Friday Weird Science: All you ever wanted to know about belly button lint

Mar 27 2009 Published by under Friday Weird Science

First of all, Sci loves the journal of Medical Hypotheses. Where would I BE without that journal? In a much less entertaining place is where I'd be.
Secondly, Sci loves the phrase "belly button lint". I'm not really sure why. I think it's because the phrase "belly button" is humorous regardless, and then adding the "lint" just...makes it funnier.
Finally, I love this study. Aside from being about belly button lint, and therefore hilarious, I think this study emphasizes how curious scientists are. many ways. We get hold of a question, and we just can't let it go! Often, that question is something like "why do pancreatic beta cells in the Islets of Langerhans self-destruct in type I diabetes, but alpha cells are left unharmed?", or "what are the mechanisms in the brain which bring about the symptoms of depression?" But sometimes, those questions are "why do some people have SO MUCH belly button lint?" Steinhauser, G. "The nature of navel fluff" Medical Hypotheses, 2009.

So according to Chemical and Engineering News (Sci reads every issue like a good little neurochemist), this project came about because the author's wife wanted to know about belly button lint. She apparently got a LOT more than she bargained for. The researcher got his teeth into the question, scientist-style.
What is belly button lint? And why do some people get a ton of it, and others don't? Belly button lint, or "naval fluff", is commonly composed of lint from your shirt or other clothing article, combined with other things such as dust, which is deposited in your navel. Interestingly, the author reported that men suffer from far more naval fluff than women. Why could this be? The author of the study hypothesized that increased naval fluff collection in men was primarily due to augmented body hair in the abdominal region. Guys are hairier, so they have more fluff. This would also mean that hairer men would collect more naval fluff than non hairy men
How would abdominal hair increase naval fluff collection? Dr. Steinhauser thinks that hair, with it's curls and scaly structure, would be more likely to abrade your shirt than smooth skin would. This tiny about of friction would rub small fibers off your shirt. Naval hairs tend to curl in toward the belly button and often grow in concentric circles around it, and so the fibers would naturally begin to collect in the depression. People without hair on their bellies would have less abrasion, and less direction in toward the belly button.

This researcher went one step further than most who submit to Medical Hypotheses. He collected preliminary data. THREE YEARS WORTH. Since March 2005, he has collected 503 pieces of naval fluff (one wonders where he stored it and what people thought when they saw it). The total weight of all fluff collected together was almost 1g! Average weight, however, was more like 1.8 mg, though the median was around 1.2-1.29, there were a couple of big collections (as much as 9 mg!) that skewed the data. He observed that the heaviest fluff days were those on which he wore brand new or extra soft t-shirts, while older shirts and dress shirts resulted in less lint.
Observations showed that the fluff tended to resemble the shirt that the author was wearing that day. The author of this study, who is, in normal life, a chemist, decided to analyze the fluff contents, using lint obtained on days when he wore white shirts. The white shirt would yield lint that was closest to just cellulose, which would make other impurities coming from the environment easier to detect. He found that, though there wasn't much difference from cellulose, (very similar values of cabon, nitrogen, and hydrogen were obtained), he also found solid nitrogen and sulfur compounds in the fluff. This could be the result of contamination from dust in the air, but also from things like your sweat. This led him to hypothesize that belly button lint actually helps keep your belly button CLEAN by trapping nasty stuff that would otherwise get stuck there.
So was it the presence of abdominal hair that caused the lint to accumulate? Here the author showed his real dedication to science. He shaved his belly. He then observed a drastic decrease in belly button lint collection, which increased only after the hair grew back.
So what did he conclude?
1) Belly hair increases belly lint
2) If you don't want belly lint, wear old shirts or dress shirts that don't have a lot of lint
3) Average mass of naval fluff was 1.82 mg
4) If you take the lint by weight resulting from an average tshirt, and multiply it over the times a tshirt can be worn over a year, it's possible that your shirt could lose 182 mg of fiber from lint collection alone!
5) Your lint in contaminated with stuff from you and stuff from the environment. Does this help keep your belly button clean by trapping contaminents?
I think this study is hilarious, and I really admire this scientist's dedication to his field. I wonder...perhaps we could help him collect some additional data? Maybe a survey? But it will have to wait for tomorrow. For now, Sci needs to go to bed. But she might check her belly button for lint before she goes.
Steinhauser, G. (2009). The nature of navel fluff Medical Hypotheses DOI: 10.1016/j.mehy.2009.01.015

7 responses so far

  • photon says:

    Unfortunately for Dr Steinhauser, the IgNobel Prize in this area has already gone to Dr Karl Kruszelnicki of the University of Sydney in 2002, for his ground-breaking survey of factors affecting bellybutton lint.

  • Larry Ayers says:

    I risk charges of indelicacy, but I'll offer an alternative or additional hypothesis. As Alfred Kinsey documented decades ago, masturbation is very common amongst even married men. Often the ejected semen pools in the navel and is wiped up with tissues, etc. I'm reasonably certain that a thin and sticky film remains, even after assiduous wiping. Lint, I surmise, tends to cling to this film like cockleburs to a dog's coat.
    Great post! I enjoy reading analyses of those under-reported mundane details of our lives.

  • Haha - I was going to write an indignant comment that Steinhauser had been preceded by the Awesome Dr Karl but it looks like photon beat me to it!

  • And Larry beat me to the other potential hypothesis 😉

  • Alex says:

    I don't think the alternate hypothesis just proposed is right. As I am at work I'll avoid going into too much detail.
    In my experience avoiding the situation Larry described, either by refraining from the behaviour in question or via other methods of fluid control, results in the same amount of lint as in the situation described. However there is a definite effect on lint quality.

  • JR Minkel says:

    @Larry Ayers - wow - did you really say "cockleburs"?

  • Alyssa says:

    I never get belly button lint since I don't have hair on my stomach. so ya. there is one more number to your survey ^_^

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