Once inflammation begins in the skin, it triggers a process called hyperkeratinization, which occurs when the skin produces too many skin cells (keratinocytes) and too much protein (keratin). This causes the pore to narrow and clog initially, forming the very first type of clogged pore in acne, called a microcomedone.5

When a pore is clogged, skin oil, called sebum, begins to build up inside of it. When there is a large enough buildup, it becomes visible to the naked eye. At this point, the acne lesion is called a comedone, more commonly known as a whitehead or blackhead.

A lot of this is stuff I picked up over a decade of dealing with chronic and painful acne, so I'd probably have to spend an evening finding different articles lol

But, yeah, acne comes from inside. It's a more like an allergic reaction, where a normally helpful part of the immune system freaks the f out and causes harm. The bacteria that sometimes causes acne also comes from the body and normally lives harmlessly in our skin oil. And it's not even always the cause! Sometimes bacteria doesn't grow inside the zit at all, though it usually does and when it does it usually makes it a lot worse.

Gosh there's just so much stuff. Scrubbing with a cloth or using overly hot water actually make acne worse because they cause irritation, which triggers a stress response. Overly drying soaps can cause acne by drying out the skin, which can trigger a stress response. Sunlight is necessary for human life, but lots of exposure causes inflammation and stress.

Acne.org has a lot of good info, highly recommend.