Asked by: Geoff Graves, Manchester
Navel lint, or belly button fluff, is mostly made from your underwear. The majority of clothing fibres just contribute to house dust, but underwear fibres get caught by the hairs below your belly button, which points upward and towards your mid-line. As your underclothes rub against your skin, the fluff ratchets its way up to your navel. Men get more fluff because they have more body hair.
Get more fascinating Q&As from BBC Focus magazine by following @sciencefocusQA