Blackheads (Open Comedones)
A comedo is a clogged hair follicle (pore) in the skin. A comedo can be open (blackhead) or closed by skin (whitehead). Being open to the air causes oxidization, which turns it black.
Part of: Acne Lesions, Comedones
See also: Acne Skin Care
About Blackheads
The basic acne lesion, called the comedo (KOM-e-do), is simply an enlarged and plugged hair follicle. If the comedo stays beneath the skin, it is called a closed comedo and produces a white bump called a whitehead.
A comedo that reaches the surface of the skin and opens up is called an open comedo or blackhead because it looks black on the skin’s surface. This black discoloration is due to changes in sebum as it is exposed to air. It is not due to dirt. Both whiteheads and blackheads may stay in the skin for a long time. NIH – National Institute of Arthritis and Musculoskeletal and Skin Diseases