Blackheads form when a pore fills with a mix of oil and dead skin cells, creating a plug that stays open at the surface. Unlike whiteheads, which are sealed shut, a blackhead’s plug is exposed to air. That exposure triggers a chemical reaction called oxidation, which turns the material dark brown or black. The color has nothing to do with dirt.
What Happens Inside the Pore
Every pore on your skin contains a tiny oil gland and, in most cases, a hair follicle. The oil gland produces sebum, a waxy substance that keeps your skin moisturized and protected. Under normal conditions, sebum flows up through the pore and spreads across the skin’s surface without any issues.
A blackhead starts when that process goes wrong in two ways at once. First, the oil gland produces more sebum than the pore can handle. Second, the skin cells lining the inside of the pore shed faster than usual and clump together instead of clearing out. These sticky cells mix with the excess oil and form a plug near the opening of the pore. Because the pore stays open rather than closing over, the top of the plug is exposed to oxygen. The fats in sebum oxidize on contact with air, turning the plug dark. That’s the “black” in blackhead.
Why Hormones Are the Biggest Driver
Oil glands are extremely sensitive to androgens, a group of hormones that includes testosterone. When androgen levels rise, oil glands ramp up sebum production, sometimes dramatically. This is the main reason blackheads first appear during puberty: androgen levels surge, oil production spikes, and pores that previously stayed clear start getting clogged. Blackhead prevalence peaks during the teenage years and gradually improves afterward as hormone levels stabilize.
Hormonal shifts later in life can trigger the same process. Menstrual cycles, pregnancy, polycystic ovary syndrome, and stopping or starting hormonal birth control all affect androgen activity. Even stress raises cortisol, which can indirectly stimulate oil production. If you notice blackheads flaring at predictable times each month, hormones are almost certainly involved.
Genetics and Pore Size
Your genes play a significant role in whether you’re prone to blackheads. Twin studies have shown that identical twins have highly correlated rates of sebum production, including the specific composition of fats in their oil. If your parents dealt with acne or visibly clogged pores, you’re more likely to as well.
What’s inherited isn’t just oil volume. Genetic factors also influence how quickly skin cells turn over inside the follicle. Some people shed keratinocytes (the cells lining the pore) at a faster rate, which means more cellular debris is available to mix with sebum and form plugs. Pore size itself is partly genetic too. Larger pores hold more material, making visible blackheads more likely, especially on the nose, chin, and forehead where oil glands are already dense.
Where Blackheads Show Up Most
Blackheads cluster in areas where oil glands are largest and most concentrated. The forehead, nose, and chin (the T-zone) have far more oil glands per square centimeter than other parts of the face, which is why blackheads tend to appear there first. The chest, shoulders, and upper back also have high gland density, making them common sites for body blackheads. Areas with few oil glands, like the forearms and shins, almost never develop them.
How Diet Plays a Role
High-glycemic foods, those that cause rapid spikes in blood sugar like white bread, sugary drinks, and processed snacks, have been linked to higher rates of acne, including blackheads. These foods raise insulin levels, which in turn boosts androgen activity and sebum production. It’s the same hormonal chain that drives blackheads during puberty, just triggered by diet instead of developmental changes.
Switching to a lower-glycemic diet that emphasizes vegetables, whole grains, and fruit has helped some people reduce breakouts and inflammation. That said, this approach seems to work best in people who have underlying insulin sensitivity. It’s not a universal fix, but if you eat a lot of refined carbohydrates and struggle with persistent blackheads, it’s worth experimenting with.
Skincare Products That Clog Pores
Some ingredients in moisturizers, sunscreens, makeup, and even hair products are comedogenic, meaning they’re prone to clogging pores. Common offenders include certain waxes, heavy plant oils (like coconut oil), and lanolin-derived ingredients. These substances can sit inside the pore and mix with your skin’s own oil, accelerating plug formation.
Products labeled “non-comedogenic” are formulated to avoid these ingredients, though no universal standard governs that label. If you’re prone to blackheads, checking ingredient lists matters more than trusting front-of-package claims. Anything you apply to your face, hairline, or upper body can contribute, including conditioner that rinses down your back in the shower or heavy styling products that migrate onto your forehead.
Blackheads vs. Sebaceous Filaments
Many of the tiny dark dots on your nose aren’t actually blackheads. They’re sebaceous filaments, a normal part of your skin’s oil-delivery system. The difference matters because filaments don’t need treatment and can’t be permanently removed.
Blackheads are a form of acne. They appear as raised, dark bumps where a solid plug of oxidized oil blocks the pore. Sebaceous filaments are flat, smaller, and lighter in color, typically gray, light brown, or yellowish. They don’t have a plug. Instead, they’re simply the visible structure of oil as it moves through the pore toward the surface. If you squeeze a blackhead, a dark, waxy plug pops out. If you squeeze a sebaceous filament, a thin, threadlike strand of oil emerges, and the filament refills within about 30 days.
The nose is the most common spot where people mistake filaments for blackheads. If every pore on your nose looks roughly the same, evenly spaced and uniformly colored, you’re likely looking at filaments. True blackheads are more scattered and distinctly darker than the surrounding pores.
Other Contributing Factors
Anything that traps oil and dead skin against the surface can promote blackheads. Tight clothing, helmets, and backpack straps create friction and heat that increase oil production in the covered area. Humid environments make it harder for sweat and oil to evaporate, leaving more residue to settle into pores. Touching your face frequently transfers oils and bacteria from your hands.
Some medications increase blackhead risk as a side effect. Certain steroids, lithium, and some hormonal treatments can stimulate oil production or alter skin cell turnover. If blackheads appeared shortly after starting a new medication, that connection is worth exploring with your prescriber.