An acne breakout starts in the skin's tiny holes, commonly called pores. It takes about two to three weeks before a blemish shows up on the skin's surface.

Deep within each pore is a sebaceous gland that works to produce sebum, an oil that keeps skin soft and moist. As the skin renews itself, old skin cells die and are shed off. But some people shed skin unevenly and as a result, dead cells mix with sebum and clump together to form a sticky plug. This plug traps oil and bacteria inside the pore — the beginning of a blemish.

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