Scientists will eventually be able to select tears by age and gender from the cryogenic repository

Credit: Thomas Fuchs

Compared with other bodily excretions, tears are vastly understudied. Collecting the salty drops is tedious – weepy donors are rare, men hardly ever sign up and tears must be “fresh” for their makeup to be properly analyzed. As a result, researchers lack a consensus about the purpose of a basic human behavior. Is crying a primal way to communicate that many species share, as some chemists hypothesize? Or is it, as psychologists have put forth, a uniquely human key to social bonding? Israeli neurobiologist Noam Sobel has a plan to advance the field: he has perfected a way to flash-freeze tears and is now working to create a “tear bank” for researchers around the world.

Sobel, who is based at the Weizmann Institute of Science in Rehovot, discovered in 2011 that women's tears contain pheromones that lower the testosterone levels of nearby men. But building on that research has been slow because the molecules easily degrade.

To keep the chemical composition of tears intact, Sobel and his team have developed a way to systematically freeze the droplets. The method involves liquid nitrogen, which rapidly lowers the temperature of a sample below −80 degrees Celsius. The process preserves most of the tears' chemicals, say the researchers, who plan to publish their results later this year. Next they will start building a cryogenic repository of tears, categorized by source and orderable online. “Just as other biobanks exist for amniotic fluid, blood and urine, we'll have a biobank of tears,” Sobel says. “This would let you do studies in two weeks instead of six months.”

A tear bank for research “has tremendous possibilities,” says Saad Bhamla, a bioengineer at Stanford University who often has to use animal tears in his own investigations into how tears create a film on the eye. As examples of applications, he points to Silicon Valley's interest in contact lenses that double as a heads-up display, among other functions, and the rising cases of dry eyes from prolonged sessions of staring at a computer screen.

Sobel hopes interested researchers will eventually be able to select tears by age and gender from the repository – say, 200 samples from white males, 18 to 25 years old. This customized access could expedite experiments tackling the chemistry of crying's many unanswered questions: Do tears affect mood or appetite? Do the tears of men and women differ? How do emotional and nonemotional tears – from, say, cutting onions – compare? For Sobel, the more people who cry their eyes out, the better.