It is said "eyes are the mirror of one's emotions," but scientists have now found that human sweat also contains emotional meanings.
Rice University psychologist Denise Chen has shown that when threatened, many animals release chemicals as a warning signal to members of their own species, who in turn react to the signals and take action.
The researcher says that a similar phenomenon occurs in humans as well.
It is already known that more than one sense is typically involved when humans perceive information, but the new study was taken up to know whether the smell of fear facilitates humans' other stronger senses.
For the study, Chen and graduate student Wen Zhou collected "fearful sweat" samples from male volunteers.
The volunteers kept gauze pads in their armpits while they were shown films, which dealt with topics known to inspire fear.
Later, female volunteers were exposed to chemicals from the "fearful sweat" when they were fitted with a piece of gauze under their nostrils.
When they viewed images of faces that morphed from happy to ambiguous to fearful, they were asked to indicate whether the face was happy or fearful by pressing buttons on a computer.
Exposure to the smell of fear biased women toward interpreting facial expressions as more fearful, but only when the expressions were ambiguous.
It had no effect when the facial emotions were more discernible.
The conclusion is consistent with what's been found with processing emotions in both the face and the voice.
An emotion from one sense modulates how the same emotion is perceived in another sense, especially when the signal to the latter sense is ambiguous.
"Our findings provide direct behavioral evidence that human sweat contains emotional meanings. They also demonstrate that social smells modulate vision in an emotion-specific way," said Chen.
He added: "The sense of smell guides our social perception when the more-dominant senses are weak."
The study has been published in the journal Psychological Science.