Modeling the production of belly button lint

We show that respiratory cycle provides a periodic traction force for the production of belly button lint or navel fluff. The relative motion induced between clothing and skin, during breathing, transports the clothing fibers over the abdominal skin via an asymmetric sliding mechanism effected by the specific orientation of the cuticle scales of body hair. The source of these fibers can be the piece of clothing worn adjacent the navel area or the drying towel used after shower. The ratchet like topology of hair surface ensures a net unidirectional transport of these fibers. Since the predominant direction of growth of hair in the abdomen is toward the navel, this unidirectional transport leads to a perpetual accumulation of fibers in the navel over the course of the day. By analyzing the force balance on a moving fiber and the transport dynamics of its number density distribution, we develop a mathematical model to describe the accretion rate of lint fibers in the navel.