Nails grow from an area of tissue called the nail matrix, located at the base of the nail just under the skin. Also known as the nail root, this region grows nails outward. Nails grow inward toward the skin from this area sometimes, either due to a birth malformation or eventual pressure from tight shoes or toe injuries. This is what is referred to as an ingrown toenail, although most people do not notice the ingrown nail until infection develops. By cutting the nail too closely, one does not cause an ingrown nail to form, as it has already formed at the root. However, this can irritate the skin next to the nail, leading to infection or inflammation of the skin which makes a typically painless ingrown nail become painful.