Sameera Nanabhay asked:
Do emotional or pain-induced tears differ?
Is it possible to test tears and deduce if they are related to physical pain or emotion, if so what is the difference between the
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.
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.