Once you understand how acne forms, you will be in control of your own skin. (Please note that this is my understanding only for non-hormonal acne based on articles I've previously read since my college days.)
I will try to make this as simple as possible with only the important parts.
Acne starts from the combination of a hair follicle, hair, and a sebaceous gland that produces sebum (which is all in a pore), a little moisturizing friend that can become an enemy real fast when it loses control and mixes with other particles and bacteria. Sebum fills up the hair follicle (think of the hair follicle as the flower stem standing straight up in a Corona beer bottle). The sebum fills up the space around the flower stem that is standing up straight. When this space gets completely filled it overflows to the surface of the skin (for this beer metaphor, the flowers and buds are affected), giving you a healthy glowing look (a feature of normal skin types that doesn't require as much pore maintenance). If your skin is well hydrated (hello, hydrating essences, toners, emulsions, face masks, and everything hydrating!), then your sebaceous glands don't need to work so hard to moisturize your skin.
Skin sheds from the inside out. New skin cells contain a nucleus that flattens over time and eventually disappears as the skin cell travels through multiple skin layers to the surface of the skin. Dead skin cells contain no nucleus and are ready to fall off the skin (exfoliators, happy hi!!). For this, just imagine layers of marbles. New skin cells are the perfectly round marbles and dead skin cells are the flat marbles that sit at the bottom of many fish tanks. The flat marbles rest on the round marbles.
As dead skin cells shed and sift to the surface of the skin, they become more sticky as they are mixed with the sebum that is already in the hair follicle. At this point, the pore becomes clogged, but we don't know that (welcome, exfoliators and oil cleansers)! It still looks normal from the outside because the changes are all inside the pore. However, now, the dead skin cells and sebum cannot escape the pore. P. acnes, a common bacteria that sits in the pore, loves sebum. It eats sebum and thrives. During this stage, the bacteria is contained in the pore, so it does not affect the surface of the skin (shows that when you control sebum, you can thus control the activity of the bacteria that lives in your pores).
Corneocytes (a mixture of sebum and loose dead skin cells) contribute to whiteheads and blackheads, which are a buildup of thick corneocytes (pore strips and packs, huge hi!). Whiteheads happen when the pore is narrow or closed. This is also called a closed comedone. Blackheads happen when the pore is open and is exposed to oxygen. This is called an open comedone.
Blackheads and whiteheads can become infected if the bacteria is able to spread to the surrounding cells right next to the pore that is clogged. When corneocytes build up and apply too much pressure to the pore, the pore breaks and the infected mixture of bacteria and sebum spreads to the nearby skin areas (if we continue with the beer metaphor - if the beer bottle is sitting on a table, think of the table as the surrounding skin, although the table would ideally be at the same level of the opening of the bottle), which causes pimples. A pimple begins as a red bump first, and after white blood cells have killed off the bacteria in the pore, that yucky white pus forms, which is the remaining dead white skin cells and a major tempter of those who like to pop them (please use an extractor and not your fingers!). If the mixture of bacteria and sebum infect the skin deeper, crater scars form, which require more than just cleaning - now the skin needs to be repaired (snail extract, hi!).
Do you now have a better understanding of how acne develops? Maybe because I have a background in science, I am a person who needs to know the whys and understand what is going on with everything before I can do a good job. Because I truly care about skin and think that is is a main focal point for beauty, I read into this stuff a lot. Once I know, I act on it and use my products with a strategy in mind. I always strive to prevent problems from happening, so I make sure that my pores are clean by stabilizing the hydration level of my skin. When I see that I have a red bump, I know that it means I've been slacking in keeping my face clean and hydrated. I let my skin talk to me, and I act accordingly. Once I act accordingly and understand what my skin needs, I learn how to prevent, prevent, prevent, and prevent even further. I like to ignore the suggested doses and "times a week" that packaging tells me. If I have a lot of whiteheads one week, I use the nose strip 4 times a week. I make sure to think about my skin and my skin only, and I cater to my skin and my skin only when using products. Micro-diagnosing, see?
I hope I got you to think about your skin more in a logical and scientific manner! Skincare is all about science as so much R&D is required to make quality skincare products that truly work. If anything is unclear or you have any questions, please leave me a comment and let me know! I try my best to respond as quickly as possible because as I've mentioned before, your skin is aging every minute! Don't put off taking care of your skin! :)