The blocked sebum-filled hair follicle promotes overgrowth of the bacterium Cutibacterium acnes (formerly called Propionibacterium acnes), which is normally present in the hair follicle. [merckmanuals.com]

Acne treatment depends on the severity of the condition. Mild acne requires the simplest treatment that poses the fewest risks of side effects. More severe acne or acne that does not respond to preliminary treatment requires additional treatment. [merckmanuals.com]