There are various types of blemishes, or pimples, defined primarily by their size and whether they are "inflammatory" or "noninflammatory."

Microcomedo

The first and smallest type of lesion is a clogged pore called a microcomedo. This tiny comedo occurs at the earliest stages when the follicle walls are just beginning to be stretched by trapped sebum. Microcomedones are so small that they cannot be seen without a microscope. If the microcomedo continues to develop and then ruptures, an inflammatory lesion will occur.

Noninflammatory lesions: blackheads and whiteheads

Blackhead

If a microcomedo doesn't rupture, it can progress into either an open comedo (blackhead) or closed comedo (whitehead), both of which are noninflammatory.

In an open comedo, or blackhead, the contents of the follicle are firmly impacted inside. The tightly compacted cells and sebum give the follicle its 'black' appearance. The dark color does not indicate the presence of dirt. Blackheads can't be washed away. They can, however, be removed with a comedo extractor by a physician. They should not be squeezed, as squeezing can irritate the skin and cause or spread inflammation.

Closed comedones, or whiteheads, are skin-colored or white, and just look like small bumps on or under the skin.

Inflammatory lesions: papules, pustules, and nodules

Papule	Pustule

Inflammatory acne lesions are the ones that have a red color, often making a ring around the pimple itself. They result when sebaceous material from the comedo gets into the surrounding tissue and causes an inflammatory reaction. Picking and squeezing acne lesions is a frequent cause of lesion rupture and inflammation, which increases the risk for scarring. For this reason, it is important to leave acne lesions alone.

There are basically three types of inflammatory acne lesions: papules, pustules and nodules, shown in the diagrams. Papules and pustules are relatively small, while nodules are larger, more severe acne lesions.

Papules (typical pimples) are small, firm, reddish lesions and are sometimes considered an intermediate step between noninflammatory lesions and clearly inflammatory lesions. Papules are mildly inflamed, showing redness but no apparent pus.

Pustules are small, like papules, but are clearly inflammatory. Pustules are small round lesions that contain visible pus. The pus is underneath the surface of the skin. Pustules do not usually contain a lot of bacteria. The inflammation is generally caused by chemical irritation from sebum components such as free fatty acids.

Nodules (sometimes referred to as cysts) are the most extreme lesions seen in acne. They are large inflammatory lesions that contain large amounts of pus. Nodules develop when the contents of a comedo have been spilled into the skin and a tremendous local immune response occurs, producing pus. These large lesions can extend deeply into the skin and can be very painful. Scarring is more frequent following healing of nodules than of other types of acne lesions.

Dr. Kiran Godse Skin Specialist Laksh-Deep Hospital