A blackhead is a tiny plug made of skin oil, dead skin cells, and a tough protein called keratin, all packed into a pore that has stretched open at the surface. The dark color isn’t dirt. It’s the result of a chemical reaction between the plug’s natural pigment and the air.
The Three Main Ingredients
Every blackhead starts with the same basic materials your skin produces on its own. The first is sebum, the oily substance your body makes to keep skin moisturized. The second is dead skin cells. Your skin constantly sheds old cells from the lining of each pore, and normally these cells travel up and out without issue. The third is keratin, a fibrous structural protein that gives skin its toughness.
In a healthy pore, sebum flows up through the opening and spreads across the skin surface, carrying dead cells along with it. In a blackhead, that process breaks down. The dead cells don’t shed properly. Instead, they stick together and mix with sebum and keratin to form a dense, waxy plug that fills the pore from the inside. The result is a column of material that can sit in the pore for weeks or months, slowly growing as more oil and cells accumulate behind it.
Why the Plug Turns Black
The most persistent myth about blackheads is that the dark tip is embedded dirt. It’s not. The color comes from melanin, the same pigment that gives your skin, hair, and eyes their color. Dead skin cells contain melanin, and when that melanin sits at the surface of an open pore and makes contact with air, it oxidizes. That chemical reaction turns the exposed tip of the plug dark brown or black.
This is also why whiteheads stay light-colored. A whitehead contains the same mixture of oil, dead cells, and keratin, but a thin layer of skin covers the pore opening, sealing the plug away from oxygen. No air contact means no oxidation, and the plug stays white or flesh-toned. The only structural difference between a blackhead and a whitehead is whether the pore opening is sealed or exposed.
Bacteria Living Inside the Plug
Blackheads aren’t sterile. The warm, oily, low-oxygen environment inside a clogged pore is an ideal home for certain bacteria. Research analyzing the contents of comedones found that the dominant bacteria inside the plug belong to the genus Cutibacterium, particularly the species C. acnes. On the surface of healthy skin, Staphylococcus bacteria tend to dominate. But inside a clogged pore, C. acnes takes over because it thrives on sebum and can flourish without much oxygen.
In a simple blackhead, these bacteria don’t usually cause problems. They’re the same organisms that live on everyone’s face. But when C. acnes populations grow large enough inside a plugged pore, their metabolic byproducts can trigger an immune response. That’s what turns a quiet blackhead into an inflamed, red pimple. The bacteria don’t invade the skin so much as they irritate it from within, and the body responds with swelling and redness.
How the Plug Forms
Blackheads don’t appear overnight. They begin as microscopic clogs called microcomedones, too small to see or feel. Inside the pore, cells lining the follicle wall start to shed faster than normal or clump together instead of exiting smoothly. Hormones, particularly androgens, drive this process by increasing sebum production and changing how pore-lining cells behave.
As keratin and dead cells accumulate, the tiny clog thickens into a closed comedone, a small bump under the skin. Over time, the growing plug pushes outward and stretches the pore opening. Once the opening dilates enough that the plug’s surface is directly exposed to air, you have a blackhead. Visible pores on the face typically range from 0.1 to 0.6 mm across, but a pore distended by a blackhead can sit at the larger end of that range or beyond, which is why blackheads often look like prominent dark dots.
This process can take weeks. It’s gradual enough that most people don’t notice a blackhead forming until it’s already established.
What Happens When You Squeeze
When you press on a blackhead, you’re trying to force a waxy, compacted plug back through an opening that may be narrower than the plug itself. Sometimes it works cleanly. Often it doesn’t. Uneven pressure can rupture the follicle wall below the skin surface, pushing the plug’s contents (bacteria, sebum, dead cells) into the surrounding tissue rather than out through the pore. Your immune system treats this as an invasion, flooding the area with inflammation.
The result can be a pimple far worse than the original blackhead, sometimes a deep, painful cyst. Repeated squeezing in the same area can also cause post-inflammatory dark spots or, in more severe cases, permanent scarring from fibrosis, where the body replaces damaged tissue with dense scar tissue that doesn’t function like normal skin.
How Treatments Dissolve the Plug
The most widely used ingredient for blackheads is salicylic acid, and it works because of a specific chemical property: it dissolves in oil. Unlike water-based exfoliants that only work on the skin surface, salicylic acid is lipophilic, meaning it can mix with the oily sebum inside a pore and penetrate the plug itself.
Once inside, it doesn’t dissolve keratin directly, as was once believed. Instead, it breaks apart the connections between cells. Skin cells stick together through protein structures called desmosomes, and salicylic acid extracts key proteins from those junctions. Without those anchors, the compacted dead cells loosen from each other and detach, allowing the plug to break apart and clear out through the pore opening naturally. This is why consistent use over several weeks tends to work better than a single application. The acid gradually disassembles the plug from within rather than forcing it out mechanically.
Retinoids work through a different route, normalizing the way pore-lining cells shed so they stop clumping in the first place. This addresses the root cause rather than clearing existing plugs, which is why dermatologists often recommend using both approaches together.