Each individual nail grows at its own pace. Usually, the longer the outermost finger joint, the faster the nail grows. The nail of the index finger thus grows quickly, while the thumbnail grows the slowest, as the thumb lacks the central of the three ordinary finger joints.
On the toes, which are shorter than the fingers, the nails grow around three times as slowly. Moreover, the nails grow faster on the hand that a person normally uses more often. Observations show that the nails grow faster in the summer, and in those younger than 30.
Scientists don’t know why nails grow at different paces, but it may have something to do with the amount of blood — and thus the oxygen and nutritional substances — that reaches the cells at the bottom of the root of the nail. The cells of the nail root liberate the keratin protein, which settles under the nail and pushes it forward, making it grow.
Nail growth varies
A fingernail grows about a tenth of a millimeter a day and is fully replaced in three to six months. Toenails grow more slowly, so it may take up to 1.5 years before a toenail that has fallen off is replaced by a new one.