Mucus

What is mucus?

Mucus is a slippery fluid that lines your respiratory, digestive, urinary and reproductive tracts. It acts like a shield to keep out harmful germs (pathogens) while also letting in things your body needs, like oxygen and nutrients. It also lubricates and moisturizes organs and structures in your body.

You might know mucus by one of its other names, like snot, phlegm or sputum. And you probably only think about it when you’re trying to get rid of it — like when there’s far too much mucus dripping from your nose or clogging your throat. But mucus is an important part of your immune system that’s constantly putting itself in harm’s way to keep you safe. 

What does mucus do?

Mucus has a lot of important jobs, including:

• Blocking germs and harmful particles from getting into your body’s tissues.
• Housing antibodies to disable and mark germs for destruction by immune cells.
• Trapping things that could harm you and moving them out of your body.
• Moisturizing your mucous membranes (mucosa) — the parts of your body that open to the outside world.
• Lubricating your mucous membranes. This helps different parts of your body perform different functions. For instance, it helps food move through your digestive tract and provides a way for sperm to get to an egg for fertilization in your reproductive tract (cervical mucus).

Where does mucus come from?

Goblet cells — specialized epithelial cells that are shaped a bit like a fancy drinking glass — and other cells in your mucosa create mucin, the main component of mucus. Mucus lines your:

• Sensory organs — your eyes, ears, mouth and nose.
• Respiratory system.
• Digestive system.
• Urinary system.
• Female reproductive system.
• Male reproductive system.

What’s in mucus?

The “ingredients” that make up mucus give it its consistency and help protect you from germs. They include:

• Water.
• Electrolytes.
• Enzymes.
• Antibodies (immunoglobulins).
• White blood cells.
• Mucin, a type of protein that gives mucus its gel-like consistency.

What does mucus look like?

Mucus is usually clear, thin and slippery. If you have a respiratory or sinus infection, the mucus coming out of your nose or throat may be thick, sticky and creamy white. Dead cells, germs, tobacco smoke and other substances in your mucus can change its color. Mucus colors include:

• White, cream-colored or light yellow. When your mucus gets dense and appears white or creamy, it usually means you’re fighting a cold or other viral infection. The color and thickness come from immune cells fighting the infection.
• Bright yellow or green. This also is usually a sign of infection. Based on your other symptoms and how long they’ve gone on, it could mean you have sinusitis, or a bacterial infection in your sinuses.
• Red or pink. Blood can make your mucus pink-tinged or streak it with red. You might have blood in your mucus if your nose is dried out or irritated. Small blood vessels in your nose can burst and leak blood.
• Brown. Air pollution or smoking can cause brown mucus. It also could be a sign of infection.
• Black. This can be something you inhaled, but it can also be a sign of a serious fungal infection.

Mucus color alone won’t tell you if you have a specific kind of infection. See a healthcare provider if you have dark-colored mucus — or any other color that concerns you — especially if you have other symptoms, like facial pain or headaches.

What color mucus is healthy?

When you’re not sick, mucus is usually clear. Thick mucus that appears creamy, yellow or green could mean you have an infection. You might get a runny nose with large amounts of clear mucus if you have allergies.

What conditions affect mucus?

Anything that causes inflammation or activates your immune system can change the amount, color or consistency of mucus in different parts of your body. Hormones and genetic conditions can also affect it. Conditions that affect your mucus include:

• Infections. Being sick with sinusitis or respiratory infections is the most common cause of excess amounts of thick mucus in your nose or throat. 
• Allergies or irritants. Allergies and other irritants in your respiratory tract can cause excess clear mucus. 
• Lung diseases. Damage to your lungs and airways from bronchiectasis, COPD (chronic obstructive pulmonary disease) and other chronic lung diseases can cause mucus buildup.
• Cystic fibrosis. CF is a genetic disease that creates thick, sticky mucus that gets stuck in your pancreas and lungs.
• Digestive issues. Diverticulitis, inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) and anything that irritates your digestive tract can cause mucus in your poop (stool).
• Hormone issues. Menopause and conditions that cause low estrogen decrease the amount of mucus in your reproductive tract, which reduces fertility and causes vaginal dryness.
• Cancer. Certain types of cancer can arise from mucin, like mucinous carcinomas.

How do I get rid of mucus?

Most of the time, excess mucus is something you have to deal with when you’re sick, while your body tries to clear out germs and dead immune cells. Some treatments that can help with mucus include:

• Expectorants. Expectorants can thin out thick mucus and help you clear it out of your chest.
• Nasal rinses. These can help break up and clear mucus from your nose and sinuses. Make sure you follow precautions to use them safely.
• Decongestants. Decongestant medications or sprays can temporarily reduce the inflammation and mucus in your nose and throat.
• Antihistamines. These can prevent or calm down allergic reactions that cause too much mucus.
• Mucolytics. Mucolytics treat chronic lung diseases like cystic fibrosis.

When should I see a healthcare provider?

See a healthcare provider if you have mucus that’s an unusual color (like bright yellow or green), is very dark or has a lot of blood in it. They can determine whether you have an infection that needs treatment.

What’s the difference between phlegm and mucus?

Phlegm is a type of mucus that you usually cough up from your lower respiratory tract. It’s typically thicker than normal mucus because it’s helping fight an infection.

Should you swallow phlegm or spit it out?

If you cough up phlegm into your mouth, it won’t hurt you to swallow it. Some people find that this makes them cough or it feels like it gets stuck in their throat. Or, it just feels gross. In that case, it’s perfectly OK to spit out phlegm — as long as you’re being considerate of other people while doing it.

If you can, find a tissue or napkin so you can spit your mucus into it and throw it away. Then, be sure to wash your hands. If you don’t have a tissue, step away from others before spitting.