It starts when greasy secretions from the skin's sebaceous glands (oil glands) plug the tiny openings for hair follicles (plugged pores). If the openings are large, the clogs take the form of blackheads: small, flat spots with dark centers. If the openings stay small, the clogs take the form of whiteheads: small, flesh-colored bumps. Both types of plugged pores can develop into swollen, tender inflammations or pimples or deeper lumps or nodules. Nodules associated with severe cases of acne (cystic acne) are firm swellings below the skin's surface that become inflamed, tender, and sometimes infected.
Although acne remains largely a curse of adolescence, about 20% of all cases occur in adults. Acne commonly starts during puberty between the ages of 10 and 13 and tends to be worse in people with oily skin. Teenage acne usually lasts for five to 10 years, normally going away during the early 20s. It occurs in both sexes, although teenage boys tend to have the most severe cases. Women are more likely than men to have mild to moderate forms into their 30s and beyond.
Hope this helps⬆️
My mums a dermatologist so I know this sort of stuff