Acne is the most common skin disease in the world — 80 percent of all people experience an acne breakout at some point in their lives, often during the teenage years. Acne is a skin condition in which the pores become clogged with sebum (oil) and dead skin cells. These clogs are referred to as comedones or blackheads and whiteheads. Propionibacterium acnes bacteria found on the skin can becomes trapped in these clogged pores. As the bacteria thrive on the sebum and pustule begins to form. Over time this triggers an inflammatory response from and a deep tender cystic lesion may form, which may eventually lead to follicle rupture if untreated.

Acne most frequently affects the face, neck, back, chest and shoulders, areas that tend to have the greatest concentration of oil producing glands.

There are many different types of acne lesions:

Blackheads are open but clearly clogged pores that have a dark center. These are blockages that have made their way to your skin’s surface. When the oil makes contact with the air, the blockage turns dark.
Whiteheads are hair follicles that are blocked and bulge. They form a cap, as it were, that’s white. Whiteheads occur below the skin.
Papules are just small bumps on the skin, usually pinkish in color, but tender to the touch.
Pustules are papules that are topped with pus. Pustules usually have visible red inflammation in the surrounding skin.
Cysts and Nodules are clogs deep beneath the skin. They don’t have a “head,” as a blackhead or whitehead do. They are painful, larger than pimples, solid to the touch and can leave scars.

There are different levels of acne severity:

Mild acne is the most common. It includes blackheads and whiteheads. If you only have a few clogged pores or they’re in an isolated spot, your acne is “mild.”
Moderate acne means you have more pimples than blackheads or whiteheads. With this type of acne, you may notice that some of your pimples have red skin or inflammation around them.
Severe acne is when you have nothing but pimples, both those that are small bumps and those that are yellowish and filled with pus. Additionally, severe acne can include nodules or cysts.