Is it true that human tears are completely sterile? If so, why?
by 
Daydreamer
ANSWERS: 3
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Human tears are sterile although I cannot offer an explanation as to why.
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Human tears are completely sterile because they contain the salts that the human body produces. Contact solution is sterile therefore tears must be sterile since they are made of the same components.
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I wouldn't expect them to be completely sterile, but tears do contain some anti-bacterial elements - lysozymes and defensins. Lysozymes kill certain types of bacteria, called "gram-positive bacteria" but they do not kill gram-negative bacteria, yeast, fungi, or viruses. Defensins have some effect against viruses, bacteria and fungi but not against yeast. Still, even the combination of these two agents couldn't be expected to keep an eye completely sterile. People do get eye infections after all - conjunctivitus (pink eye) for example. So tears do have some sterilizing properties, but I would not trust them to be completely sterile. The answer below describing tears as completely sterile because they have salts is not correct. The oceans are plenty salty, and they are teeming with microbes. Contact solution is sterile because the manufacturer sterilizes it, not simply because it contains salts, thought salts may help.
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