Tears are traditionally judged to be a visual display of emotion, and humans, it's claimed, are the only species to shed them. But now scientists in Israel have found that they can also carry chemical messages to alter the moods of others close by, an observation which fits with earlier studies showing that the composition of emotionally-shed tears differs significantly from the composition of tears produced in response to eye irritation.
The new discovery, published in Science, was made by Edith Wolfson Medical Centre researcher Shani Gelstein and her colleagues. They showed two female volunteers some tear-jerking film footage and collected the watery results as they ran down the womens' cheeks. In a separate experiment they also collected saline solution dribbled down the same womens' cheeks to control for any odours that might be entering the tears from the skin.
These tear samples were presented in a blind fashion to the nostrils of 24 male volunteers who were asked to rate the sexual attractiveness of a series of female subjects shown in a collection of photographs. The photographs were viewed twice, once while the subject was smelling the saline control and again during exposure to the emotional tears. The researchers also measured the mens' testosterone levels during the study as an indicator of arousal.
Seventeen of the volunteers rated the same female faces as significantly less attractive when they viewed them whilst sniffing the tears compared with the saline. The subjects also had lower testosterone levels following tear exposure, and brain scans also showed a drop in neuronal activity in brain regions linked to mood when subjects sniffed the tears.
This suggests that, contrary to the prevailing view that tears are merely an outward display of emotion, in fact it appears that they also contain covert chemical signals that convey mood-altering messages to male recipients. The team point out that there is ample opportunity for such signals to pass from a teary-person to a recipient. "We hug a crying loved one, often placing our nose near teary cheeks, typically generating a pronounced nasal ihalation as we embrace."
However, the identity of the chemicals responsible for these effects remains a mystery, as does whether mens' or childrens' tears are capable of similar emotional chemicals manipulation...