Blackheads form when a pore gets clogged with a mix of dead skin cells and oil, and the surface of that plug is exposed to air. The exposure triggers a chemical reaction that turns the plug dark, giving blackheads their distinctive appearance. Understanding the full process, from initial clog to that characteristic black dot, helps explain why they show up where they do and what actually works to prevent them.
What Happens Inside the Pore
Every pore on your skin contains a tiny hair follicle and an oil gland. The oil gland produces sebum, a waxy lubricant that travels up through the pore to keep your skin moisturized. Dead skin cells lining the inside of the pore are supposed to shed gradually and get carried out with the oil. When that system works, you never notice it.
A blackhead starts when something disrupts the flow. Either the oil gland produces too much sebum, the dead skin cells don’t shed properly, or both. Instead of exiting the pore, the dead cells stick together and mix with sebum to form a plug. The protein keratin, which gives skin cells their structure, can form abnormally and make those cells stickier than usual, accelerating the clog. Bacteria naturally present on your skin also play a role. The most relevant species produces a biological glue essential for its survival, but when it overgrows, that glue mixes into the sebum and dead cell buildup, making the plug denser and harder for the pore to clear on its own.
At this stage, the clog is just a plug sitting inside a follicle. If skin covers the top and seals it off from air, it stays light-colored. That’s a whitehead. But if the pore remains open and the plug reaches the surface, something different happens.
Why the Plug Turns Black
The dark color of a blackhead has nothing to do with dirt. When the top of the plug sits at the skin’s surface with the pore open around it, oxygen in the air reacts with two components trapped in the material: lipids (fats from the sebum) and melanin (the pigment your skin naturally produces). This oxidation reaction darkens the exposed surface of the plug, creating the characteristic black or dark brown dot. The material deeper inside the pore remains lighter because it’s not exposed to air.
This is the same basic chemical process that turns a cut apple brown. The internal composition of a blackhead and a whitehead is nearly identical. The only structural difference is whether the pore opening is wide enough to expose the contents to oxygen.
Hormones and Oil Production
Hormones are the single biggest driver of excess sebum, which is why blackheads tend to cluster during puberty, menstrual cycles, and other hormonal shifts. Androgens, a group of hormones that includes testosterone, directly stimulate oil glands to produce more sebum. The key player is a potent form of testosterone called DHT, which is actually created inside the oil glands themselves.
Research published in Acta Dermato-Venereologica found that acne-prone skin produces 2 to 20 times more DHT than normal skin in the same areas of the body. That’s a massive range, and it helps explain why some people are far more prone to blackheads than others even with identical skincare routines. DHT doesn’t just increase the volume of oil your glands produce. It can also change the thickness and quality of keratin inside the pore and alter the composition of sebum itself, making clogs more likely on multiple fronts.
Environmental Factors That Speed Things Up
Heat and humidity create conditions that make blackheads more likely. Increased sweating doesn’t directly clog pores, but the combination of sweat, humidity, and excess oil on the skin’s surface creates a film that can trap debris over pore openings. Skin irritation and low-grade inflammation from heat exposure can also disrupt normal cell shedding inside follicles. This is why many people notice more blackheads during summer months or after workouts, particularly on the nose, forehead, and chin where oil glands are densest.
Blackheads vs. Sebaceous Filaments
Many of the tiny dark dots people try to squeeze from their nose aren’t actually blackheads. They’re sebaceous filaments, which are a completely normal part of your skin’s architecture. Sebaceous filaments are thin, threadlike structures that line the inside of oil glands and help move sebum to the surface. They’re doing exactly what they’re supposed to do.
The differences are visible if you know what to look for. Sebaceous filaments appear as flat, evenly spaced dots that are usually gray, light brown, or yellowish. Blackheads are darker, slightly raised, and look like a speck of dirt sitting in a bump. The functional difference matters even more: sebaceous filaments don’t contain a plug, so oil flows freely through the pore. Blackheads have a solid plug that blocks the pore entirely. If you squeeze a sebaceous filament, a thin, waxy thread emerges. Squeeze a blackhead, and you get a darker, firmer plug.
Removing sebaceous filaments is pointless because they refill within about 30 days. They’re part of your skin’s oil delivery system, not a defect.
How Prevention Targets Each Step
Because blackhead formation is a multi-step process, the most effective prevention strategies interrupt one or more of those steps. The goal is either reducing the amount of oil in the pore, keeping dead skin cells from accumulating, or both.
Salicylic acid is the most widely recommended ingredient for blackheads specifically because it’s oil-soluble, meaning it can penetrate into the pore rather than just working on the skin’s surface. Once inside, it dissolves the cement-like substance that holds dead skin cells together, causing the compacted cells to swell, soften, and shed. This breaks apart existing plugs and prevents new ones from forming. It works through a process called desquamation, essentially accelerating the natural shedding cycle that went wrong in the first place.
Retinoids work differently, normalizing the way skin cells mature and shed so they’re less likely to clump together inside the follicle. Products that reduce oil production target the sebum side of the equation. No single approach addresses every contributing factor, which is why consistent routines that combine gentle exfoliation with oil control tend to produce better results than any one product alone.
Keeping skin clean after sweating, avoiding heavy or occlusive products on blackhead-prone areas, and resisting the urge to squeeze (which can widen pores and trigger inflammation) all reduce the chances of new clogs forming. Since hormonal factors drive much of the underlying oil production, some people find that blackheads persist regardless of topical care, particularly during hormonally active life stages.