The sight of someone in tears might make you feel concerned. But the smell of tears, researchers say, has a different effect.

“You might think—we did—that [smelling] tears might create empathy,” says Noam Sobel, a neurobiologist at the Weizmann Institute of Science in Israel. He and his colleagues had women watch a sad movie scene, collected their tears and placed samples of the unidentified fluid under men’s noses. The tears did not elicit empathy in a standard lab test, but they did reduce the men’s sexual arousal and testosterone levels. Apparently the tears sent a message that romance was off the table.

This study offers some of the most recent evidence that people perceive all sorts of interesting things about one another through olfaction. Airborne molecules that elicit a reaction in a member of the same species are called pheromones, and the most famous ones are potent aphrodisiacs, like androstenone and androstenol in the saliva of male boars. If a fertile female gets a whiff of these molecules, she’ll present her rear to the male, a universal gesture in wild pig patois that means, “Let’s start a family.”

Researchers (as well as fragrance companies) have been hoping to find a human sex pheromone for decades, but so far the search has failed, says George Preti of the Monell Chemical Senses Center in Philadelphia. “That doesn’t mean a human sex pheromone doesn’t exist,” Preti is quick to add. “It just means we haven’t found one yet.” In fact, some researchers suspect that if there is a turn-off pheromone, as Sobel’s team says, there’s likely to be a turn-on pheromone.

In one 2005 study, gay men given anonymous samples of sweat preferred the scent of gay men, and heterosexual men fancied the scent of women. One’s nose can also help identify a genetically compatible mate. Researchers asked women to rate the odors of T-shirts worn by different men. Women preferred men whose DNA was different enough from their own that it would increase the likelihood of producing a child with a robust immune system.

Newborns preferentially scoot toward the scent of breasts. And adults can often tell by smell whether the person who produced perspiration was anxious or not.

The search for human pheromones has been hampered by two obstacles. First, “the effects we see are not dramatic,” Sobel says. Instead, Preti says, our responses to odors are “confounded by other sensory inputs like sight and sound, past experiences, learning, context—and not to mention laws.”

Second, nobody has been able to find the exact chemicals that cue people about anxiety, mating compatibility or breast milk. This may be because researchers have traditionally analyzed aromatics from armpits. The fact is, any bodily fluid could potentially harbor pheromones, which is why Sobel studied tears of sadness. And who knows what signals are lurking in tears of joy?