shoes may cause an ingrown nail.
Bad nail-care, including cutting the nail too short, rounded off at the tip
or peeled off at the edges instead of being cut straight across
Trauma to the nail plate or toe, which can occur by stubbing the toenail,
dropping things on the toe or going through the end of the shoes (as
during sports or other vigorous activity), can cause the flesh to become
injured and the nail to grow irregularly and press into the flesh
Predisposition, such as abnormally shaped nail beds, nail deformities
caused by diseases, or a genetic susceptibility gives rise to a higher
chance of an ingrown nail, but the ingrowth cannot occur without
pressure from a shoe.
Ingrown toenails may be the result of a bacterial infection, treatable with antibiotics.