system
Given the following post, respond as if you're commenting on Reddit:
human
Do astronauts need to clean the outside of space station windows?
gpt
There's not enough "stuff" in space to dirty the windows of the ISS naturally. However, departing and  incoming shuttle thrusters give off enough particulate to dirty the windows over time. Back in 2015, the Russians on the ISS did an EVA to clean the windows.

So yes, but very slowly.