How Fingerprints are Formed

By the 17th week of pregnancy, the fingerprints of a fetus are set. The uniqueness of fingerprints has been recognized and studied scientifically for two centuries, but researchers have not been able to explain exactly how they form. A new theoretical computer model describes how the patterns are likely created, beginning in the 10th week of gestation, when a fetus is about 3 inches (80 mm) long.

Researchers at the University of Arizona found that creation of the patterns involves stresses in a sandwiched sheet of skin called the basal layer. In a fetus, the basal layer grows faster than surrounding layers, the outer epidermis and the inner dermis. The basal layer buckles and folds in several directions, forcing complex shapes. Stresses are created at skin boundaries, including fingernails and knuckle creases, as well as around shrinking fingertip pads.

The fingerprint pattern is coded underneath the skin surface, does not change as we age, and the pattern cannot be destroyed by superficial skin injuries.

General characteristics of fingerprints can be inherited, so family members do tend have similar, but still unique fingerprint patterns. Even Siamese twins and identical twins have varying fingerprints.

Fingerprints are impressions made by the ridges on the ends of the fingers and thumbs. These ridges provide friction, or traction, when we grasp objects so that those objects do not slip through our fingers. Fingerprints are on the fingers and palms, but not on any other places of the skin. Scientists also believe that they may enhance our sense of touch.

Koalas have ridges on their fingers which create fingerprints very much like those of human beings.