Fearful expressions not just reflect your emotions but also improve your ability to detect danger, according to a new research.
A look of fear is characterised by wide eyes, raised eyebrows and flared nostrils.
The findings lend support to an idea first laid out by Charles Darwin that facial expressions of emotion were often remarkably similar across human cultures, and even the animal kingdom, implying they may have a common evolutionary benefit.
Researchers from the University of Toronto, Canada, have now produced evidence that suggests he was right. Dr Joshua Susskind and colleagues found that fear expressions increased range of vision, speeded up eye movements, and got more air into the nose.
In one experiment, study participants had to identify when a dot entered their visual field, while they maintained fearful, neutral or disgusted expressions.
In another, also with these expressions, they had to move their eyes as quickly as possible between two targets about 30 centimetres apart on a computer screen while their eyes were tracked.
The amount of air that could be breathed in while showing fear and disgust was also measured.
In each case, the researchers found, the expression of fear - or the "Home Alone face", as Susskind nicknames it - let significantly more of the world in.
The open eyes allowed quicker detection of objects on the periphery, as well as faster eye movements back and forth, while an open nose took in more air with each breath without any extra effort. An MRI scan confirmed the difference in the space in the nasal cavity.
"These changes are consistent with the idea that fear, for example, is a posture towards vigilance, and disgust a posture towards sensory rejection," New Scientist quoted Susskind, as saying.
Further experiments, he says, will explore to what extent the brain actually uses this extra information to enhance performance.
The study is published in Nature Neuroscience.