Ingrown nails are most frequently caused by cutting your toenails too short or rounding the nail edges or by wearing ill-fitting shoes or tight hosiery that press the nail into your toe. You can also get an ingrown nail after an injury, such as stubbing or jamming your toe.
If the condition causing the ingrown toenail continues, overgrowth of the tissue over the nail can lead to permanent changes in the tissue that can cause infection, more pain, and more swelling.