Acne is a skin condition in which the pores become clogged and inflamed, causing various types of blemishes on the face, neck, chest, or back. A number of factors contribute to acne, including problems with the shedding of dead skin cells, excess oil production, and multiplication of bacteria that normally exist in the skin. Your pores are microscopic openings in your skin which connect to a tiny hair follicle and an oil, or sebaceous (suh-BAY-shus) gland. Ordinarily, this oil, or sebum (SEE-buhm) exits the follicle through the pore, washing out bacteria and debris with it. In some people, however, the skin cells clump together and block the follicle. Oil and bacteria are trapped inside, leading to infection. This causes bumps like whiteheads, which stay beneath the skin; blackheads, in which the trapped sebum reaches the pore opening; and more serious acne lesions (LEE-zhuns) which may be red, swollen, and painful. Acne usually increases in severity with the amount of oil that your body makes. Hormonal fluctuations, sun exposure, and the mineral iodine can all boost oil production, compounding the problem. Prolonged stress is also known to worsen acne, though doctors aren't sure why.