"Fearful sweat" samples were collected from male volunteers shown horror films.
Later, female volunteers were exposed to "fearful sweat". They then 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 facial expressions were ambiguous. It had no effect when the facial emotions were more certain.
This conclusion is consistent with what's been found with processing emotions in both the face and the voice. There, 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.
This is a direct behavioral evidence that human sweat contains emotional meanings.
They also demonstrate that social smells modulate vision in an emotion-specific way."
Smell is a prevalent form of social communication in many animals, but its function in humans is enigmatic. Humans have highly developed senses of sight and hearing. Why do we still need olfaction? These findings can offer insight on this topic. "The sense of smell guides our social perception when the more-dominant senses are weak
"Fear-related Chemosignals Modulate the Recognition of Fear in Ambiguous Facial Expressions"
Psychological Science, February