Forget fingerprints—now there are sweatprints. Researchers have developed a polymer that changes color permanently from blue to red when exposed to water—even the small amount of moisture produced by the micrometer-sized sweat pores dappling a person’s fingertips; that makes the pores stand out clearly from the relatively dry areas surrounding them. Those pores, which lie along the miniscule ridges that help form fingerprints, render those prints more detailed (image), the researchers report online today in Nature Communications. The pattern of sweat pores on any particular individual is permanent, unchanging, and unique, so mapping these patterns could be useful for forensic identification, the team contends. Although high-resolution scanners can discern the pattern of pores, using the water-sensitive polymer would help distinguish active, moisture-producing sweat pores from inactive ones. And because sweat pores, for the most part, don’t switch from active to inactive, that distinction could help narrow identifications even further. Future research will reveal whether sweat pore mapping will be useful, the researchers say, but it’s possible that an individual could be identified from a fragment of fingerprint containing as few as 20 to 40 sweat pores.