When you catch a cold and mucus production goes up, sinuses may also get blocked, so these cavities can get overgrown with bacteria that might lead to a sinus infection.
But, according to Metson, people with a cold are not most contagious to others when they are producing the most mucus. "The volume of mucus doesn't correlate with the number of viral particles shed."
Rather, Metson suggested that your level of contagion is more closely linked with where you are in the cold cycle. "People are shedding the most viral particles early on in a cold -- when you are incubating the virus and having early symptoms."
Interestingly, Metson noted that sneezing was once thought to be the main cause of a cold spreading, but now scientists think it has more to do with hand-to-hand contact with the virus.
As for what causes those clumps of mucus, also known as "boogers," Metson explained it this way: When people breathe in, especially during the winter, they're inhaling drier air. This dries out mucus found in the front of the nose, forming a nasal crust.
Want to ease up on boogers as well as unclog a stuffed-up nose? The treatment most often recommended was nasal irrigation, or rinsing out your nose with a salt-water solution, ideally twice a day.
"I like to tell my patients, you brush and then flush," advised Metson. In other words, after brushing your teeth, you then flush out your nose with a glass of warm water and a teaspoon of salt delivered via a bulb syringe, neti pot or squeeze bottle found in nasal rinse kits sold at pharmacies.
You probably think of mucus as the substance that tends to come out of your nose, and phlegm as the stuff that come out of your mouth.
In medical speak, the term phlegm is interchangeable with sputum, and "all of it is mucus," explained Marshall.
Phlegm is a mixture of mucus and saliva and white blood cells produced by the body in response to inflammation. It brings moisture to the area and helps your body clear away infection.
And since there are mucous membranes lining the nose and sinuses, as well as the throat, esophagus, lungs and even the stomach, there's plenty of mucus around to form phlegm.
Smokers and people with a cold or lung conditions, such as emphysema or chronic obstructive pulmonary disease, produce more phlegm. Experts say that drinking milk doesn't necessarily cause your body to make more phlegm, but it may make what's there thicker and more annoying to your throat.
If phlegm gets darker in color in people with lung conditions, it could mean an infection. And sometimes, blood might discolor phlegm from coughing or a bad infection, or if it continues to occur, possibly a tumor, according to Marshall.
If you're hacking up gobs of phlegm, your best bet is to thin them out by drinking plenty of liquids -- hot or cold. Steamy, warm soups or teas often help to loosen them up.
Asked whether it was better to cough up the phlegm and spit it out (into a tissue, of course) or swallow it, Marshall replied it truly didn't matter.
"It's more an issue of personal preference," he said.
Cold & Flu season is here! Visit the ABCNews.com OnCall+ Cold & Flu Center to get all your questions answered about these nasty viruses.