Happy, sad and angry do not even begin to cover the range of emotions we express in our faces, a study has found.

Using new computer software, scientists mapped no less than 21 emotional states, including apparently contradictory examples such as "happily disgusted" and "sadly angry".

The research more than triples the number of known emotional facial expressions.

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"We have gone beyond facial expressions for simple emotions like 'happy' or 'sad.' We found a strong consistency in how people move their facial muscles to express 21 categories of emotions, " said Dr Aleix Martinez, from Ohio State University, America.

"That is simply stunning. That tells us that these 21 emotions are expressed in the same way by nearly everyone, at least in our culture."

In future, the computer model could aid the diagnosis and treatment of mental conditions such as autism and post-traumatic stress disorder, said the researchers.

For centuries scholars have tried to understand how and why our faces betray our feelings. Until now they have focused on six basic emotions - happy, sad, fearful, angry, surprised and disgusted.

The new study saw 230 volunteers making faces in response to verbal cues designed to trigger emotional states, helping researchers find the new emotional states.