Acne develops when oil and dead skin cells clog your hair follicles, creating an environment where bacteria thrive and trigger inflammation. That’s the short answer, but the reason you specifically keep breaking out depends on a combination of hormones, genetics, stress, diet, and even the particular bacteria living on your skin. Understanding which factors are driving your acne helps explain why it showed up when it did and why certain areas of your face or body are affected more than others.
The Four Processes Behind Every Breakout
Every pimple, blackhead, or cyst traces back to the same chain of events happening inside a hair follicle. First, your oil glands produce too much sebum, the waxy substance that normally keeps skin moisturized. Second, dead skin cells that should shed naturally instead stick together and form a plug at the follicle’s opening. Third, bacteria that normally live harmlessly on your skin get trapped behind that plug and multiply. Fourth, your immune system responds to the bacterial overgrowth with inflammation, producing the redness, swelling, and pain you see on the surface.
These four factors don’t carry equal weight for everyone. Some people overproduce oil but rarely get inflamed cysts. Others have relatively normal oil levels but shed skin cells in a way that constantly blocks pores. Your particular combination determines whether you get scattered blackheads, deep painful nodules, or something in between.
How Hormones Control Your Oil Glands
Androgens, a group of hormones that includes testosterone, are the primary signal telling your oil glands to ramp up production. Your skin doesn’t just respond passively to hormones circulating in your blood. It actively converts weaker hormones into more potent forms right inside the oil gland itself. Your skin contains all the enzymes needed to transform a weak precursor hormone into a powerful form that directly stimulates oil production.
One enzyme in particular is found at higher levels in skin that’s prone to acne compared to skin in areas that rarely break out. This helps explain why acne clusters on your face, chest, and upper back rather than, say, your forearms. Those acne-prone zones have oil glands that are especially responsive to hormonal signals.
This hormonal mechanism is why acne so often appears during puberty, when androgen levels surge. But it also explains breakouts tied to menstrual cycles, pregnancy, polycystic ovary syndrome (PCOS), and menopause. Any shift in your hormonal balance can change how much oil your skin produces.
Teen Acne vs. Adult Acne
If you’re a teenager, your acne is likely driven by the dramatic rise in androgens during puberty. These hormones push oil glands into overdrive, which is why teen breakouts tend to concentrate in the T-zone (forehead, nose, and chin) as well as the back, chest, and shoulders. These areas have the highest density of oil glands.
Adult acne, especially in women, follows a different pattern. Breakouts tend to cluster along the jawline, chin, around the mouth, and sometimes the neck. This distribution is often called “hormonal acne” because it maps onto the areas most sensitive to hormonal fluctuations from menstrual cycles, pregnancy, or conditions like PCOS and thyroid disorders. If your acne appeared or worsened well past your teenage years and sits primarily on your lower face, fluctuating hormones are the most likely driver.
Stress Makes It Worse for a Specific Reason
The link between stress and breakouts isn’t just anecdotal. When you’re stressed, your body produces corticotropin-releasing hormone (CRH) and cortisol. Both of these directly affect your oil glands. Research has found significantly stronger expression of CRH in the oil glands of acne-affected skin compared to clear skin.
CRH does something counterintuitive: it actually slows down the growth of oil gland cells while simultaneously increasing how much oil each cell produces. It also activates enzymes that convert weaker hormones into androgens right at the skin level. So stress doesn’t just make you feel lousy. It chemically reprograms your oil glands to produce more sebum and amplifies the same hormonal pathway that drives acne in the first place.
What Your Diet Is Doing to Your Skin
Two dietary patterns have the strongest evidence linking them to acne: high-glycemic foods and dairy.
When you eat foods that spike your blood sugar quickly (white bread, sugary drinks, processed snacks), your body releases a surge of insulin. That insulin triggers a cascade that increases levels of a growth factor called IGF-1. Elevated IGF-1 stimulates your oil glands, promotes the growth of oil-producing cells, and encourages the kind of pore-clogging that leads to comedones (the technical term for clogged pores that become blackheads and whiteheads). In short, a diet heavy in refined carbohydrates and sugar doesn’t just affect your waistline. It feeds the biological machinery of acne.
Dairy tells a similar story. A meta-analysis of observational studies found that people with the highest dairy intake were more than twice as likely to have acne compared to those with the lowest intake. Skim milk showed a particularly strong association, with an 82% increased likelihood of acne. Whole milk and low-fat milk also correlated with breakouts, but less dramatically. The proteins in milk, casein and whey, raise insulin and IGF-1 levels, which loop back into the same oil-production and pore-clogging pathway triggered by high-sugar foods.
This doesn’t mean dairy or sugar cause acne in everyone, but if you’re already prone to breakouts, these foods can amplify the process.
Not All Skin Bacteria Are the Same
The bacterium most associated with acne lives on virtually everyone’s skin. It’s a normal part of your skin’s ecosystem. So the question isn’t whether you have it. The question is which strains you have and what they’re doing.
Genetic sequencing has revealed that certain strain types are far more common on acne lesions, while other strains are more frequently found on healthy, clear skin. The difference between an inflammation-triggering strain and a harmless one can come down to a single piece of genetic material: a small, circular segment of DNA called a plasmid. Strains carrying this plasmid provoke a much stronger inflammatory response from your immune system. Two people can carry the same species of bacteria on their face, but if one person’s strain carries that plasmid, their skin reacts with redness and swelling while the other person’s skin stays calm.
This is one reason acne isn’t simply a hygiene problem. Washing your face more aggressively won’t change which bacterial strains colonize your skin, and scrubbing too hard can actually damage the skin barrier and worsen inflammation.
Other Factors That Contribute
Genetics play a substantial role. If both of your parents had acne, your risk is significantly higher. Genes influence how large your oil glands are, how your immune system responds to bacteria, and how readily your skin cells shed or stick together.
Certain medications can trigger or worsen breakouts, particularly those containing corticosteroids, lithium, or certain hormonal treatments. Friction and pressure on the skin from helmets, tight clothing, or phone screens pressed against your face can also cause localized breakouts, sometimes called “acne mechanica.”
Cosmetic and skincare products that are oil-based or comedogenic (meaning they tend to block pores) can contribute as well. If your breakouts cluster in areas where you apply specific products, that’s worth investigating. Switching to non-comedogenic formulations sometimes resolves the problem entirely.
Why It Persists in Some People
Acne often isn’t a single-cause problem, which is why it can be so frustrating. You might have a genetic predisposition to overactive oil glands, made worse by hormonal fluctuations, compounded by a diet that spikes your IGF-1 levels, and topped off by stress that further amplifies oil production. Each factor alone might not be enough to cause persistent breakouts, but together they push your skin past its tipping point.
This layered nature also explains why a single change (cutting out dairy, reducing stress, switching face wash) sometimes helps but rarely eliminates acne completely on its own. The most effective approaches typically address multiple contributing factors at once.