Snot

Back ache, flu, head aches are all bearable. The common cold is not. Snot. Geddit? Okay stop with the school boy humour. Whilst recovering from a cold. It takes forever to get rid of the stuff, I blew into my handkerchief and noticed the exceptionally green stuff that came out. Almost emerald in colour. Then I asked myself, "why so?". Here is the answer:

"The green colour is due to immune cells called neutrophils. These are the first cells to appear when bacteria start infecting the nasopharynx. Neutrophils will engulf the bacteria (phagocytosis) and begin to destroy them within themselves using potent digestive enzymes (amongst other things, another being hydrogen peroxide). One of these is lactoferrin and other enzymes are dependent on iron for their activity. The colouration therefore comes from the iron. Ferrous iron compounds are green. It turns yellow the bacteria have been around for a while and other cells start moving in and dying "

There you are. An explanation by a doctor from Wales. For another angle on snot, I found an australians explanation for snot as follows:

"It is not so much the snot which is green as the phlegm component, and this is only when it is infected. Neither healthy snot nor phlegm is really green. It becomes so in the presence of infection because of the large numbers of white blood cells present, which make their way through the airway walls to combat the infection. They also give pus a whitish-green colour. So it should be white but it's snot."

Of the two explanation's I can confidently say that the second description will put me off food for a while.