When and How Fingerprints Form

Around week 12, the unborn baby’s tiny finger movements help shape the first skin creases near the joints. These creases guide where fingerprints will form.² At the same time, cells in the skin’s basal layer begin growing faster than surrounding layers, causing the surface to buckle into ridges.³ By week 13, these ridges start forming at the tips and centers of the fingers, then spread outward. By 15 weeks, each finger already shows its unique pattern of loops, whorls, or arches. Primary ridges are complete by 17 weeks, followed by finer secondary ridges. ⁴ By week 13, these ridges start forming at the tips and centers of the fingers, then spread outward. By 15 weeks, each finger already shows its unique pattern of loops, whorls, or arches. Primary ridges are complete by 17 weeks, followed by finer secondary ridges. As the skin matures, a protective layer of keratin forms between 22 and 25 weeks, refining these patterns.^{5 6} Curiously, ridges of the hands and fingers appear about 1 week earlier than those of the feet and toes.⁷ By 26 weeks, the baby’s fingerprints are fully set—unique and unchanging for life.⁸