# What causes sputum/phlegm/runny noses when sick?

**URL:** <https://boards.straightdope.com/t/what-causes-sputum-phlegm-runny-noses-when-sick/231038>\
**Category:** Factual Questions\
**Created:** [February 25, 2004, 4:04am UTC](https://boards.straightdope.com/t/what-causes-sputum-phlegm-runny-noses-when-sick/231038 "2004-02-25T04:04:06Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\
**Post date:** [February 25, 2004, 4:04am UTC](https://boards.straightdope.com/t/what-causes-sputum-phlegm-runny-noses-when-sick/231038/1 "2004-02-25T04:04:06Z")

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Why do we cough and have a runny nose when sick? I have several theories, and I hate to answer my own GQ but I have no definitive answer and would like to know the exact cause.

-it is a result of histamine (if so, how/why?).  
-it is a byproduct of our immune system attacking an infection (how/why?).  
-The virus/bacteria disrupt the cilia and surfactant layer in the lungs, which we must eject in the form of sputum.  
-our nose/lungs increase the rate at which they produce mucus to prevent bacteria/viruses from settling down too easily.  
-we cough to clear the airway of debri that isn’t being swept out due to cilia disruption.

Does anyone know which of the above are correct or know of additional causes?

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**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\
**Post date:** [February 25, 2004, 5:56am UTC](https://boards.straightdope.com/t/what-causes-sputum-phlegm-runny-noses-when-sick/231038/2 "2004-02-25T05:56:55Z")

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I’m not sure this is the definitive answer, but I’ll give it a shot. Infection and inflammation usually go hand-in-hand. Inflammation is the host response to tissue damage of nearly any cause. Leaky, dilated blood vessels typify inflammatory states. Fluid and immune cells transit from within the vessels to epithelial surfaces (ie nasal or airway mucosae). The excess fluid accumulation causes the runny nose. My bet is that mucus production is stepped up as well as part of the inflammatory response.

I think Cecil did a column about how much nose juice is lost during the average cold. I’ll look for it and be back in a sec.

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**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\
**Post date:** [February 25, 2004, 5:59am UTC](https://boards.straightdope.com/t/what-causes-sputum-phlegm-runny-noses-when-sick/231038/3 "2004-02-25T05:59:52Z")

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[The Master speaks.](http://www.straightdope.com/classics/a971017.html)

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**Author:** ![Bob55](https://avatars.discourse-cdn.com/v4/letter/b/e9c0ed/32.png) [@Bob55](https://boards.straightdope.com/u/Bob55)\
**Post date:** [February 25, 2004, 7:26am UTC](https://boards.straightdope.com/t/what-causes-sputum-phlegm-runny-noses-when-sick/231038/4 "2004-02-25T07:26:28Z")

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Thanks for the link, it was very informative. It does address nasal mucous but ignores lung phlegm though, but your answer goes into that somewhat. Maybe it is inflammation combined with cilia damage.