Acne develops when hair follicles in your skin become clogged with oil and dead skin cells, then get inflamed. But the reason *your* skin keeps breaking out comes down to a combination of factors: your genetics, your hormones, the bacteria living on your skin, and a range of everyday triggers you may not have considered. About 80% of your susceptibility to acne is inherited, which means the foundation was set before you ever washed your face or tried a new moisturizer. The good news is that understanding what drives acne gives you real leverage over it.
The Four Things Happening Inside a Breakout
Every pimple starts with the same chain of events inside a tiny structure called a pilosebaceous follicle, which is basically a hair follicle paired with an oil gland. Four processes converge to create a breakout: your oil glands produce too much sebum, dead skin cells build up and block the follicle opening, a specific type of bacteria flourishes in that clogged environment, and your immune system launches an inflammatory response. All four of these factors feed into each other. Excess oil gives bacteria more fuel. A blocked pore traps both the oil and the bacteria. And inflammation is what turns an invisible clog into a red, swollen bump you can see and feel.
Hormones Are Usually the Biggest Driver
Your oil glands are essentially hormone-responsive organs. Androgens, the group of hormones that includes testosterone, directly stimulate them to produce more sebum. Testosterone gets converted into a more potent form right inside your skin cells by an enzyme called 5-alpha reductase. That converted form binds to receptors in your oil glands with ten times the strength of regular testosterone, which is why even modest hormonal shifts can cause noticeable changes in your skin.
This is why acne so often shows up during puberty: a growth-related hormone called IGF-1 surges during adolescence and ramps up both androgen production and the activity of those converting enzymes. But hormonal acne doesn’t end with your teenage years. Roughly one in three women in their 30s still has acne, and hormonal fluctuations around menstrual cycles, pregnancy, or polycystic ovary syndrome keep oil glands active well into adulthood. Adult female acne tends to concentrate on the chin and jawline, which is a slightly different pattern than the more widespread breakouts of adolescence.
Your Skin Bacteria Matter More Than You Think
For years, the assumption was that acne came from having too much of the bacterium Cutibacterium acnes (formerly called Propionibacterium acnes) on your skin. That understanding has shifted. Everyone has C. acnes on their skin, including people with perfectly clear complexions. The difference is diversity. People with acne tend to be dominated by a single, more aggressive strain of C. acnes, while people without acne carry a wider variety of strains that keep each other in check.
When one strain takes over, it triggers your innate immune system to react, creating the redness and swelling of inflammatory acne. This helps explain why aggressively sterilizing your skin with harsh cleansers can backfire. Wiping out the broader bacterial community can actually make the imbalance worse.
What Your Diet Does to Your Skin
Foods that cause a rapid spike in blood sugar, like white bread, sugary drinks, and processed snacks, raise your insulin levels. Elevated insulin increases circulating IGF-1, which does two things that promote acne: it boosts androgen activity (pushing your oil glands to produce more sebum) and it ramps up the production of inflammatory signals directly inside your oil gland cells. Lab studies show that IGF-1 activates a specific inflammatory pathway in oil-producing cells, increasing markers of inflammation and fat production at the same time.
This doesn’t mean a single cookie causes a breakout. It means a consistently high-glycemic diet creates a hormonal environment that favors acne. Shifting toward lower-glycemic foods like whole grains, vegetables, and legumes can meaningfully reduce that hormonal pressure on your skin over weeks to months.
Stress Creates a Real Biological Effect
Stress acne isn’t imagined. When you’re under chronic stress, your body produces more cortisol, which directly increases oil gland activity and sebum output. Your skin cells also have their own local stress response system. They produce a stress hormone called CRH, which stimulates oil glands independently of what’s happening in the rest of your body. So even if your overall cortisol levels aren’t dramatically elevated, your skin can still be reacting to stress signals locally. This is why breakouts often cluster around exams, work deadlines, or emotionally difficult periods.
Products That Clog Your Pores
Some skincare and cosmetic ingredients physically block follicle openings, creating the same kind of plug that starts the acne cascade. This is sometimes called acne cosmetica. Common offenders include coconut oil, olive oil, palm oil, sesame oil, lanolin, and avocado butter. These show up in moisturizers, hair products, sunscreens, and foundations. If you’re breaking out in areas where you apply a specific product, the ingredient list is worth checking. Look for the term “non-comedogenic” on labels, which means the product has been formulated to avoid pore-clogging ingredients. Hair products like pomades and oils are a frequently overlooked cause of forehead and hairline breakouts.
Medications That Trigger Breakouts
Certain medications can cause acne or acne-like eruptions as a side effect. Corticosteroids are among the most common culprits, particularly at high doses or when given intravenously. These tend to produce breakouts concentrated on the chest and back rather than the face. Other medications linked to acneiform eruptions include lithium, vitamin B12, thyroid hormones, certain antiepileptic drugs, and some antibiotics. If your acne appeared or worsened shortly after starting a new medication, that timing is worth noting and discussing with whoever prescribed it.
Pollution and Your Skin Barrier
Air pollution contributes to acne in a less obvious way. Particulate matter and compounds called polycyclic aromatic hydrocarbons, which are common in urban air pollution, trigger inflammatory responses in your skin. Over time, this exposure depletes your skin’s natural antioxidant defenses, including vitamins C and E, creating a low-grade inflammatory environment and weakening your skin barrier. A compromised barrier is more vulnerable to the clogging and bacterial imbalance that lead to breakouts. If you live in a city with heavy traffic or industrial pollution, this background inflammation may be compounding other acne triggers.
Genetics Set the Stage
Twin studies consistently estimate acne heritability at around 80%. That means the size of your oil glands, how your skin cells shed inside follicles, how your immune system responds to C. acnes bacteria, and how sensitive your oil glands are to hormones are all heavily influenced by the genes you inherited. If both of your parents had acne, your odds of dealing with it are substantially higher. Genetics also influence where you break out, how severe your acne gets, and how long it persists into adulthood. You can’t change your genetic predisposition, but recognizing it helps you focus on the modifiable triggers, like diet, stress, product choices, and skincare routine, where you actually have control.