There are several different types of acne. Acne can be both inflammatory and non-inflammatory. You may have predominantly one form of acne or a combination at one time.

The non-inflammatory acne, also called comedones, is formed when the sebaceous glands overproduce oil that is not released through the pores. A plug is formed that may be white or black depending on if the acne is open or closed. Closed comedones (whiteheads) look like white pinheads just under the skin. In open comedones (blackheads) have the excessive sebum permeated out allowing oxidation of the debris. This results in black dots in the pores and is not due to dirt as many people think.
If the acne progress and the blocked follicle becomes invaded by the bacteria P. acne, inflammation occurs. P. acnes is a naturally occurring skin bacteria and is not harmful in small quantities. Trapped sebum is ideal for the bacteria to live and multiply causing increased number in a short time. This triggers an immune response resulting in inflammation.

Inflamed pimples with a rough texture near the skin’s surface are called papules. If the inflammation occurs deeper in the tissue pustules are formed. These are filled with pus and appear as red bumps with a white or yellowish interior. The most severe form of acne consists of cysts and nodules. They are large and painful pus-filled regions deep in the skin. They usually last for several weeks or months and often leave marks and permanent scars.

Inflamed acne will heal eventually but needs to be treated early to prevent scarring. In some cases, the area of the breakout remains discolored (post-inflammatory hyperpigmentation) for several months after the inflammation. This is often more noticeable in people with darker skin. Some pimples and acne do not fully fade out and leave permanent scars on the skin.