Pimples form when hair follicles in your skin get clogged with oil and dead skin cells, creating a plug that traps bacteria and triggers inflammation. Your face is especially prone because it has more oil-producing glands per square inch than almost anywhere else on your body. Four biological processes drive every breakout: excess oil production, clogged pores, bacterial growth, and inflammation. But the reasons those processes kick into gear range from hormones and genetics to diet, stress, and even the air you breathe.
How a Pimple Actually Forms
Your skin is covered in tiny hair follicles, each paired with an oil gland that produces sebum, a waxy substance that keeps skin lubricated. Normally, sebum travels up the follicle and spreads across the skin’s surface. Problems start when your body produces too much sebum or when dead skin cells don’t shed properly. Instead of sloughing off, those cells mix with excess oil and form a plug inside the follicle.
That plug creates a sealed, oxygen-poor environment where bacteria thrive. One species in particular, called C. acnes, lives naturally on everyone’s skin but multiplies rapidly inside blocked pores. Different strains of this bacterium trigger different levels of immune response. Strains associated with acne-prone skin produce sugar molecules on their surface that provoke your immune system into releasing inflammatory signals. Your body sends white blood cells to fight the bacteria, and the result is the redness, swelling, and pus you see as a pimple. When this battle happens deep below the surface, it can produce painful, cyst-like lumps.
Hormones Are the Biggest Driver
Hormones called androgens are the single most important trigger for excess oil production. Androgens, especially a potent form called dihydrotestosterone (DHT), bind to receptors on your oil glands and essentially flip a switch that tells those glands to grow larger and produce more sebum. Research has shown this relationship is so direct that people who lack functioning androgen receptors don’t produce sebum at all and never develop acne.
This is why pimples are so common during puberty, when androgen levels surge in both boys and girls. But hormonal acne isn’t limited to teenagers. Women often experience breakouts tied to their menstrual cycle, pregnancy, or polycystic ovary syndrome, all of which involve shifts in androgen levels. Hormonal pimples tend to cluster along the jawline and lower face, though they can appear anywhere.
Genetics Play a Larger Role Than You’d Think
If your parents had acne, your chances of dealing with it are significantly higher. Twin studies in Australian adolescents found that about 85% of the variation in acne severity is explained by genetics. That leaves only about 15% attributable to environmental and lifestyle factors. Your genes influence how much oil your skin produces, how quickly your skin cells turn over, how sensitive your oil glands are to hormones, and how aggressively your immune system responds to clogged pores. You can’t change your genetic blueprint, but knowing that acne runs in your family helps explain why some people break out despite doing everything “right.”
What Your Diet Does (and Doesn’t) Do
Two dietary patterns have the strongest links to breakouts: dairy and high-sugar foods. Milk and dairy products contain proteins (casein and whey) that raise levels of a hormone called IGF-1 in your blood. People with acne tend to have higher IGF-1 levels than people without it, and IGF-1 directly stimulates oil glands to ramp up production. Dairy also naturally contains hormones, including androgens, that can add to the problem.
Foods that spike your blood sugar quickly, like white bread, sugary drinks, and processed snacks, may also play a role. In controlled trials, people who switched to a low-glycemic diet (one that keeps blood sugar more stable) saw their total pimple count decrease compared to those eating high-sugar diets. That said, the overall evidence linking high-glycemic diets to acne is still considered modest, and individual responses vary. Chocolate, greasy food, and other classic suspects have never been convincingly proven to cause breakouts on their own.
How Stress Gets Under Your Skin
Stress doesn’t just make existing pimples feel worse. It actively fuels the biological processes behind them. When you’re stressed, your body activates a hormonal cascade that releases cortisol and other stress hormones. Your skin cells have their own receptors for these hormones and can even produce them locally, creating a feedback loop of inflammation right where breakouts happen.
Stress also triggers nerve endings in the skin to release neuropeptides, small signaling molecules that amplify immune responses and increase oil production. This is why you might notice breakouts during exam weeks, job changes, or periods of poor sleep. The pimples aren’t coincidental. They’re a measurable biological response to psychological pressure.
Air Pollution and Environmental Factors
If you live in a city or near heavy traffic, the air itself may be contributing to your breakouts. Airborne particulate matter (tiny particles from vehicle exhaust, industrial emissions, and dust) settles on your skin and disrupts the skin barrier. Research has found that pollution exposure promotes sebum production while simultaneously depleting protective antioxidants like vitamin E from the skin’s surface. It also alters the chemical composition of your sebum, making it more likely to clog pores and trigger inflammation.
Humidity and heat compound the problem by increasing sweat production and creating a film on the skin that traps pollutants against your pores. Even friction from phone screens, helmets, or face masks can cause localized breakouts by pressing oil and bacteria into the skin.
Medications That Cause Breakouts
Certain medications can trigger acne or make existing breakouts significantly worse. The most common culprits include:
- Corticosteroids: Whether taken as pills, inhaled for asthma, or applied in large amounts as creams, these frequently cause acne-like eruptions.
- Testosterone and anabolic steroids: About 50% of people who use anabolic steroids in high doses develop acne as a side effect.
- Lithium: Used for mood disorders, long-term lithium therapy commonly causes skin problems including acne.
- B12 supplements: High doses (5 to 10 mg per week) have been linked to breakouts.
- Certain birth control pills: Older-generation progestins like levonorgestrel have androgen-like effects that can increase oil production.
- Some cancer treatments: A class of drugs that target a growth receptor on cells causes acne-like rashes in roughly 85% of patients.
Drug-induced acne typically looks slightly different from regular acne. It often appears suddenly, affects areas beyond the face (like the chest and back), and the pimples tend to be more uniform in size. If your breakouts started or worsened after beginning a new medication, that connection is worth exploring with whoever prescribed it.
Pore-Clogging Products and Skincare Habits
Heavy moisturizers, foundations, sunscreens, and hair products can physically block your pores, especially along the forehead and hairline. Products labeled “non-comedogenic” are formulated to avoid this, though the term isn’t regulated and doesn’t guarantee you won’t react. Oil-based makeup removers, coconut oil, and thick leave-in conditioners are frequent offenders.
Overwashing your face can also backfire. Scrubbing aggressively or washing more than twice a day strips your skin’s natural moisture barrier, which triggers your oil glands to compensate by producing even more sebum. The same rebound effect happens when you use harsh astringents or alcohol-based toners. A gentle cleanser used morning and night is typically more effective than aggressive washing.
Why Pimples Favor Certain Areas of the Face
The T-zone (forehead, nose, and chin) has the highest concentration of oil glands on the face, which is why these areas tend to break out first and most often. The cheeks have fewer oil glands but are more exposed to external factors like phone screens, pillowcases, and hands touching the face. Jawline and lower-face acne is more commonly driven by hormonal fluctuations, particularly in women over 25. Hairline breakouts often point to product buildup from shampoo, conditioner, or styling products that migrate onto the skin.
Where your pimples consistently appear can offer useful clues about what’s driving them, even if the underlying biology of clogged pores and inflammation is the same everywhere on your face.