When and How Fingerprints Form
Every person has unique fingerprints. Even people with an identical twin have unique fingerprints. These fingerprints start forming in week 12 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 17 and 19 weeks gestation, 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 19 weeks remains consistent as the child grows. 3