Why is snot green? © Getty Images

Why is snot green?

Healthy nose mucus is clear, but when your white blood cells have to fight off a cold, they produce a green-pigmented enzyme.

Asked by: Sam Evans, Poole

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Healthy nose mucus is clear, but when you have a cold, white blood cells called neutrophils are sent to fight the infection. One of the bug-killing enzymes they produce is called myeloperoxidase, which has a heme (iron-containing) pigment that causes the green colour in secretions such as pus and nasal mucus.


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