context: If there's one thing you can count on as a teen, it's acne. More than 85% of teenagers have this common skin problem, which is marked by clogged pores (whiteheads, blackheads), painful pimples, and, sometimes, hard, deep lumps on the face, neck, shoulders, chest, back, and upper arms. If your mom and dad had acne, chances are good that you will, too. But there are many ways to prevent (and treat) acne today to keep the condition minimal, prevent scarring, and leave your skin glowing. To understand acne, you need to know how your skin works. The pores in your skin contain oil glands. When you hit puberty, there's an increase in sex hormones called androgens. The excess hormones cause your oil glands to become overactive, enlarge, and produce too much oil, or sebum. When there's too much sebum, the pores or hair follicles become blocked with skin cells. The increase in oil also results in an overgrowth of bacteria called Propionibacterium acnes. If blocked pores become infected or inflamed, a pimple -- a raised red spot with a white center -- forms. If the pore clogs, closes, and then bulges, you have a whitehead. A blackhead occurs when the pore clogs, stays open, and the top has a blackish appearance due to oxidation or exposure to air. ( This has nothing to do with skin being "dirty"). When bacteria grow in the blocked pore, a pustule may appear, meaning the pimple becomes red and inflamed. Cysts form when the blockage and inflammation deep inside pores produce large, painful lumps beneath the skin's surface. Hormonal changes related to birth control pills, menstrual periods, and pregnancy can trigger acne. Other external acne triggers include heavy face creams and cosmetics, hair dyes, and greasy hair ointment -- all of which can increase blockage of pores. Clothing that rubs your skin may also worsen acne, especially on the back and chest. So can heavy sweating during exercise, and hot, humid climates. Stress is known to trigger increased oil production, which is why many teens have a new crop of pimples on the first day of school or just before that big date. While the symptoms of acne vary in severity, you'll notice these signs on areas of your body with the most oil glands (the face, neck, chest, back, shoulders, and upper arms): Clogged pores (pimples, blackheads, and whiteheads) Papules (raised lesions) Pustules (raised lesions with pus) Cysts (nodules filled with pus or fluid) The least severe type of acne lesion is the whitehead or blackhead. This type is also the most easily treated. With more extensive acne, you may need prescription medications to ease inflammation, bacterial infection, redness, and pus. The treatment usually depends on how serious the problem is. For instance, if you have an occasional inflamed pimple, you may use skin compounds containing: Azelaic acid Benzoyl peroxide Glycolic acid Lactic acid Retinoids (medications that come from vitamin A) Salicylic acid Various fruit acids Benzoyl peroxide reduces oil production and has antibacterial properties. But use it carefully, as it might leave your skin dry and flaky. ( It can also bleach out clothing, towels and bedsheets.) Try to use it just before bedtime. Resorcinol and sulfur, as well as prescription retinoids and prescription antibiotics applied to skin, can reduce blackheads, whiteheads, and inflamed pustules. When many pustules or cysts appear on the face and upper body, you'll need an oral antibiotic. Your doctor also can inject cysts with anti-inflammatory steroid solutions to help decrease their size. For persistent acne, antibiotics (taken by mouth or applied to the skin) are generally used. Some antibiotics have both antibacterial and anti-inflammatory properties. These are often prescribed for short-term use (usually a few months). Because acne is linked to hormones, some oral contraceptives (birth control pills) may help. But not all birth control pills stop acne, and some make it worse. Spironolactone, a hormone blocker, can be used for teenage girls who have acne. Isotretinoin, a prescription medication you take orally, may help control severe acne, which is characterized by many large cysts on the face, neck, and upper trunk and scarring. Pregnant women or women who might become pregnant can't use this medication, as it's linked to birth defects. Isotretinoin can give people very dry skin, eye dryness, and irritation and requires blood tests to monitor for liver inflammation, high blood fat content, and bone marrow suppression. It can also be very expensive. So its use is restricted to the most severe cases for which other treatments haven't worked. There are some steps you can take to prevent acne. To prevent oily skin that can contribute to acne, keep your skin clean. Wash your face and neck twice daily with mild soap and warm water. But never scrub your face! That can irritate your skin and worsen acne. Whether you have a few pimples or more serious acne, talk to your primary health care provider about treatments. Treating acne early is the key to avoiding permanent scarring.