Whiteheads and blackheads are fundamentally related skin lesions that represent the earliest stages of acne formation. Both are classified scientifically as comedones, which are simply clogged hair follicles. Understanding the difference between these two types of blemishes involves examining where the blockage occurs relative to the skin’s opening.
Shared Origin: The Blocked Follicle
Both whiteheads and blackheads begin forming within the pilosebaceous unit, which consists of a hair follicle and its attached sebaceous gland. This gland produces sebum, an oily substance that normally lubricates the skin and exits through the pore opening.
Blockage begins when excess sebum production combines with hyperkeratinization—the improper shedding of dead skin cells (keratinocytes) lining the follicle. Instead of flaking off, these sticky cells accumulate and bind with the sebum, creating a solid plug.
Hormonal changes often increase sebaceous gland activity, leading to sebum overproduction. This excess oil contributes to the formation of the initial microcomedo, a microscopic blockage. The subsequent difference in appearance depends entirely on whether this plug remains trapped beneath the skin or is exposed to the air.
Whiteheads: The Mechanism of a Closed Comedone
Whiteheads are known as closed comedones because the blockage remains sealed off from the external environment. The mixture of sebum and dead skin cells clogs the hair follicle but stays trapped beneath a thin layer of skin. This covering prevents the material inside from being exposed to oxygen.
Because the contents are sealed, the lesion appears as a small, raised bump that is white or flesh-colored. This appearance is due to the accumulated material pushing against the skin without any chemical reaction to darken it. Closed comedones are often smooth and typically do not exhibit the redness or inflammation associated with more advanced forms of acne.
Since the pore opening is completely closed, the contents cannot be easily extracted. The development of a closed comedone means the material has dilated the hair follicle while the surface integrity of the skin remains intact.
Blackheads: Oxidation in an Open Comedone
Blackheads are classified as open comedones, meaning the follicular plug has expanded to stretch the pore opening. Because the opening is widened, the trapped mixture of dead cells and sebum is exposed directly to the air. This exposure initiates a chemical process known as oxidation.
The dark color that gives the blackhead its name is not caused by dirt, a common misconception, but rather by the oxidation of the material inside. Specifically, the melanin pigment found in the dead skin cells and the lipids within the sebum undergo this reaction when exposed to atmospheric oxygen. This chemical change causes the tip of the plug to turn a dark brown or black color.
The dark appearance is similar to how a cut apple turns brown when left out, demonstrating a non-dirt-related oxidation process. Open comedones often appear as small dark dots on the skin, and they can sometimes be yellow or yellowish-black. The open nature of the pore distinguishes them from whiteheads, even though the material forming the blockage is essentially the same.