When and How Fingerprints Form
Every person, including individuals with an identical twin, has unique fingerprints. These fingerprints start forming in the 10th week after conception when some cells in the middle layer of the skin, called the basal layer, start growing faster than the cells in the inner layer of dermis or outer layer of epidermis. The extra cells cause the skin to buckle and fold into ridges.1 As the fingers grow, new ridges and branches form. Between 15 and 17 weeks after conception, a layer of keratin coats the surface of the skin. Smaller, secondary ridges form out of uneven keratin growth.
Any factor that can influence friction in the womb can influence a fetus’s fingerprint pattern. These factors include the density of the amniotic fluid, and the fetus’s size, location, and movement patterns.2 The pattern of fingerprints established by 17 weeks remains consistent as the child grows. 3