ELi5: Why does your body produce greenish phlem when you have a cold/flu?

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I’m sick right now and I’ve been coughing up a lot of large green chunks. Is my body creating it to fight off whatever’s happening, or is the cold causing the phlem? I’d love to know!

Google didn’t help me very much when I asked, it kind of just told me that I either had the flu, bronchitis, or cancer. ¯_(ツ)_/¯

In: 97

4 Answers

Anonymous 0 Comments

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.

(I copied this description off some website because I forgot the relevant enzyme and had to google. Can confirm it is correct though.)

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