Acne can occur due to several different reasons, but the main reason that acne occurs is due to blocked pores or hair follicles from oil, dead skin cells, or bacteria. Your pores are openings to hair follicles and oil glands, also known as sebaceous glands. The sebaceous glands produce oil, or sebum, to lubricate your skin, keeping it soft and moist. However, if the follicles and glands produce too much oil, acne can occur. An overproduction of sebum leading to acne is typically caused by hormonal imbalances or changes, such as those that occur during menstrual cycles, pregnancy, or puberty. Other things that can cause acne include medications that contain corticosteroids, lithium, or testosterone, diets rich in carbohydrates, and stress. In some cases, the bacterium known as Propionibacterium acnes (P. acnes), which lives in the oily regions of your pores, can lead to acne or infected pimples.