It is a painful condition in which the side of the toenail appears to grow into the skin, or the side of the toenail grows over the ridge of the nail. Inflammation is a common side effect of ingrown toenails.
There are many different things that cause ingrown toenails. Curly toes or very large toes often result in ingrown toenails. An injury to the skin can also cause the edge of the nail to push into the skin. Incorrect trimming, incorrect shoes (especially with very narrow toes), very tight socks or stockings and frequent running can all cause this unpleasant condition.
South African Podiatry Association (SAPA)