What Causes Acne? | The Biology Behind Breakouts

Acne forms when hair follicles clog with oil and dead skin cells, then bacteria and inflammation worsen the lesion.

Few skin conditions inspire as much myth-making as acne. You’ve probably heard that chocolate causes it, or that dirty skin is to blame. The truth is more biological and less moralizing. Acne vulgaris — the common form that sends most people to the drugstore aisle — develops through a specific chain of events inside the pore. Understanding that chain won’t clear your skin overnight, but it will tell you which treatments actually matter and which old wives’ tales you can drop for good.

The Four-Step Process Inside A Pore

Every pimple follows the same basic sequence. First, your sebaceous glands produce too much sebum, the natural oil that normally keeps skin lubricated. Second, dead skin cells that should shed away instead stick together and mix with that excess oil. Third, the combination plugs the follicle opening. Finally, bacteria that normally live harmlessly on skin — especially Cutibacterium acnes, formerly called Propionibacterium acnes — multiply inside the blocked pore and trigger inflammation.

That inflammation is what turns a tiny plug into a red, tender pimple. The depth of the blockage determines the type of lesion: blackheads and whiteheads sit near the surface, while nodules and cysts form deeper and hurt more.

The Main Triggers: Hormones, Genetics, And More

Hormones lead the list of culprits. Androgens — hormones that rise during puberty in both boys and girls — enlarge sebaceous glands and boost oil production. That’s why acne peaks in the teen years, though adults get it too. Pregnancy shifts hormones enough to trigger breakouts in some women, and endocrine conditions like polycystic ovary syndrome can raise androgen levels and cause acne.

Genetics matter just as much. If your parents had acne, you’re more likely to have it; the National Institute of Arthritis and Musculoskeletal and Skin Diseases notes that family history is a significant contributor. Certain medications also provoke breakouts, including corticosteroids, lithium, some anticonvulsants, anabolic steroids, and some oral contraceptives.

What Makes Acne Worse (But Doesn’t Cause It)

Here’s where the myths die. Stress and diet do not cause acne, but both can worsen existing breakouts. The Mayo Clinic reports that some research ties high-glycemic-load diets — think white bread, sugary drinks — and cow’s milk or skim milk to more frequent or severe acne. Smoking may also contribute, especially in older adults.

Physical friction causes a specific type called acne mechanica. Helmets, headbands, backpacks, shoulder pads, and bra straps pressing and rubbing against skin can trigger or aggravate breakouts. Oil-based cosmetics can clog follicles too, though modern non-comedogenic products are tested to avoid this, making makeup a less common culprit than it once was.

One belief worth burying: acne is not caused by poor hygiene. Scrubbing harder won’t help and can irritate skin further. The blockage happens beneath the surface, not because you skipped a wash.

When Acne Signals Something Medical

Since acne is multifactorial, its causes vary person to person. But sudden, severe, or hormonal acne — especially in adult women — can point to an underlying condition worth a doctor’s visit. Mayo Clinic advises that acne appearing alongside other symptoms may need medical evaluation, particularly if over-the-counter products aren’t working after several weeks.

For most people, the standard routine holds: gentle cleansing, non-comedogenic moisturizer, and ingredients backed by dermatology. If you’re ready to upgrade your routine, our roundup of the best acne skin care products breaks down what actually earns its shelf space. When home care isn’t enough, a dermatologist can prescribe treatments targeting each step — from reducing oil to killing bacteria to calming inflammation. If your acne is sudden, severe, or accompanied by other symptoms, the Mayo Clinic’s guide on acne causes offers guidance on when to seek medical advice.