Mucus may be gross, but without it, we would all be much more prone to respiratory infections. Mucus is produced along the entire respiratory tract: the nose, sinuses, throat, trachea and lungs. It forms a protective barrier to trap airborne particles.

Every hour, an adult human breathes in about 250 liters of air. In the air are particles such as dust, pollen, smoke, bacteria and viruses. The body's first line of defense against these particles is nose hair, which filters out some of the larger particles.

For those of you without a lot of nose hair - or if you breathe in through your mouth - many airborne particles will reach your sinuses, throat, trachea and lungs. Your mucus then traps the particles.

Tiny, hair-like projections line the respiratory tract and constantly move mucus to the back of the throat, where we swallow it (though some folks prefer to spit out this mucus.)

We each produce and swallow close to a liter of mucus each day. Any potentially harmful bacteria or virus we have inhaled and then swallowed passes through the gastrointestinal tract without harming us.

People who are allergic to animal dander, dust, pollen or other airborne particles usually produce more mucus than normal. This is how the body attempts to protect itself from these foreign invaders.

Mucus is not a perfect barrier, unfortunately. Viruses and bacteria sometimes get through the mucus to infect the body's tissues, and begin to multiply rapidly. If this happens in the nose, sinuses or throat, it is called an upper respiratory infection (URI). In the trachea or lungs, it is called a lower respiratory infection.

When we are healthy and not suffering from allergies, we usually aren't aware of our mucus. Normal quantities of mucus do the job and don't bother us.

It's only when we are fighting off a respiratory infection or allergies that our mucus production goes up. Then, we produce so much mucus that we need to blow our noses or cough it up to get rid of the excess.

There has been much debate over the meaning of the color of mucus. Traditionally, a lot of clear mucus was thought to be a sign of allergies, white or yellow mucus a sign of a viral infection and green mucus a sign of a bacterial infection. This myth has been disproved.

The color of mucus has more to do with how long it has been in your body before it is expelled. Mucus is clear when it is produced, but becomes white, yellow, green or brown as time goes on and gathers up particles and cellular debris. When you blow your nose in the morning, that mucus is generally darker (since it's been sitting in your nose and sinuses all night) than mucus you blow out later in the day.

The color of your mucus alone won't tell you what type of infection or allergy you have. But, it can be helpful when considered along with your other symptoms. Sneezing and itchy eyes usually indicate allergies. A fever and fatigue along with too much mucus indicate a viral or bacterial infection. Coughing up a lot of mucus and feeling short of breath indicate a lung infection (bronchitis or pneumonia).

Mucus is constantly produced, so it needs to constantly be swallowed, coughed up or blown out. When mucus accumulates in the nose, sinus, back of the throat or the lungs, we feel uncomfortable due to pressure.

It's important to keep mucus moving. Drinking plenty of fluids, breathing in steam and taking an expectorant or decongestant can help excess mucus drain. Blow your nose gently when you need to; blowing your nose too vigorously can force mucus back into your sinuses and increase the likelihood of an infection.

Kathryn B. Brown is a family nurse practitioner with a master's degree in nursing from OHSU. Is there a health topic you would like to read about? Send ideas to


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