Ingrown toenails are caused by the edge of the toenail turning down into the skin, causing pain from the pressure. The shape of the toenail can be inherited or influenced by shoe gear, activity, or trauma. If the nail penetrates the skin, it pushes bacteria into the skin causing an infection (redness, swelling, pus, drainage, odor).
Treatment for ingrown toenails is to have the ingrowing edge of nail removed permanently.
If the area has become infected, you doctor may need to temporarily remove the offending portion of nail in order to resolve the infection.