Can Odorless Tears Have Chemical Effects on Other People?

Do tears only communicate emotions to someone who sees them? In a 2023 study, men who received women’s emotional tears through the nose showed a lower measure of retaliation during a monetary game. Odor ratings did not differ in a way that would indicate awareness of smelling tears, and responses were also found in olfactory receptors in cultured cells and in brain activity.

Investigating the chemical effects of tears at three levels

The study began with the question of whether chemical information in tears affects aggressive responses in humans. The researchers combined an experiment on men’s behavior, a cellular experiment using human olfactory receptors, and an experiment imaging the brain during the game.

Six women aged 22–25 donated tears collected while watching sad videos. The comparison liquid was saline trickled down and collected from the cheeks of the same women. This control also accounted for possible effects of contact with the skin of the cheek.

The first behavioral experiment recruited 31 men and analyzed 25 after exclusions for equipment problems and other reasons. Each participant attended at the same time on two consecutive days, receiving tears on one day and the control on the other. Order was counterbalanced across participants, and neither the participants nor the experimenters administering the procedure knew which liquid was being used: a double-blind design.

After sniffing the sample from a jar 10 times, participants played the game with a small sample-soaked pad attached beneath their nose. Ratings of odor intensity, pleasantness, and familiarity did not differ significantly between tears and the control, nor was there a clear difference from the ordinary saline sniffed at the beginning.

The retaliation-to-provocation ratio fell in the tears condition

In the game, participants could earn money by squeezing a ball. At intervals, an opponent took money from them; they could then choose to retaliate by reducing the opponent’s money without gaining anything themselves. Participants were told the opponent was another person, but it was actually computer-controlled.

The researchers’ measure was the number of retaliatory responses divided by the number of provocations received. Its mean fell from 1.67 in the control condition to 0.94 in the tears condition. This was a 43.7% reduction in the mean and was statistically significant. The frequently cited reduction of about 44% refers to this ratio in an experimental game.

In contrast, questionnaire analyses combining the two behavioral experiments found no significant condition differences in post-game impressions of the opponent, desire to meet him, or anger during the game. Changes in retaliatory behavior and self-reported feelings did not emerge in the same way.

Receptors responded despite little conscious perception of an odor

The researchers next tested 62 human olfactory receptors in cultured cells. An initial screen narrowed down the candidates, and retesting with progressively diluted tears identified concentration-dependent responses in four receptors: OR2J2, OR11H6, OR5A1, and OR2AG2.

This suggests that ordinary olfactory receptors may detect some component of tears. The active molecules, however, remain unidentified. Nor did the study establish that these four receptors caused the behavioral changes in men; it examined only a subset of human receptors.

Brain responses to provocation and connections between regions changed

In the third experiment, 33 separately recruited men played a similar game inside an MRI scanner. Behavioral analyses included 26 men, and brain-imaging analyses included 24. The retaliation measure was lower with tears, averaging 0.967 versus 1.306 for the control. The effect was smaller than in the first experiment, however, and yielded p = 0.048 in a one-tailed test examining the predicted decrease on the basis of that first experiment.

In this experiment, retaliation increased on the second day regardless of condition, and exclusions left unequal numbers in the two condition-order groups. Additional brain-activity analyses rebalanced the order groups, but these circumstances matter when assessing the strength of the behavioral replication.

Brain imaging showed smaller responses to provocation in the left anterior insula and prefrontal cortex during the tears condition. Condition differences in these responses were also associated with condition differences in the retaliation measure. Functional connectivity increased between the left anterior insula and a region extending from the right temporal pole into the amygdala and piriform cortex. Connectivity here is an analytical measure of how closely fluctuations in brain activity covary.

In other words, the finding was not simply that the whole brain became quieter. Activity decreased in regions responding to provocation, while their coordination with regions also involved in olfaction changed.

Implications for everyday life remain to be tested

The study examined women’s emotional tears received by men at close range to the nose. Effects in women receiving tears, effects of children’s or men’s tears, and effects at everyday distances remain questions for future research.

Hormones formed part of the study’s background, but the saliva collected in this study was not analyzed, and no measured change in testosterone was reported. The predicted changes in hypothalamic activity and connectivity were not found either. Gaps remain in the specific pathway linking receptors, hormones, brain activity, and behavior.

Summary

Men exposed to women’s emotional tears showed a lower measure of retaliation during a monetary game than in the saline control condition. A separate MRI experiment found a smaller behavioral effect in the same direction, together with reduced provocation-related brain activity and altered coordination with olfactory-related regions.

Cellular experiments also identified human olfactory receptors that responded to tears. By examining behavior, receptors, and the brain, the study explored how tears might serve not only as part of a visible emotional expression but also as chemical information received through the nose.

The research received support from the Israel Science Foundation, the US NSF and NIH, the Rob and Cheryl McEwen Fund for Brain Research, and other sources. The funders had no role in study design, analysis, or the decision to publish, and the authors declared no competing interests.

Reference

Agron S, et al. (2023). A chemical signal in human female tears lowers aggression in males. PLOS Biology, 21(12), e3002442. Original research article and open full text