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Medical Minutes: Answers to frequently asked questions


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Kristin Schiller


Question: What is mucus?

Made up of water, proteins and salts, mucus helps keep underlying tissues from drying out. It is also our first line of defense against foreign particles (including dust, allergens, viruses, and bacteria). When we breathe in, these foreign particles get trapped in the mucus lining our respiratory tract.

We don’t really think about mucus until we get sick and suddenly it’s everywhere. Mucus producing tissues line our respiratory and digestive tracts (nose, mouth, sinuses, throat, lungs, stomach and intestines). The average healthy person produces between 1 to 1.5 liters of mucus a day. Normally mucus is thin and watery. When we are fighting an infection, the amount and consistency of mucus can change.

My mucus is green. Does that mean I have an infection?

You cannot tell the difference between a viral or bacterial infection based on mucus color alone. Having green mucus does not mean you need to be on an antibiotic. Remember, yellow and green mucus means your immune system is doing its job. A complete history and physical exam will help your provider decide if antibiotics are indicated or not. Antibiotics do not treat viral infections. Extra fluids, honey, anti-histamines, decongestants and expectorants can all help treat excess mucus when you are sick.

Can you explain how mucus changes?

Our immune system sends white blood cells to help combat these trapped foreign invaders. Enzymes or chemicals in our white blood cells break down the trapped materials. When the products of this breakdown process are exposed to oxygen they oxidize and turn color - just like rust.

When our respiratory tract becomes inflamed, the passage of mucus is slowed. Normally clear and watery mucus becomes concentrated and turns thick and white. When our white blood cells get to work breaking down foreign materials, mucus can change color to bright yellow or green. This color change means your immune system working. Brown mucus is usually from dried red blood cells from inflamed and irritated nasal and sinus passageways.

What are best practices to avoid getting sick?

To avoid getting sick in the first place, practice good infection control hygiene. Wash your hands often and avoid touching your face.

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