Do emotional and pain-induced tears differ?

18 August 2014
Presented by Georgia Mills.

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Humans are the only animals that cry tears of emotion as well as pain. But does each type of tear differ in its chemical composition, and can you tell why someone was crying from looking at this?

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Crying

00:00 - Do emotional or pain-induced tears differ?

Can you tell why someone was crying just from looking at their tears? And why do people get so watery-eyed in the first place?

Do emotional or pain-induced tears differ?

Professor Vingerhoets - Crying predominantly expresses powerlessness or the strong desire to be reunited with a lost valued person, object or location. The advantage of crying aloud is that it is emitted in all directions. It is then very likely to be heard by parents, who can provide care, but this means it may also be heard by predators. Most mammal offspring will make distress calls if separated from their carers, however humans are the only species who shed emotional tears. The advantage of crying tears, a visual signal, is that it cannot be detected in the same way by predators but may easily be seen by the parents or caregivers.Physical pain tears and emotional tears are both produced by the same glands in the eyes. Like other glands (such as salivary glands or sweat glands) they are connected to our blood stream. Some ingredients of the tears originate from the blood, and the composition of blood can be effected by your hormones, which in turn are affected by stresses and your emotional state. This could lead us to think that tears produced in different emotional states could differ in their composition. However, a great deal of mystery still surrounds this idea. Over 30 years ago, American researchers compared the biochemical composition of emotional and irritant (onion) tears and found that the emotional tears contained more proteins. However, that has never been replicated and we do not know what this would mean.

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