Genetics helps determine the general patterns on a fingertip, which appear as arches, loops and whorls. An individual finger can have just one of these patterns or a mixture of them.
While a fetus is developing, the ridges along these patterns are influenced by a number of factors, including bone growth, pressures within the womb and contact with amniotic fluid.
The patterns on a person's fingers, palms and feet are fully formed by roughly the fifth month of pregnancy.
They stay the same throughout life, barring any changes brought on by severe mutilation or a skin disease.