(HealthDay News) -- When a toenail grows down and pushes into the skin, it's known as ingrown. Usually, the big toe is affected, but it can happen on any toe.

According to the U.S. National Library of Medicine, here are possible causes for an ingrown toenail:

• Shoes that are too tight or too loose.
• Toenails that are trimmed too short.
• Toenails that are trimmed with the edges rounded.
• Having thick toenails or difficulty trimming them.
• Tearing a toenail rather than trimming it properly.
• Having very large toenails or naturally curved toenails.
• Injuring the toe, such as by stubbing it.