STUDENTS facing exams this month, take heart: your companions can smell your fear, and they empathise.

That's the implication of a study by Bettina Pause at the University of Dusseldorf, Germany, and colleagues. They put absorbent pads under the armpits of 49 university students an hour before they took their final oral exam and again as the same students exercised. Another set of students then sniffed the sweat samples while having their brains scanned.

None perceived a difference between the two types of sweat, but the pre-exam sweat had a different effect on brain activity, lighting up areas that process social and emotional signals, as well as several areas thought to be involved in empathy (PLoS One, DOI: 10.1371/journal.pone.0005987).

The researchers conclude that anxiety prompts the release of a chemical that bypasses conscious experience, automatically triggering similar feelings in anyone who sniffs it. This may allow fear to spread quickly and speed our ability to flee danger. A previous experiment found that sweat from skydivers activated anxiety circuits in sniffers' brains.

学生们本月要面临考试，鼓起勇气吧：你的同伴可以闻出你的恐惧来，他们也会产生同样的恐惧。

这是德国杜塞尔多夫大学的贝蒂娜·鲍丝与其同事所做一项研究的结论。他们在49位大学生参加期终口试之前，把吸水巾在学生的腋下放置一个小时，在这些学生参加书面考试之前再做同样的测试。另一组学生随后嗅闻这些取样的汗水，同时对这组学生的大脑进行扫描。

无人理解这两种汗水有何区别，但前一种考试的汗水对大脑活动的影响有所不同，它会使处理社会和情感信号的脑域兴奋起来，也会使若干被认为与同情有关的脑域兴奋起来。

研究人员得出的结论是，焦虑不安会引起一种化学物质的释放，这种化学物质绕过神志清醒的感受，可以自动触发嗅闻者的同类情绪。这可能让恐惧迅速蔓延，并让我们能够加速逃离危险。此前的实验发现，高空跳伞运动员的汗水会激活嗅闻者大脑中的焦虑神经。