Pimple. Blemish. Zit. Blackhead. Breakout. Acne. Whatever you call them, you want them gone. And whether you have one or 10 you feel like everyone is looking at your pimples instead of you. So, what causes acne to occur?

Acne—called acne vulgaris in the medical community—is a disorder of the oil glands and pores in the skin. That's why it shows up where you have the most oil glands—the face, chest and upper back.

The main causes of acne are:

1. Hormones—especially androgens, hormones that stimulate sebaceous (oil-producing) glands.
2. Clogged pores from the abnormal shedding of skin cells.
3. Excess sebum (oil) production from the sebaceous glands.
4. Bacterial build-up in the sebaceous glands.

Sebaceous glands are attached to hair follicles, tiny shafts in the skin where hair grows. Normally, oil spreads from a follicle to the skin's surface to lubricate skin. Follicles shed skin cells from their lining. When the body produces excess oil and dead skin cells stick together in the follicle—as often happens during adolescence—you get acne. The cells stick together with excess oil to form a hard plug that blocks the pore. The plugged follicle is called a comedo. Whiteheads and blackheads are comedones.

The oil becomes a breeding ground for bacteria, especially Propionibacterium acnes. But in the process, the follicle wall can burst, sending its contents into surrounding tissues. The body's response is to send in white blood cells to clean things up. This causes swelling, inflammation, pain and pus. In other words, you've got a pimple. Papules, pustules and cysts are types of pimples.