why is snot green?

[justvicky]

... or yellow?

[dosset]

why is poo brown

[justvicky]

Ah, I know this one! Poo is brown because it is a mixture of degraded haemoglobin from blood (red) and bile (green). Newborn babies poo is green because they haven't degraded any haemoglobin yet. Nice!

[stevie21]

Vicky - that's absolutely disgusting but strangely impressive that you know this!

[johntheplamf]

And why is belly button fluff Blue??

[Clanad]

After all that, your question still wasn't answered... so...The green colour comes from immune cells called neutrophils. When you get a cold these neutrophils engulf the bacteria and begin to destroy them using digestive enzymes. Some of these enzymes, such as lactoferrin, are dependent on iron for their activity. The colouration comes from the iron - ferrous iron compounds are green. After a while, snot turns yellow as other cells start moving in and dying.
In the nose, mucous acts as a barrier against germs, dust and other noxious substances. We breathe between 10,000 and 30,000 litres of air each day - which carries pollen, germs and a great deal of other gunk. These get trapped in the mucous surface and destroyed by white cells and enzymes.  More than you ever wanted to know... (With help from bbc.co.uk)

[justvicky]

Thanks, Clanad. I thought someone must know! It's just I've heard two different explanations - one was yours about the iron enzymes, the other one was that it was a mixture of Staph. aureus bacteria (yellow) and Pseudomonas (green I guess) bacteria. Maybe the bacteria contain iron enzymes too??

[Gef]

Reminded me of the old joke. "What's the difference between snot and Brussels sprouts?" Answer - "Boys don't eat Brussels sprouts!"