People with acne frequently have a variety of lesions, some of which are shown in the diagrams below. Acne can be divided into 2 major categories: noninflammatory and inflammatory. This categorization is not always clear-cut because lesions, which start out noninflammatory, can become inflammatory over time.
Noninflammatory acne. The basic acne lesion is known as a comedone and is simply an enlarged and plugged hair follicle.. This lesion is formed due to excess oils and abnormal epithelial (outer skin layers) shedding.
- Closed comedones are lesions in which the hair follicle pore remains closed on the skin surface. There is no direct exposure to oxidation and what you see is a whitish-pink appearance. This has come to be known as a whitehead.
- Open comedones, by contrast, are lesions in which the hair follicle pore remains open to the air. The oil and shedding epithelial plug is exposed to the air and appears dark to the eye. This has come to be known as a blackhead. Contrary to popular belief, blackheads are not trapped dirt underneath the skin.
Inflammatory acne. What people commonly refer to as a pimple, zit or “skin blemish” is usually an inflammatory acne lesion. There are several different types of inflammatory acne lesions:
- Papules are inflamed closed comedones that are small, pink, swollen, inflamed and tender.
- Pustules are closed comedone papules that are topped by pus-filled lesions with a reddish appearance at the base. The pustular heads (pimples) come in different sizes and shapes.
- Nodules are the large, painful, swollen, semi-solid lesions that have ruptured under the deep skin. Nodules have known to cause deep scarring.
- Cysts are pus-filled nodules in the deep skin. These lesions can also cause scarring.