Here’s Why You’re Coughing Up Mucus — And How To Make It Stop

A loose, wet cough is the worst. Hacking up mucus is an unpleasant experience in and of itself — and it sounds pretty gnarly to boot. So you're already sick, and now you have to put up with getting the side eye from anyone who hears you clear your throat.

Even the experts know that phlegm-y coughs are miserable. Case in point: When I called David Cennimo, MD, an infectious disease expert and assistant professor at Rutgers New Jersey Medical School, to talk about mucus, he asked me if I was reporting on this because I “drew the short straw."

But after we started chatting, I discovered that the stuff actually serves a pretty important purpose in the body. Here's everything we know about what makes us hack up mucus, when you should head to the doctor — and how to clear up a wet, rattling cough faster, so you can stop grossing out everyone within earshot.

“Mucus is made of about 95 percent water, with some proteins and lipids, which give it the mucus texture,” Dr. Cennimo explains. It’s secreted all throughout the respiratory system — the mucus you cough up is pretty much the same thing as snot, he says — and it acts like a protective layer, keeping the cells in your respiratory tract from drying out so they can function properly. 

Phlegm also traps the bacteria, virus particles, dust, pollens, and other microbes and debris you may breathe in before they can enter your lungs, where they could lead to inflammation and damage.

“Before they get down into alveoli — the air cells deep in the lungs that allow for the gas exchange into the blood — the microscopic particles get trapped in the mucus,” Dr. Cennimo says. Think of the slick film like the Roomba of your respiratory system.

You're clearing out all that microbe-laden mucus! Microscopic, hair-like bodies on the cells that line our respiratory tract, called cilia, use a wave-like motion to sweep the mucus back out, triggering coughing, Dr. Cennimo says. To stick with the Roomba metaphor, this process is like emptying the vacuum bin when it's full.

The reason you may feel especially bothered by it when you're sick is because you're probably producing more phlegm than usual. On average, we make about 15 milliliters — about half an ounce — of mucus every day, but when you’re sick the body can produce ten times that, Dr. Cennimo says.

It makes sense: When you're ill, your body is being assaulted by more microbes that need trapping. “Inflammation triggers the mucus-producing cells to work harder, so you have more to cough up," Dr. Cennimo explains. Most wet coughs occur when you're sick with illnesses like the flu, bronchitis, or pneumonia, according to Harvard Health. But they can also be from more long-term issues like postnasal drip.

Though you may have heard that green snot is a sign that you're sick, Dr. Cennimo says that medical literature has shown a clear correlation between mucus colour and different health issues.

Even if you're healthy, Dr. Cennimo recommends seeing a doctor if you notice a change in the colour of your regular mucus colour — if it's always been white, then suddenly is green, for instance.

Texture can be informative too. In general, mucus is thicker and stickier when you’re sick, since it contains more immune cells and germs then, and thinner when you’re healthy, reports Medical News Today. (Other factors, including dehydration, can also cause thicker-than-average phlegm.) 

Over-the-counter expectorants, such as Robitussin or my go-to, Mucinex, make it easier to cough up and clear out phlegm by loosening congestion in your chest and throat. You can also try home remedies for quelling the cough, such as swallowing a spoonful of manuka honey or drinking hot tea.

But Dr. Cennimo suggests seeing a doctor any time you start coughing up mucus, since it's a pretty strong indicator that you're sick. And definitely make the visit if the symptoms persist for more than three or so days and they’re hindering your sleep and work life.