Blackheads form when a hair follicle becomes clogged with a mix of dead skin cells and oil, and the plug sits open at the skin’s surface. That opening exposes the contents to air, triggering a chemical reaction that turns the plug dark. The process starts weeks before anything becomes visible, and it involves a chain of events inside the pore that most people never think about.
What Happens Inside the Pore
Every pore on your face contains a tiny hair follicle and an oil-producing gland. Under normal conditions, dead skin cells lining the inside of the follicle shed into the pore and get pushed out by a steady flow of oil (called sebum). The system is self-cleaning.
A blackhead begins when that shedding process breaks down. The skin cells lining the upper part of the follicle start sticking together instead of sloughing off. They develop stronger connections between them, forming a thicker, more cohesive layer that doesn’t release properly. This clumping creates a tiny plug deep in the pore, known as a microcomedone, roughly eight weeks before anything shows up on the surface of your skin. During those weeks, the plug grows as more cells and oil accumulate behind it.
At the same time, the oil glands keep producing sebum. With the exit partially blocked, that oil backs up. The follicle stretches and eventually widens enough that the plug reaches the surface and sits in an open pore. That open pore is the key distinction between a blackhead and a whitehead. A whitehead is the same type of plug, but it’s sealed beneath a thin layer of skin.
Why the Plug Turns Dark
The dark color of a blackhead isn’t dirt. It’s the result of oxidation. When the plug is exposed to air at the surface, two things happen. First, melanin (the same pigment that gives your skin its color) is present in the dead skin cells packed into the plug. Melanin is a redox-active molecule, meaning it reacts with oxygen and shifts into a darker oxidized state. Second, a component of sebum called squalene, which makes up about 10 to 15 percent of the oil on your face, is highly susceptible to oxidation. When squalene reacts with oxygen, UV light, or airborne pollutants like ozone, it produces byproducts that darken the plug further and can also trigger inflammation around the pore.
Together, oxidized melanin and oxidized sebum create the characteristic black or dark brown appearance. The deeper the plug and the longer it’s been exposed, the darker it tends to look.
Hormones Drive the Oil Supply
Your oil glands don’t operate on autopilot. They’re directly controlled by hormones, particularly androgens. Testosterone circulating in the blood reaches the sebaceous gland, where an enzyme converts it into a more potent form called DHT. This conversion happens right inside the gland cells, which carry all the necessary enzymatic machinery. DHT binds to receptors in those cells with greater strength and stability than testosterone itself, making it the primary driver of oil production.
People with acne-prone skin produce higher rates of both testosterone and DHT in their skin compared to those without acne. This is why blackheads commonly appear during puberty, around menstrual cycles, and during other hormonal shifts. It’s not just that the glands produce more oil. The composition of that oil changes too, becoming more likely to clog the follicle.
Another hormonal player is insulin-like growth factor 1, or IGF-1. This growth signal increases oil production in sebaceous gland cells and also ramps up inflammatory activity. IGF-1 levels rise when your body produces more insulin, which connects oil production to what you eat.
How Diet and Environment Factor In
High-glycemic foods (white bread, sugary drinks, processed snacks) cause rapid spikes in blood sugar and insulin. That insulin surge raises IGF-1 levels, which in turn stimulates the oil glands to produce more sebum. Lab studies on human sebaceous gland cells confirm that IGF-1 significantly increases lipid production and activates the genetic pathways responsible for fat synthesis in those cells. This doesn’t mean a single cookie causes a blackhead, but a consistently high-glycemic diet creates an environment where your oil glands run hotter than they otherwise would.
Environmental pollutants also play a measurable role. Ozone, tobacco smoke, and UV radiation all accelerate the oxidation of squalene on your skin’s surface. The byproducts of that reaction are comedogenic, meaning they actively promote pore clogging. UV exposure also depletes vitamin E in the skin, which normally acts as a protective antioxidant. When UV and air pollution combine, the effect on sebum oxidation is additive, not just overlapping. Living in a high-pollution area or spending significant time outdoors without protection can make existing blackheads worse and encourage new ones to form.
Why Some People Get More Blackheads Than Others
The factors that create blackheads are universal, but their intensity varies widely from person to person. Genetics determine how large your oil glands are, how many androgen receptors they carry, and how efficiently your skin cells shed. Someone with naturally larger, more active sebaceous glands and stickier follicular lining will develop blackheads more readily, even with identical skincare habits to someone who doesn’t.
One specific factor researchers have identified is a decrease in linoleic acid within sebum. When oil glands overproduce, the concentration of this particular fatty acid drops. Lower linoleic acid levels cause the skin cells lining the follicle to behave abnormally, differentiating in a way that promotes clumping. So excess oil production doesn’t just fill the pore. It changes the chemical environment in a way that makes the plug more likely to form in the first place.
How Treatments Target the Plug
The two most effective approaches to blackheads work at different stages of the process. Retinoids, which are vitamin A derivatives, normalize how skin cells inside the follicle grow and shed. They address the root cause by preventing cells from clumping together, keeping the pore lining thin and letting debris flow out naturally. This is why dermatologists consider retinoids the gold standard for comedonal acne (acne dominated by blackheads and whiteheads rather than inflamed pimples).
Salicylic acid works differently. It’s oil-soluble, which means it can penetrate into the sebum-filled pore and dissolve the material holding the plug together. It essentially exfoliates inside the follicle rather than on the skin’s surface. Alpha-hydroxy acids like glycolic acid, by contrast, work better on the surface in water-rich areas of the skin. Combining a retinoid with salicylic acid targets both the cellular stickiness and the oily buildup, which is why many treatment plans use both.
Neither approach works overnight. Because microcomedones form roughly eight weeks before they’re visible, you’re always treating plugs that are already well underway. Consistent use over several weeks is necessary to interrupt the cycle and prevent the next generation of blackheads from reaching the surface.