system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do the blades of a rotating fan collect dust over time? If its spinning, shouldn't all the dust be just 'blown away'?

I'm talking about ceiling fans / pedestal fans. I have one at home, and every few months it needs cleaning because of the thick layer of dust that sticks to the blades / propellers. How does it get there, and why doesn't it get blown away when the fan is turned on?
gpt
A lot of airborne particles are skin cells which have oil on them so once they land they they stick and make it easier for other things to stick.  There are other airborne particles of oil from cooking, exhaust, etc that add to the problem.