"Hard facts on a soft matter! ... The hypothesis presented herein says that abdominal hair is mainly responsible for the accumulation of navel lint, which, therefore, this is a typically male phenomenon. The abdominal hair collects fibers from cotton shirts and directs them into the navel where they are compacted to a felt-like matter. The most abundant individual mass of a piece of lint was found to be between 1.20 and 1.29 mg (n=503). However, due to several much larger pieces, the average mass was 1.82 mg in this three year study. When the abdominal hair is shaved, no more lint is collected. "

From the materials and methods: "The author first observed the accumulation of navel fluff in his early 20s. Despite thorough body hygiene including a daily morning shower, the navel filled with lint over the day. The author collected 503 pieces of navel fluff since approximately March 2005 with a total weight of almost 1 g... ...In order to investigate the role of the abdominal hair, the author also shaved his belly for this study."

Steinhauser G.

Vienna University of Technology, Atominstitut der Osterreichischen Universitäten, Stadionallee 2, 1020 Vienna, Austria. georg.steinhauser@ati.ac.at

Hard facts on a soft matter! In their popular scientific book (Leyner M, Goldberg B. Why do men have nipples - hundreds of questions you'd only ask a doctor after your third martini. New York: Three Rivers Press; 2005), Leyner and Goldberg raised the question why "some belly buttons collect so much lint". They were, however, not able to come up with a satisfactory answer. The hypothesis presented herein says that abdominal hair is mainly responsible for the accumulation of navel lint, which, therefore, this is a typically male phenomenon. The abdominal hair collects fibers from cotton shirts and directs them into the navel where they are compacted to a felt-like matter. The most abundant individual mass of a piece of lint was found to be between 1.20 and 1.29 mg (n=503). However, due to several much larger pieces, the average mass was 1.82 mg in this three year study. When the abdominal hair is shaved, no more lint is collected. Old T-shirts or dress shirts produce less navel fuzz than brand new T-shirts. Using elemental analysis, it could be shown that cotton lint contains a certain amount of foreign material, supposedly cutaneous scales, fat or proteins. Incidentally, lint might thus fulfill a cleaning function for the navel.