system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does our face, especially the nose and forehead get oily but other body parts like your knees don't?
gpt
Our faces are very porous- little holes from where hair used to be. While cells on our face stopped making hair (at least some of them), some of those oils are still being made; the oil isn't soaked up- and there is a lot more being made compared to our knees.
 

Also the sun stimulates production of these oils. 

On a cellular level: differences in how the cells are 'wired' - what their job is.