"Accordingly, and to the author's personal experience, navel lint seems to be a phenomenon that affects primarily male adults."Now you can say you've already learned something today...
Steinhauser found that hairs around the belly button have a scaly structure that pulls fibers from clothing and then directs those fibers—along with dead skin, fat, sweat and dust—into the belly button.
He wrote that scales on the hair act like "barbed hooks," catching a "melange of foreign materials" and coalescing them into easily removed clumps of lint. Thus, Steinhauser posits, men with abdomen hair likely have "cleaner and more hygienic belly buttons than those who do not"—provided, of course, they go to the trouble of actually removing the lint clumps.