Scientists have studied the process of formation of fingerprints

Fingerprints are unique and remain for life. They have been used to identify people since the 1800s. Several theories have been put forward to explain how fingerprints form, including spontaneous folding of the skin, molecular signals, and the idea that the ridge pattern may follow the location of blood vessels.

Scientists knew that the ridges that characterize fingerprints begin to form as ridges of skin that run down, like grooves. Over the next few weeks, the rapidly proliferating cells begin to grow upward, resulting in thickening of the skin bands.

Because incipient fingerprint crests and developing hair follicles share similar downstream structures, the researchers in the new study compared cells from the two locations. The team found that the two sites shared several types of signaling molecules—messengers that transmit information between cells—including three known as WNT, EDAR, and BMP. Further experiments showed that WNT tells the cells to proliferate by forming protrusions on the skin and produce EDAR, which in turn further increases WNT activity. BMP disrupts these actions.

To investigate how these signaling molecules might interact to form patterns, the team adjusted the levels of the molecules in mice. Mice don’t have fingerprints, but their toes have striated bumps on the skin that can be compared to human fingerprints. “We turn the dial — or the molecule — up and down, and we see the pattern change,” says biologist Denis Headon of the University of Edinburgh.

Increasing EDAR resulted in thicker, more widely spaced ridges, while decreasing it resulted in spots rather than streaks. The opposite happened with BMP, as it interferes with the production of EDAR.

This switching between stripes and patches is a characteristic change seen in systems driven by Turing reaction-diffusion, says Hedon. This mathematical theory, proposed in the 1950s by British mathematician Alan Turing, describes how chemicals interact and propagate to create patterns seen in nature. Although during the inspection, it explains only some regularities.

However, mouse fingers are too small to create the complex shapes seen in human fingerprints. So the researchers used computer models to simulate a Turing pattern spreading from three previously known sites of onset on the fingertip: in the center of the finger pad, under the nail, and in the joint crease closest to the fingertip.

By varying the relative timing, location, and angle of these starting points, the team was able to create each of the three most common fingerprint patterns—arches, loops, and curls—and even rarer ones. For example, arches can form when the protrusions of the pads of the fingers begin to slow down, allowing the protrusions that begin at the crease and under the nail to take up more space.

“This is a very well-done study,” says developmental and stem cell biologist Sarah Millar, director of the Black Family Stem Cell Institute at the Icahn School of Medicine at Mount Sinai in New York.

Controlled competition between molecules also determines the distribution of hair follicles, says Millar, who was not involved in the work. The new study, she said, “shows that the formation of fingerprints follows some basic themes that have already been developed for other types of patterns that we see in the skin.”

Millar notes that people with gene mutations that affect WNT and EDAR have skin abnormalities. “The idea that these molecules might be involved in fingerprint formation has been floating around,” she says.

In general, Headon says, the team aims to help the formation of skin structures, such as sweat glands, when they don’t develop properly in the womb, and possibly even after birth.

“What we want to do, more broadly, is understand how the skin matures.”