Studies have revealed that people with autism react abnormally to social chemical signals

A study published online November 28th in nature
-neuroscience shows that ASD patients react differently, sometimes in the opposite way, to the sociochemical signals of unconscious perception than individuals without autism spectrum disorder (ASD). The findings may partly explain why ASD patients misread emotions.
mammals often interpret emotions by smell and communicate socially through their knowledge of chemical signals. There is growing evidence of the same meaningful release of social chemical signals in humans. Human chemical signals have been shown to convey information about age, hostility, happiness and fear, which can potentially affect brain activity and general mental and emotional states.
noam Sobel of the Weizmann Institute of Science in Israel and colleagues found that unconscious contact with "fear smells" - such as sweat secreted by skydivers in stressful states (based on cortisol levels) - increased activity in the plant nervous system (responsible for unconscious body functions such as breathing and heartbeat) in neurofunscient individuals, but did not affect ASD patients.
researchers also found that neurofunscical individuals trusted mannequins that secrete sweat when walking calmly, rather than erratic models that release this fear chemical signal. But participants with ASD reported more trust in models that emit a "smell of fear." In addition, unconscious contact with two different synthetic chemical signals had the opposite effect on participants with normal neurological function and participants with ASD.
Sobel et al. found that both groups had normal sense of smell because when asked to distinguish and judge body odors, their answers were almost the same, and only chemical signals that came into contact with them reacted differently.
the authors speculate that abnormal reactions to chemical signals have a deeper effect than non-reactions, as abnormal reactions can lead to misreading of emotional signals. (Source: Zhang Zhang, China Science Daily)