Acne lesions come in different forms. A characteristic they share is a build-up of sebum (oil).
Open Comedone (Blackhead) – a build-up of sebum, dead skin cells, bacteria, and other debris inside the follicle. Appears dark because the oil has been oxidized (exposed to oxygen). An open comedone may be referred to as congestion.
Closed Comedone (Whitehead) – a build-up of sebum, dead skin cells, bacteria, and other debris inside the follicle. Appears flesh colored. Because the follicle opening is blocked, the sebum has NOT been oxidized. A closed comedone may also be referred to as congestion.
Papule – a small bump on the skin, does NOT contain pus.
Pustule – a bump that is filled with pus (white blood cells mixed with follicular debris). Commonly called a pimple. Larger than a papule
Nodule – a very deep lesion, similar to a papule. A nodule often involves more than one follicle.
Cyst – a closed sac of tissue. May contain air, fluid, dead skin cells, and pus. In the case of acne, a cyst is a nodule with a large amount of inflammation (white blood cells). Acne scarring is due to cysts that rupture.
Milia – tiny, white, hard, pearly masses under the skin, typically around the eyes and nose. Composed of keratin (trapped dead skin cells). Often mistaken for a whitehead. These tiny cysts have no opening, so they cannot be extracted and must be excised with a lancet.
Open and closed comedones are categorized as non-inflammatory acne. Papules and pustules are inflammatory lesions.
Grades of Acne
Grade 1 – minor breakouts, mostly open comedones, some closed comedones, a few papules
Grade 2 – many closed comedones, more open comedones, occasional papules and pustules
Grade 3 – red and inflamed skin, many comedones, papules, and pustules
Grade 4 – cystic acne, scars are common