Clear mucus is totally normal. The body naturally produces about 1.5 quarts of it every day — enough to fill a Breyer's ice cream container. It keeps your nasal passages lubricated and germ-free by acting as a moisturizing barrier against dehydration and foreign objects, including bacteria and viruses. But if the amount drastically increases, it could mean that you're suffering from allergies or the start of a cold or flu.
White mucus could mean a bunch of different things. Most often it means that your nasal passages are irritated and swollen, restricting mucus flow and causing it to dry out. This could be due to a nasal infection or a cold. But dairy products, allergies, and eating dehydrating foods such as coffee, tea, and alcohol can also turn your mucus white. Acid reflux or dry conditions may also be the culprit.
When you have an infection, whether it be a bacteria or virus, your immune system's white blood cells rush to the site to fight and destroy the pathogenic invader. After they've done their job and die, they're flushed out of your body with your mucus, and in the process can dye it yellow. Yellow mucus doesn't mean that you need antibiotics, but it means your body is fighting something; possibly a cold. At this point, you may want to wait it out and see if things don't improve after 10 to 14 days.
Your mucus can turn green from the even larger build up of dead white blood cells. This potentially means that your body is using many reinforcements to fight the infection, and perhaps it's losing the battle. This is especially true if your mucus has been green for a few weeks or longer. If that's the case, you should see your doctor; especially if you have a fever or feel nauseated.
Bloody mucus signals that there's a lot going on in your nasal passages, including dryness and irritation, and the tissues have become damaged. This results from any number of things, including allergies, infection, and lots of blowing or rubbing. Physical trauma — like walking into a wall, face-first — can also turn your snot red.
When blood from your nasal lining dries, it can mix with the mucus and turn brown. But brown mucus isn't always because of blood. It could also be dirt, dust, discoloration from cigarette smoke, snuff, or a spice. If you're coughing up brown mucus, though, you should see a doctor because this could be a sign of bronchitis.
Black mucus can materialize after inhaling dirt or dust; or after smoking cigarettes or marijuana. But it can also signal a serious fungal infection, especially if you have a compromised immune system. If your mucus is black for no obvious reason, you should see a doctor. This is especially true if you have a fever, chills, or have difficulty breathing.
