Final answer:
Acne vulgaris is caused by a combination of factors including the release of sebum, blockage of hair follicles, and infection by acne-causing bacteria like Propionibacterium acnes.
Step-by-step explanation:
Acne is a skin disturbance that occurs on areas of skin with sebaceous glands. It is most common during puberty due to hormonal changes, but can also happen in infants and continue into adulthood. Hormones stimulate the release of sebum, which, along with keratin, can block hair follicles. This blockage, along with acne-causing bacteria like Propionibacterium acnes, can lead to redness, inflammation, and potential scarring.