system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some zits have solid cores, and others just have puss like liquid?
gpt
A zit that's full of pus is an active infection in your skin. It's probably also red and tender to the touch. 

A zit that has a solid core is just a clogged pore. It might be raised and red, but it probably isn't tender or painful.

EDIT: Now what was that extra S doing there?