Blackheads form when a pore fills with a mix of oil and dead skin cells, and the surface of that plug is exposed to air. The exposure triggers a chemical reaction called oxidation, which turns the plug dark brown or black. Despite what many people assume, the dark color isn’t dirt.
What Happens Inside the Pore
Every hair follicle on your skin sits inside a tiny structure that includes an oil-producing gland. This gland constantly makes sebum, a waxy, oily substance that keeps your skin moisturized and protected. Normally, sebum travels up through the pore and spreads across the skin’s surface without issue.
A blackhead starts forming when something disrupts that flow. The cells lining the inside of the pore begin to shed abnormally, clumping together instead of exiting smoothly. These sticky dead cells mix with sebum and create a physical plug near the top of the pore. At this stage, the clog is microscopic and invisible to the naked eye. Dermatologists call it a microcomedo, and it’s the precursor to every blackhead, whitehead, and most other forms of acne.
What makes a blackhead different from a whitehead is simple geometry. In a blackhead, the pore stays open at the surface. The plug sits right at the top, exposed to air. In a whitehead, a thin layer of skin closes over the pore, sealing the plug underneath. That’s the only structural difference between the two.
Why Blackheads Look Black
Sebum contains traces of melanin (the same pigment that colors your skin and hair) along with certain fatty molecules. When this mixture sits at the surface of an open pore, it reacts with oxygen in a process called oxidation. The reaction darkens the plug progressively, turning it yellow, brown, or eventually black. The longer the buildup sits exposed, the darker it gets, because the pore isn’t cleaning itself out and the material continues to oxidize.
This is the same basic chemistry that turns a sliced apple brown. It has nothing to do with hygiene or how clean your face is.
What Drives Excess Oil Production
The single biggest factor behind blackheads is how much oil your skin produces, and that’s largely controlled by hormones. Androgens, a group of hormones that includes testosterone, directly stimulate oil glands to ramp up production. Your oil glands can actually convert testosterone into a more potent form that further increases oil output. This is why blackheads so often appear during puberty, menstrual cycles, and other periods of hormonal change.
Hormones aren’t the only signal. Insulin and a related growth factor called IGF-1 also push oil glands to produce more sebum. High-glycemic diets (think white bread, sugary drinks, processed snacks) spike insulin levels, which in turn raise IGF-1. Clinical research has confirmed that these elevated levels stimulate both sebum production and androgen release, creating a double hit that promotes clogged pores. Stress hormones play a role too: cortisol-related signaling pathways in the skin can independently boost oil output.
Other Factors That Clog Pores
Certain skincare and cosmetic ingredients are comedogenic, meaning they’re known to block pores. The list is long and includes compounds like acetylated lanolin alcohol (common in moisturizers), various waxes, and some seaweed-derived thickeners. “Non-comedogenic” on a label means the product was formulated to avoid these ingredients, though the term isn’t regulated, so checking ingredient lists yourself is more reliable than trusting marketing claims.
Physical factors matter as well. Anything that traps heat and moisture against your skin, like tight helmets, headbands, or phone screens pressed against your chin, can accelerate the buildup inside pores. Humid environments increase oil production on their own. And while washing your face removes surface oil, overwashing can irritate the skin and trigger a rebound increase in sebum, making the problem worse rather than better.
Blackheads vs. Sebaceous Filaments
Many of the tiny dark dots on your nose aren’t blackheads at all. They’re sebaceous filaments, which are a completely normal part of how your skin functions. The difference is important because it determines whether treatment is useful or a waste of time.
Blackheads are raised bumps with a dark, firm plug that blocks the pore entirely. If you were to extract one, a dark, waxy ball would pop out. Sebaceous filaments are flat, smaller, and lighter in color, typically gray, light brown, or yellowish. They don’t have a plug, so oil still flows freely through the pore. Squeezing one produces a thin, thread-like strand rather than a solid ball. Sebaceous filaments refill within about 30 days no matter what you do, so extracting them is pointless. If the dots on your nose are uniformly spaced, light-colored, and flat, you’re looking at normal skin architecture, not acne.
How Blackheads Are Treated
Because the plug in a blackhead is made of oil and dead skin cells, treatment targets one or both of those components.
Salicylic acid is the most widely used over-the-counter option. It’s oil-soluble, so it can penetrate into the pore and help dissolve the plug from the inside. Cleveland Clinic recommends starting with a product containing 2% to 4% salicylic acid. Consistency matters more than strength: using a lower concentration daily is generally more effective than using a high concentration occasionally.
Retinoids work differently. Instead of dissolving existing plugs, they change how the cells lining the pore behave. Tretinoin, the most studied topical retinoid, alters the environment inside the pore and normalizes the shedding of skin cells, which is the root cause of the blockage. This makes retinoids especially useful for preventing new blackheads from forming, not just clearing existing ones. Over-the-counter retinol is a milder version of the same approach, while prescription-strength retinoids work faster.
Manual extraction, where a dermatologist or esthetician uses a small metal tool to press the plug out, gives immediate results but doesn’t change the underlying process. Without ongoing treatment to control oil and cell turnover, the pore will refill. Pore strips work on the same principle: they physically pull surface plugs out, but the effect is temporary.
Why Some People Get More Blackheads
Genetics largely determine the size of your pores and how active your oil glands are. If your parents had oily skin, you’re more likely to produce excess sebum. Larger pores are also more visible when clogged, which is why blackheads concentrate on the nose, chin, and forehead, where pores tend to be biggest and oil glands most dense.
Age plays a role in both directions. Blackheads peak during adolescence when androgen levels surge, but they can persist well into adulthood, especially in people whose hormonal balance continues to fluctuate. Some adults who never had acne as teenagers develop blackheads later, often related to hormonal shifts, dietary changes, or new skincare products that happen to be comedogenic.