Pimples form when your skin’s oil glands produce too much oil, dead skin cells clog the pore, and bacteria multiply inside that blocked pore, triggering inflammation. But what drives that process in the first place varies from person to person. Hormones, diet, stress, genetics, physical friction, and even certain medications can all set the stage for breakouts.
How a Pimple Actually Forms
Every pimple starts in a tiny structure called a hair follicle, which is connected to an oil-producing gland just beneath the skin’s surface. Under normal conditions, oil travels up through the follicle and spreads across your skin to keep it moisturized. A pimple develops when four things happen in sequence.
First, the gland starts pumping out more oil than the pore can handle. Second, dead skin cells that normally shed and wash away instead stick together and form a plug at the opening of the follicle. Third, a bacterium called Cutibacterium acnes, which lives naturally on everyone’s skin, gets trapped behind that plug and multiplies rapidly in the oily, low-oxygen environment. Fourth, your immune system notices the bacterial overgrowth and sends inflammatory cells to fight it. That inflammation is what turns a clogged pore into a red, swollen, sometimes painful pimple.
The type of pimple you get depends on how deep the blockage sits and how much inflammation occurs. A shallow, non-inflamed clog produces a whitehead or blackhead. A deeper, more inflamed blockage creates papules, pustules, or the larger, more painful nodules and cysts that can leave scars.
Hormones Are the Biggest Driver
The oil glands in your skin are directly controlled by hormones called androgens, particularly a potent form of testosterone. Your skin actually converts testosterone into this stronger version right inside the oil gland itself, especially in glands on the face and scalp. When androgen levels rise, these glands grow larger and produce significantly more oil.
This is why acne follows a predictable life pattern. Oil gland activity first peaks in the first week after birth (due to hormones passed from the mother), then rises again around age 9 as the adrenal glands ramp up, and hits its highest point during the teenage years. Puberty floods the body with androgens, which is why nearly all teenagers deal with some degree of breakouts.
Hormonal acne doesn’t stop after puberty, though. Many adults, particularly women, experience breakouts tied to their menstrual cycle, pregnancy, polycystic ovary syndrome (PCOS), or the hormonal shifts of perimenopause. These breakouts tend to cluster along the jawline and chin, and they often appear as deeper, more tender bumps rather than surface-level whiteheads.
How Diet Feeds Into Breakouts
Two dietary patterns have the strongest links to acne: high-sugar foods and dairy.
Foods that spike your blood sugar quickly (white bread, sugary drinks, candy, processed snacks) cause your body to release a surge of insulin. That insulin boost raises levels of a growth hormone called IGF-1, which directly stimulates your oil glands to produce more sebum and promotes the kind of cell growth that clogs pores. In short, a diet heavy in refined carbs and sugar creates a hormonal environment inside your body that favors breakouts, even if you’re washing your face perfectly.
Dairy is more surprising. A large meta-analysis covering over 78,000 children, adolescents, and young adults found that any dairy consumption was associated with a 25% higher likelihood of acne compared to no dairy intake. Low-fat and skim milk showed the strongest association, with a 32% increase, while whole milk showed a 22% increase. One possible explanation: people who choose low-fat milk often drink more of it. Cheese and yogurt showed smaller but still measurable links. The mechanism likely involves the natural hormones and growth factors present in milk, which can amplify the same IGF-1 pathway that high-sugar foods trigger.
Stress Makes Existing Acne Worse
Stress doesn’t create acne from nothing, but it reliably makes existing breakouts worse. When you’re under psychological stress, your brain activates a cascade that ultimately increases cortisol and other stress hormones. One of those hormones, called corticotropin-releasing hormone (CRH), doesn’t just affect your brain. It also acts directly on oil glands in your skin, stimulating them to produce more oil and more inflammatory compounds.
Research has found that skin already affected by acne shows significantly higher levels of CRH in its oil glands compared to clear skin. This helps explain the frustrating cycle many people experience: stress triggers a flare-up, the flare-up causes more stress, and the breakouts keep coming. In adult women especially, chronic stress increases the secretion of adrenal androgens, which enlarges and activates oil glands in the same way puberty does.
Genetics Set Your Baseline Risk
If both your parents had acne, your chances of dealing with it are substantially higher. Twin studies have shown that up to 85% of the variation in acne severity between people can be attributed to genetic factors. That’s an enormous proportion, meaning the genes you inherit influence everything from how much oil your skin produces, to how readily your pores clog, to how aggressively your immune system reacts to blocked follicles.
This genetic component explains why some people can eat poorly, skip their skincare routine, and still have clear skin, while others do everything “right” and still break out. It also means that if you have a strong family history of acne, you may need to be more proactive about the factors you can control.
Physical Friction and Pressure
Anything that traps heat, sweat, and pressure against your skin can trigger localized breakouts, a condition dermatologists call acne mechanica. Common culprits include tight bra straps, backpack straps, helmets, hats, chin straps, football shoulder pads, and even the constant rubbing of a seatbelt. Truck drivers, for example, are known to develop breakouts on their backs from prolonged pressure against the seat.
The mechanism is straightforward: friction and pressure rupture tiny, invisible clogs (microcomedones) that already exist beneath the skin’s surface, turning them into inflamed pimples. Research has demonstrated that simply sealing acne-prone skin under an adhesive covering for two weeks consistently produces new inflammatory lesions from these ruptured microcomedones. If you notice breakouts that follow the exact outline of a strap, headband, or mask, friction is almost certainly the trigger.
Medications That Cause Breakouts
Several types of medications can trigger acne or acne-like eruptions as a side effect. The most common offenders are corticosteroids, both oral and topical. Steroid-induced breakouts look different from regular acne: they tend to appear as uniform small bumps concentrated on the chest, back, and arms rather than the face, and they typically show up shortly after starting the medication. Inhaled steroids can cause similar eruptions around the nose and mouth.
Other medications linked to breakouts include certain anticonvulsants, antidepressants, antipsychotics (particularly lithium), some antifungal drugs, and certain chemotherapy agents. If you started a new medication and noticed a sudden crop of pimples in an unusual pattern, the medication is worth investigating as the cause. These eruptions generally clear up after the medication is stopped or changed.
What You Can Actually Control
Given that genetics account for such a large share of acne risk, it helps to focus on the modifiable factors. Reducing your intake of high-glycemic foods and excess dairy may lower the hormonal signals that drive oil production. Managing stress through sleep, exercise, or other means can reduce the cortisol-driven flare-ups. Swapping out tight-fitting gear or wearing moisture-wicking layers under straps and helmets can prevent friction-related breakouts.
Keeping your skin clean matters, but less than most people think. Over-washing or scrubbing can actually irritate the skin and worsen inflammation. A gentle cleanser twice a day is generally sufficient for surface hygiene. The real drivers of pimples are happening beneath the skin’s surface, governed by hormones, genetics, and immune responses that no amount of face-washing can fully override.