Women may have a more subtle way of telling men “no” than anyone imagined. Chemical cues in their tears signal that they are not interested in romantic ac­­tivities, according to a study published online January 6 in Science.

Crying reveals a person’s mood, but its evolutionary origins have long been a mystery. Because emotional tears have a different chemical makeup than those evoked by irritants in the eye, cognitive neuroscientist Noam Sobel of the Weizmann Institute of Science in Rehovot, Israel, wondered whether emotional tears relay chemical mes­sages to others.

Sobel and his research team col­lected tears from self-professed “easy criers” as they watched sad movies. Later, the researchers held jars con­taining the odorless tears and pads that had been dipped in the tears under men’s noses.

These men rated female faces as less sexually attractive than did men who sniffed saline. Moreover, their sexual excitement dropped, as indi­cated by their own reports and by levels of testosterone in their saliva.

The researchers then scanned the men’s brains as they watched a tit­illating movie scene using functional MRI. Brain regions associated with sexual arousal showed less activity in men who sniffed tears compared with those who sniffed saline.

The findings represent the first evidence that human tears send chemical messages, Sobel reports. Because a decrease in testosterone levels is linked to reduced hostility, he speculates that weeping dampens not only the libido but also violent behavior. “If the signal really lowers aggression toward you, then the evolutionary value of crying is clear,” he says.