Glands at the base of hair follicles make oil. The oil travels up the hair shaft. Oil trapped inside follicles causes acne.

Acne also often shows up on the chest. It can also appear on the buttocks.

Hormones, your genes, greasy makeup, and certain medicines are more likely to cause skin blemishes. Pimples are not caused by dirty skin, or by eating pizza or chocolate. But recent studies say that sugar in your diet may affect acne. Stress does not cause acne. But stress can make acne worse. A bacteria called P. acnes may also play a role.

Dead skin cells are shed quickly inside the follicles during the teen years. The dead cells mix with oil in the glands and block follicles. This causes blackheads or pimples.

During adolescence androgen causes the oil glands at the base of follicles to get larger. The glands also make more sebum. Glands affected by the hormone are more likely to develop acne.

You should make sure all of your makeup is oil-free. This includes everything from eye shadow to hair care products. Choose products that are labeled noncomedogenic or that say they will not clog pores.

When your skin is exposed to the sun, it can become dry and irritated. This can trigger your skin to make more oil. Sun exposure also raises the risk for acne scaring. Many acne treatments also make the skin vulnerable to UV damage. You should avoid spending a long time in the sun. When you do have to be in the sun, be sure to use sunscreen that is oil-free.