Painful, reddened areas of skin along the edges of a nail indicate an ingrown nail. Some cases are very mild, with simple resection of the end of the nail offering relief, and more severe cases require local anesthesia, resection of a larger portion of the nail or entire nail plate, with the addition of oral antibiotics.
Treatments include soaking the affected foot in lukewarm water with Epsom salts or iodine liquid added before and often after treatment are a good idea.