Why your belly has a built-in lint trap
After a long hard day of moving, sweating, and shirt-wearing, many people can enjoy a brief ritual of removing a tuft of lint from their belly buttons. Known in research circles as “navel fluff,” this common occurrence has been ignored or taken for granted by “outies,” who can’t really partake in belly-button cleaning, or curious researchers like Dr. Karl Kruszelnicki and Georg Steinhasuer. While nothing about this lint is likely to reshape your world, it’s never bad to understand what’s happening just under your nose, and above your waistline.
Belly button lint is primarily composed of stray fibers from your clothing. Throughout the day, an innie belly button can act a bit like the lint-trap on a clothes dryer. Different conditions can affect just how much lint you can gather in a day, with the optimal conditions including having a pudgier, hairier tummy and a new t-shirt with more loose fibers to collect. Tests have included matching shirt fibers to lint at the end of the day, as well as more drastic measures like having volunteers shave the hair off their stomachs.
Hair matters because each hair around your belly button may actually act like a one-way guide trapping lint into your navel. The tiny scales along the shaft of each hair point towards the tip, and catch fibers from the lint, stopping them from moving back out towards the rest of your abdomen and being dispersed.
Shirt fibers aren’t the only thing being caught in belly buttons of course. Other common materials include sweat, dead skin, and of course lots of benign bacteria. Belly buttons seem to actually be a fertile environment for bacteria, as among only 60 samples over 2,368 species of bacteria were discovered. For reference, that’s more distinct species in your belly scar than there are birds or ants in North America. If you’d like to remove some of this ecosystem for any reason, you should have a convenient cotton swab available at the end of the day— just remember to wear a new t-shirt.
Source: The curious truth about belly button fluff by Jason G. Goldman, BBC Future