Mucus has a commanding place in our collective imaginations. Although you may have heard some of the following factoids about the sticky stuff that lines your airways, there’s not much more than a good story to back them up.
• Milk thickens mucus. People believe this bit of biological trivia so strongly that they really do report thicker mucus after drinking dairy products. But close analysis by mucus ologists has found no change in the amount of mucus or its consistency after drinking milk. This myth may be partly reinforced by the creamy mouth-feel of milk, which can leave a coating on the tongue and throat.
• Green mucus signals a bacterial infection. Ordinarily, mucus is thin and clear.
As your body battles an infection of any kind—bacterial or viral—your mucus will thicken and become yellow or green. (The green color is actually from an ironcontaining enzyme your immune system uses for its germ-fighting reactions.)
• Blowing your nose to expel mucus shortens a cold’s duration. Keeping a clean nose may reduce the chance of transmitting your cold. (Or not, as your immune system may have already neutralized the virus.) However, forceful nose blowing can drive viruses and inflammatory substances into your otherwise germ-free sinuses, possibly setting the stage for a sinus infection.
Source of Information : Oreilly - Your Body Missing Manual