What Is Mucus? 9 Questions You've Always Wondered About Snot and Phlegm

Mucus is made of mostly water, which gives it its liquid texture. But it also contains proteins and salt. Sugar-containing proteins (or glycoproteins) specifically, called mucins, give mucus its gelatinous consistency. Discarded infection-fighting white blood cells plus other debris picked up in the nasal passageways often catch a ride in the mucus too. Also, fun fact: Boogers are just dried up mucus mixed with other particles like dirt, dust, and pollen.

Where Does Mucus Come From?

Your body is a mucus-making machine. Special cells and glands found in the thin lining (called the mucosa or mucous membrane) of body cavities and passageways leading out of the body regularly produce the slippery stuff.

You probably already know that mucus-secreting tissue can be found in the nose, mouth, throat, and lungs. But it's also in our eyes, ears, GI tract, and reproductive and urinary organs.

Why Do We Make Mucus?

Think of mucus in the respiratory system as "a film that protects the important parts of the inner nose and lungs," says allergist and internist Tania Elliott, MD, chief medical officer at EHE, a New York City-based healthcare company specializing in preventive medicine. It keeps nasal passages (and lungs) well moisturized. "We don't want those things dried out!" she says.

When a cold virus enters your nose, mucus production goes into overdrive, Dr. Welch explains. "It's a reaction of the body against viruses, bacteria, or even particles of dust," he says. It prevents those irritants from burrowing deeper into the lungs. Then, the tiny hairs in the respiratory tract called cilia help to sweep up the infected mucus like little brooms, says Dr. Elliott, so we can cough or blow it out.

Why Does Mucus Get Thicker When We're Sick?

Sometimes mucus gets thicker when we're fighting off an infection. But it can also be thin and runny. It all depends on the type of virus or irritant activating the body's mucus-producing tissues, explains Chandra Ivey, MD, a private-practice laryngologist and assistant clinical professor at the Icahn School of Medicine at Mount Sinai in New York City.

Smokers, for example, tend to have more mucus and thicker mucus, she says. In the case of a cold, a thicker wall of mucus can serve as a barrier preventing other viruses, bacteria, or irritating particles from entering the nasal membranes, she says.

Mucus can also get thicker if you're taking certain medications that dehydrate your body, she adds. That's another good reason to get extra liquids when you're sick.

Why Does Mucus Make It Hard To Breathe?

Stuffy nose? It's usually the swollen mucosa–the mucus-generating tissue that lines your nose–that's blocking your nasal passageways, not the mucus itself, Dr. Ivey says.

Other times, mucus can get thick like sludge, blocking the sinus cavities and preventing proper drainage, adds Dr. Elliott. "This leads to increased pain and pressure."

What Does a Change in the Color of Mucus Mean?

Mucus is generally clear. If you have a cold, it can turn white or even yellow (especially if you're dehydrated). A greenish hue may signal the presence of a greater number of infection-fighting white blood cells. But doctors say color alone isn't a great indicator of a bacterial infection.

"It can turn yellow or green even with a virus," notes Dr. Welch, who cautions against rushing to your doctor and begging for antibiotics. The vast majority of colds are viral, not bacterial. Antibiotics don't fight viruses, and their misuse can lead to the development of new strains of bacteria that resist these medicines, he says.

A cold generally runs its course in a week, more or less. If you spike a fever, develop a cough, or have other signs that your condition is worsening, that's when it's time to call your doctor.

Do Antihistamines or Decongestants Help Relieve Mucus?

These medicines are available over the counter in the form of pills, liquids, and nasal sprays. And while they may help ease cold symptoms, using them too often can make them less effective over time.

Antihistamines block inflammation, so there's less tissue swelling and, in theory, less mucus production, Dr. Ivey says. Decongestants improve your breathing by constricting blood vessels in the area.

Does Drinking Extra Fluids Help Mucus?

Mom was right: You should feed your cold with plenty of liquids. Staying well hydrated can help thin out mucus so that it's easier to expel.

But a lot of cough and cold medicines can be very drying, Dr. Elliott says. What's more, when you're sick and don't feel like eating, your water intake naturally decreases. If you have a fever, you're also losing fluid by sweating. Replenishing fluids is key, she says, to feeling better.

How Else Can You Get Rid of Excess Mucus?

Honey is a good mucus thinner, Dr. Ivey says. If you're coughing up phlegm, try stirring some honey into a mug of tea. "It wraps around the little particles in the mucus and helps your body clear it," she says.

Using a nasal irrigation device, like a neti pot, can help move mucus out of your nasal passages. "It washes it through," Dr. Welch says.

As for medications, look for expectorants containing the active ingredient guaifenesin, which can bust up thick mucus, he says.

Dr. Elliott recommends adding eucalyptus to hot water and breathing in the humidified air or eating spicy foods. Both can naturally break up a stuffy nose.