Why are boogers sticky?

★ wanayoo — archive 1999 http://www.howstuffworks.com/question81.htm

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Each weekday Marshall Brain answers questions submitted by the readers of How Stuff Works in the Question of the Day section of HSW. You can also view previously answered questions in the HSW Question Archive. Here is today's question!

Question

My four year old asked, "Why are boogers sticky?" I really didn't know what to say...

Answer

No doubt your child is just starting a brilliant scientific career with this question!

"Boogers" are made of mucus. Mucus is made by mucus membranes. Your body has mucus membranes in all sorts of places: the stomach, intestines, nose, lungs, eyes, mouth, and the urinary tract all contain mucus membranes that secrete mucus.

Mucus contains mostly water and mucin (during a sinus or lung infection it also contains dead white blood cells that have been working on the infection - see the HSW article on the immune system for details). It is the mucin that makes it sticky.

Mucin is a branched polysaccharide. If you have read the HSW article entitled How Food Works you learned about saccharides - they are sugar chains. Starch, for example, is a polysaccharide. As you know, if you mix corn starch or flour with water, you get a sticky substance - mucin is doing the same thing. Mucus is essentially a thin paste made of mucin and water.

Show your four year old how corn starch and water (especially as it dries out) is sticky and he will be looking at synthetic boogers!

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