Each morning when we wake up, and every evening, when we retire, it has been noted that we often accumulate small amounts of lint, or 'fluff', in our navels¹. Commonly referred to as 'belly-button fluff', the exact nature and cause of its appearance has been a mystery for generations. Thankfully, recent experiments in Australia may have found the answer at last.

So, What is Belly-Button Fluff?

Quite simply, it is collected fibres from your clothing. There's probably a little dead skin in there too, but the majority of it is small fibres from your clothes. Contrary to popular belief, evidence suggests that belly-button fluff comes up from underwear rather than down from your t-shirt or top.

We all have body hair to some degree. Women tend to have fine, almost invisible body hair, while men's hair is coarser and more visible. The hair drags fibre residue up from the 'pants' area until it congregates in the navel.

Karl Kruszelnicki, a physicist at the University of Sydney, Australia, conducted a major study² of this strange occurrence over the space of a year. Just under 5000 participants answered his survey from across Australia and elsewhere, and over 66% admitted to experiencing fluffage in the naval region.

One theory suggested that hairier, overweight people are more likely to produce fluff, so some of the participants were asked to shave their stomachs to see how this affected the results. Though the findings were inconclusive, Dr Kruszelnicki did find that a large proportion of the shaved subjects noticed a decrease in the amount of fluff production, presumably because there were no hairs to carry the fluff over the curve of the bellies. However, some of the slim, hairless, female participants also confessed to experiencing fluff build-up. Kruszelnicki deduced that this might be down to certain bodily movement that continues to move the fluff into their belly buttons without the involvement of body hair.

But Why is It Always Blue?

It has been observed that belly-button fluff tends to be of a blueish tint. Sometimes it looks a little grey, sometimes purple, but generally it's a pale blue colour. Most clothing has elements of blue or white. The dyes in black clothing, for example, are often not actually black but a very dark blue.

If you have a clothes dryer, have a look at the lint filter - that tends to be blue too.

Random Facts

• Belly-button fluff makes great kindling for fires.

• Belly-buttons are as unique as finger-prints. But belly-button prints would probably be impractical.

• Pierced navels tend not to collect fluff, probably because they tend to be exposed and therefore less likely to collect all those tiny fibres.

Further Fluff-related Reading

• See close-up pictures of belly-button fluff courtesy of the University of Sydney's electron microscope.

• One man's fluff obsession taken to disturbing levels

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¹ The indentation in human abdomens that appears at childbirth after the umbilical chord is severed and tied up. Some people have navels that are quite deep - known as 'innies' - others are either shallow or convex - known as 'outies'.
² 58.1% of participants were male, 41.9% female