Dr Steinhauser made his discovery after studying 503 pieces of fluff from his own belly button. Chemical analysis revealed the pieces of fluff were not made up of only cotton from clothing. Wrapped up in the lint were also flecks of dead skin, fat, sweat and dust. Some people have belly buttons devoid of fluff while others must clean lint out of theirs every day.
It depends on what style of belly button you have. Bulbous belly buttons usually stay fluff free but indented types can end up with enough fibre to knit a scarf. It is also a matter of Physics says a Dermatologist.
The belly button fluff is formed due to excess heat and humidity from the hole that traps a mixture of water, dust, clothing fibre, etc. The reason for the colour of fluff to be blue is yet to find.