Pimples form when a hair follicle gets clogged with oil and dead skin cells, then becomes inflamed. It sounds simple, but several processes have to go wrong at once: your skin overproduces oil, dead cells stick together instead of shedding normally, bacteria multiply inside the blocked pore, and your immune system reacts. Understanding each of these steps helps explain why breakouts happen and what actually makes them worse.
The Four Things That Create a Pimple
Every pimple starts with the same basic chain of events. First, the cells lining a hair follicle begin multiplying faster than normal and stop shedding the way they should. Instead of flaking off and clearing out, they clump together and form a tiny plug deep inside the pore. This microscopic blockage, called a microcomedone, is invisible to the naked eye but serves as the seed for every type of acne lesion that follows.
Second, your oil glands pump out more sebum than the pore can handle. That oil backs up behind the plug, expanding the follicle like a water balloon. Third, a bacterium called C. acnes, which normally lives on everyone’s skin in small numbers, thrives in this oxygen-poor, oil-rich environment and multiplies rapidly. Fourth, your immune system detects the bacterial overgrowth and launches an inflammatory response. White blood cells flood the area, and the follicle wall can rupture, spreading inflammation into the surrounding skin. That’s when a blocked pore turns into a red, swollen, painful bump.
Why Your Oil Glands Go Into Overdrive
Hormones are the primary driver of excess oil production, which is why acne peaks during puberty and flares around menstrual cycles. Androgens, particularly testosterone and its more potent form dihydrotestosterone (DHT), directly stimulate oil glands to grow larger and produce more sebum. Studies on prepubescent boys given testosterone showed both increased sebum output and visibly enlarged oil glands. Your oil glands can even manufacture their own androgens locally from a precursor hormone produced by the adrenal glands, which means hormonal acne isn’t always tied to abnormal blood hormone levels.
Growth hormone and insulin-like growth factor 1 (IGF-1) also play a role. Elevated IGF-1 stimulates oil glands to ramp up fat production through a specific signaling pathway. This connection is part of why diet can influence breakouts, which we’ll get to shortly.
Genetics Play a Bigger Role Than You Think
If your parents had acne, your chances of getting it are high. Twin studies estimate that about 85% of the variation in acne severity is explained by genetics. That leaves only about 15% attributable to environmental factors. Your genes influence how much oil your skin produces, how your follicles shed dead cells, how aggressively your immune system responds to clogged pores, and how sensitive your oil glands are to hormones. This is why some people can use the same products and eat the same diet as a friend yet have completely different skin.
How Diet Affects Breakouts
The connection between food and acne centers on insulin and IGF-1. High-glycemic foods (white bread, sugary drinks, processed snacks) cause a rapid spike in blood sugar, which triggers a surge of insulin. Insulin raises IGF-1 levels, and elevated IGF-1 directly stimulates oil glands to produce more sebum. Several studies have found that higher serum IGF-1 levels correlate with both increased oil production and worse acne.
Dairy, particularly skim milk, has also been linked to breakouts in observational studies, possibly because milk naturally contains hormones and growth factors that influence oil production. This doesn’t mean a single slice of pizza causes a pimple. But a consistently high-glycemic diet can create a hormonal environment that keeps your oil glands working overtime.
Friction, Sweat, and Pressure
Not all pimples come from the inside out. Acne mechanica is triggered by physical factors: heat, friction, pressure, and occlusion against the skin. It’s common in athletes who wear helmets, shoulder pads, or tight gear. Football players, for instance, frequently develop breakouts along the chin from helmet straps. The combination of sweating, rubbing, and trapping heat against the skin irritates follicles and accelerates clogging.
You don’t have to be an athlete to experience this. Tight mask straps, backpack straps pressing on shoulders, resting your chin on your hand, or wearing a headband during workouts can all create the same effect. Wearing a clean, absorbent cotton layer between your skin and any equipment or tight clothing helps reduce the four contributors: occlusion, heat, friction, and pressure.
From Blackhead to Cyst
That initial microcomedone can evolve in several directions depending on how your body responds. If the plug stays near the surface and the pore remains open, the oil oxidizes when exposed to air, turning dark. That’s a blackhead. If the pore stays closed, the trapped oil and cells form a small white bump just under the surface: a whitehead. Neither of these involves significant inflammation, which is why they’re classified as non-inflammatory acne.
When bacteria multiply and your immune system gets involved, things escalate. A papule is a small, solid, inflamed bump without a visible pus-filled center, typically under one centimeter. When white blood cells accumulate and form visible pus at the tip, it becomes a pustule, what most people picture when they think of a pimple. If the follicle wall breaks deep beneath the skin and inflammation spreads into surrounding tissue, the result is a nodule: larger, deeper, more painful, and far more likely to scar. Cysts form when the body walls off the infection in a fluid-filled sac deep under the skin.
Skincare Products and Pore Clogging
Some ingredients in moisturizers, sunscreens, and makeup can contribute to clogged pores. The comedogenic scale rates ingredients from 0 (won’t clog pores) to 5 (highly likely to clog pores). However, this scale has real limitations. The original ratings came from applying ingredients at concentrations up to 100% on rabbit ears for two weeks. In actual products, concentrations are far lower. Isopropyl isostearate, for example, scores high at full strength but becomes mostly harmless at 5% concentration.
A more practical approach than memorizing comedogenic ratings: if you notice breakouts concentrated in areas where you apply a specific product, try removing it for a few weeks. Oil cleansers sometimes contain ingredients like isopropyl palmitate that are technically comedogenic but wash off quickly enough that they rarely cause problems. What sits on your skin for hours matters more than what rinses off in seconds.
How Common Acne Really Is
If you’re dealing with pimples, you’re far from alone. The overall global prevalence of acne sits around 20.5%, but that number rises sharply in younger age groups. Among 16 to 24 year olds, prevalence reaches 28.3%, and a European study of people aged 15 to 24 found rates as high as 57.8%. In the United States, a survey of adults in their twenties found that 51% of women and 43% of men reported active acne.
Acne also doesn’t always stop after adolescence. Roughly one in five people between ages 25 and 39 are diagnosed with it. Rates vary across demographics too. Acne is more prevalent in African American and Hispanic women (37% and 32%) compared to Asian, Caucasian, and Continental Indian women (23%, 24%, and 30%). Adult acne, particularly along the jawline and chin, is increasingly recognized as a distinct pattern often tied to hormonal fluctuations rather than the T-zone oiliness typical of teenage breakouts.