Even though all acne spots and blemishes start to develop in the same way, they can acquire many different appearances and may react differently for different people, leading to different types of acne. All acne originates with one basic lesion: the comedo, an enlarged hair follicle blocked with sebum made from oil, dead skin cells and bacteria. The comedo stays below the surface of the skin waiting for the optimum conditions to develop into a swollen lesion. As more sebum keeps on being produced, bacteria thrive within the swollen follicle. The neighboring skin becomes gradually more inflamed as the white blood cells fight against the trespasser. The way the comedo develops and the way the immune system responds detemrine the nature of the acne and the type of lesion that is seen.

There is a list below with a brief classification and definition of each feature that can be seen in acne. Acne lesions extend in severity from comedones (mild) to nodules and cysts (nasty).

Comedo is a type of acne in which a sebaceous follicle is blocked with sebum, dead cells from inside the sebaceous follicle, and sometiems small hairs, and bacteria. If a comedo is open, it is usually called a blackhead since the outside of the plug in the follicle has a blackish outward appearance. A closed comedo is commonly known as a whitehead. Its appearance is that of a skin-colored, or a somewhat swollen, “bump” in the skin. The difference in color between the whitehead and the blackhead lies on the fact that the aperture of the plugged sebaceous follicle to the skin’s surface is closed or very narrow, unlike the expanded follicular opening of the blackhead.

Another type of acne feature presentation is a papule. A papule is a tiny (5 millimeters or less), solid lesion vaguely prominent above the surface of the skin. A group of very small papules and comedones may be practically undetectable but have "a sandpaper" feel to the touch. A papule results from a limited local cellular response to the process of acne.

Pustule: a pustule is a frail type of acne lesion with the figure of a dome. It contains some pus, which in general consists of a concoction of white blood cells, dead skin cells, bacteria, and plasma fluid. A pustule that develops over a sebaceous gland may or may not have a hair in the center. Acne pustules that cure devoid of continuing to cystic form usually leave no scars.

Macule: a macule is the short-term red spot that is left by a healed acne lesion. It is flat, usually red or reddish, with a distinct border. A macule is a type of acne feature that may endure for a long time, maybe weeks, before vanishing. Macules can contribute to the “red face” appearance of acne if a number of them are present together at one time.

Nodule: a nodule is like a papule in that it is a solid, dome-shaped lesion. However, unlike a papule, a nodule may be very painful. This type of acne is characterized by swelling. The nodule reaches into deeper levels of the skin and may produce tissue damage, finally resulting in scarring. Nodular acne is one of the most severe types of acne to have.

An even more severe type of acne is a cyst. A cyst is a lesion that resembles a sac, containing liquid substances composed of white blood cells, dead cells, and bacteria. It is reminiscent of a pustule; it can become really inflamed, reaches deep skin layers, can be very painful, and may result in scarring. The main difference is that cysts outsize pustules. Cysts and nodules usually occur together in severe types of acne.

The features above are the main characteristics of acne that are usually seen. You might see just one type of acne feature or you might see several types together in the same region of skin.