In people who have acne, dead skin cells mix with sebum (oil) produced by the skin and plug up hair follicles in the skin. Bacteria that grow in the plugged hair follicles cause more skin irritation. Acne commonly starts in the early teen years, when the oil glands in the body start making more sebum.

When the hair follicle becomes plugged with oil and skin cells, a “whitehead” occurs. If the follicle is plugged near the surface of the skin and air touches the plug, it turns black and is called a "blackhead." A blackhead isn't caused by dirt.

If the wall of a plugged hair follicle breaks, the area swells and turns into a red bump. If the hair follicle wall breaks near the skin surface, the bump usually becomes a pimple. If the wall breaks deep in the skin, acne nodules or cysts can form. This is called "cystic acne."

Both boys and girls get acne. But it may be worse in boys because they have more skin oils. For many people, acne symptoms fade by the age of 25, but they can continue well into the adult years.

Family history also plays a role. If your mother and father had bad acne, you may have it, too.

Your immune system plays a role too. Some people are extra sensitive to the bacteria that get trapped in their hair follicles.

Many treatments are available for acne, including over-the-counter and prescription medicines.

Benzoyl peroxide and salicylic acid are the most common and most effective over-the-counter medicines for acne. These medicines kill bacteria, dry up the oil and make your skin peel off. They are available in many forms, such as gels, lotions, creams, soaps or pads. Keep in mind that it can take up to 8 weeks before you notice an improvement in the appearance of your skin. If an over-the-counter acne product doesn't seem to help after 2 months, talk to your doctor.

In some people, over-the-counter acne medications may cause side effects such as skin irritation, burning or redness. Tell your doctor if you have side effects that are severe or that don't go away over time.

If over-the-counter medicines are not effective, your doctor may prescribe a retinoid cream or gel. Retinoids, such as tretinoin and adapalene, are usually applied to the skin once a day. Be sure not to get them near your eyes, mouth and the area under your nose.

If you use a retinoid, you must avoid the sun or use a strong sunscreen because this medicine increases your risk of getting a sunburn. Women who are pregnant or may become pregnant should not use a retinoid called tazarotene because it can cause birth defects.

If your acne is severe, your doctor may prescribe an antibiotic to treat it. Antibiotics such as minocycline, doxycycline and tetracycline reduce bacteria and inflammation, and can be used in combination with other treatments for acne, such as benzoyl peroxide. Antibiotics can be taken by mouth or used on the skin as a lotion, cream or gel.

Isotretinoin may be used to treat severe cystic acne that doesn't get better with other treatments. It's a pill that is taken once a day by mouth for 15 to 20 weeks.

Pregnant women should never take isotretinoin. It can cause serious birth defects and miscarriages. A woman who is taking isotretinoin must use 2 types of birth control or not have sex starting 1 month before she begins taking the medication and lasting 1 month after she stops taking it.

There is a possibility that other serious side effects may occur, so people taking isotretinoin should be closely monitored by their doctor.

Acne, especially cystic acne, can cause scars in some people. You can help reduce scarring by not squeezing or picking at blemishes. Also, avoid scrubbing your skin. If you do get scars, treatments to help reduce scarring are available.