Blackheads form when a pore becomes clogged with a mix of oil and dead skin cells, and the surface of that plug is exposed to air. The dark color isn’t dirt. It’s the result of oxidation, the same chemical reaction that turns a sliced apple brown. About 85% of people between ages 12 and 24 experience some form of acne, and blackheads are one of the most common types.
Understanding what’s actually happening inside the pore helps explain why blackheads keep coming back and what makes some people more prone to them than others.
What Happens Inside the Pore
Every pore on your skin contains a hair follicle and an oil gland. The oil gland produces sebum, a waxy substance that keeps your skin moisturized. Normally, sebum travels up through the pore and spreads across the skin’s surface without any issues.
A blackhead starts forming when the cells lining the inside of the pore begin behaving abnormally. Instead of shedding and clearing out in an orderly way, these cells multiply too fast and stick together. This creates a plug of dead skin and oil that partially blocks the pore opening. Because the pore stays open at the surface (unlike a whitehead, which is sealed over), the material inside is exposed to oxygen. That exposure triggers oxidation of the pigment melanin in the plug, turning it dark brown or black.
This is a key distinction: the black color comes from a chemical reaction, not from trapped dirt. Blackheads are not a sign of poor hygiene, and aggressive scrubbing won’t prevent them. In fact, harsh scrubbing can damage skin and increase inflammation, potentially making breakouts worse.
Hormones Are the Primary Driver
The biggest factor behind blackhead formation is hormonal. Androgens, particularly testosterone and its more potent form DHT, directly stimulate oil glands to produce more sebum. Androgen receptors sit right at the base of the oil gland, so when hormone levels rise, sebum production ramps up quickly.
This is why blackheads often first appear during puberty, when androgen levels surge. It’s also why hormonal fluctuations during menstrual cycles, pregnancy, or polycystic ovary syndrome can trigger new breakouts in adults. Up to 15% of adult women deal with ongoing acne, often driven by these hormonal shifts. Your oil glands can even produce their own androgens locally from a precursor hormone made by the adrenal glands, which means hormonal activity at the skin level doesn’t always mirror what’s happening in your bloodstream.
Excess Oil Production
Some people simply produce more sebum than others, regardless of their hormone levels. Genetics play a significant role here. If your parents had oily skin or struggled with blackheads, you’re more likely to as well. Oilier skin means more raw material available to clog pores, and areas with the highest concentration of oil glands (the nose, forehead, and chin) are where blackheads tend to cluster.
Environmental factors matter too. Hot, humid weather increases oil production. So does over-washing your face with harsh cleansers, which strips the skin and triggers a rebound effect where oil glands compensate by producing even more sebum.
Products That Clog Pores
Certain ingredients in skincare, makeup, and hair products are comedogenic, meaning they physically block pores and promote blackhead formation. Common culprits include acetylated lanolin alcohol (found in many moisturizers), certain waxes, and heavy plant-based oils. These ingredients can sit inside the pore and act like glue, trapping dead skin cells and sebum together.
Labels claiming “noncomedogenic,” “oil-free,” or “won’t clog pores” aren’t always reliable. These terms aren’t regulated in any standardized way, so a product can carry those claims while still containing pore-clogging ingredients. The inherent nature of the ingredient doesn’t change based on how it’s formulated into a product. If you’re prone to blackheads, checking individual ingredient lists matters more than trusting front-of-bottle marketing.
Diet and Blackheads
There’s a widely held belief that high-sugar diets and dairy consumption worsen acne. The theory has biological logic: foods with a high glycemic load spike insulin and a growth hormone called IGF-1, both of which can stimulate oil production and skin cell turnover. Dairy contains its own hormones that could theoretically do the same.
However, the clinical evidence is surprisingly weak. A systematic review pooling data from multiple studies found no statistically significant link between glycemic load, dairy intake, or fatty acid profiles and acne severity. That doesn’t mean diet has zero effect on your skin, but the connection is far less clear-cut than social media and wellness culture suggest. Hormones, genetics, and skincare habits have a much stronger and more consistent relationship with blackhead formation.
Medications That Trigger Breakouts
Certain medications can cause or worsen comedonal acne as a side effect. Lithium, commonly prescribed for bipolar disorder, is one of the better-documented examples. Studies have found acne-like eruptions in about 33% of patients on lithium, compared to just 9% of patients with similar mood disorders who weren’t taking the drug. Corticosteroids, some anticonvulsants, and certain hormonal medications can also increase oil production or alter how skin cells behave inside the pore.
If you notice a sudden increase in blackheads after starting a new medication, the timing is worth paying attention to.
Blackheads vs. Sebaceous Filaments
Many people think they have blackheads on their nose when what they’re actually seeing are sebaceous filaments. These are a normal part of skin anatomy, not a form of acne. The difference matters because it changes what you should do about them.
Blackheads are raised, dark-colored bumps where a plug of oil and dead skin physically blocks the pore. If you were to extract one (not recommended regularly), a dark, waxy plug would come out. Sebaceous filaments, on the other hand, are flat, smaller, and lighter in color, typically gray, yellowish, or light brown. They don’t contain a plug. Oil flows freely through the pore, and if you squeeze one, a thin, thread-like strand of wax emerges rather than a solid mass.
Sebaceous filaments are most visible on the nose, forehead, chin, and cheeks, exactly where people tend to worry about blackheads. They’re present on everyone’s skin and will refill within about 30 days if extracted. Trying to remove them aggressively can irritate the skin and enlarge pores over time, making them even more noticeable.
Why Some People Get More Blackheads
Blackhead formation comes down to a combination of factors working together. Larger pore size (largely genetic), higher sebum production (driven by hormones and genetics), and how quickly your skin cells turn over all influence whether a pore stays clear or gets blocked. Someone with naturally oily skin going through a hormonal shift while using a heavy moisturizer is stacking multiple risk factors at once.
Age plays a role too. Blackheads are most common during adolescence and early adulthood, when hormonal activity peaks. But they can persist well into the 30s and 40s, particularly in women experiencing hormonal changes. The American Academy of Dermatology notes that acne can occur at any stage of life, and a one-size-fits-all approach rarely works because the underlying causes vary from person to person.