system
Given the following post, respond as if you're commenting on Reddit:
human
What is the white stuff inside pimples? What it's made out of, why we have it, and why does it exit in this way?
gpt
A pimple is an infection. Bacterial infections begin with a bacterial pathogen and an inflammatory response to the pathogen. For pimples, anaerobic bacteria colonize a hair follicle and consume the sebum produced by sebaceous glands. This forms lipid byproducts which irritate the surrounding area. This inflammatory reaction recruits immune cells called neutrophils (a type of WBC). Neutrophils come in and dump bleach on the bacteria. As neutrophils die, they accumulate and form what we call pus or the “white stuff”. It only has one immediate way out; through the hair follicle to the skin surface. That’s why it exits that way. 

Edit: correction about sebaceous glands (not sweat glands)

Edit2: I’m getting a lot of questions about the one way out. Added that exit to the skin surface is the only immediate way out. After a few days the pimple will resolve following absorption back into the body.