Acne develops when oil glands in your skin produce too much sebum, dead skin cells trap that oil inside your pores, bacteria multiply in the clogged pore, and your immune system responds with inflammation. Those four processes work together, but what sets them off varies from person to person. Your genetics, hormones, diet, stress levels, and even the products you put on your face all play a role in determining whether you break out and how severely.
The Four Processes Behind Every Breakout
Every pimple, blackhead, or cyst traces back to the same chain of events happening inside a hair follicle. First, your sebaceous (oil) glands ramp up production. Second, skin cells lining the follicle shed too quickly and clump together instead of clearing out, forming a plug. Third, a bacterium called Cutibacterium acnes, which normally lives harmlessly on your skin, thrives in that oxygen-deprived, oil-rich environment. Fourth, your immune system detects the bacterial overgrowth and launches an inflammatory response, creating the redness, swelling, and pain you see on the surface.
Not all of these steps need to go wrong at the same intensity for acne to appear. A blackhead, for instance, is mostly about excess oil and a clogged pore with minimal inflammation. A deep, painful cyst involves all four processes firing hard. Understanding which factors are driving your particular breakouts helps explain why certain treatments work for some people and not others.
Hormones Are the Biggest Driver
Androgens, a group of hormones that includes testosterone, are the primary signal telling your oil glands to produce more sebum. Androgen receptors are especially concentrated in the sebaceous glands on your face and scalp, which is why those areas tend to break out most. Your skin also contains an enzyme called 5-alpha reductase that converts testosterone into a more potent form, and this enzyme is particularly abundant in facial oil glands.
This is why acne peaks during puberty, when androgen levels surge, and why it tends to flare around menstrual periods, during pregnancy, or with conditions like polycystic ovary syndrome. In adult women with persistent acne, slightly elevated levels of a precursor hormone called DHEA-S are commonly observed, even when other hormone tests look normal. Stress hormones also feed into this system: corticotropin-releasing hormone (CRH), the same signal your brain sends to kick off the stress response, directly stimulates oil production in skin cells.
Your Genes Set the Stage
Twin studies estimate that acne is up to 85% heritable. That doesn’t mean 85% of people get acne. It means that among the factors determining how severe your acne is, roughly 85% of the variation comes down to the genes you inherited rather than environmental factors. If both of your parents had significant acne, your odds of dealing with it are substantially higher. Genetics influence how large your oil glands are, how sensitive they are to hormones, how your immune system responds to clogged pores, and how quickly your skin cells turn over.
The Bacteria on Your Skin Matter
C. acnes lives on everyone’s skin, but not all strains behave the same way. Certain subtypes are strongly associated with inflammatory acne. These strains produce higher levels of porphyrins, compounds that promote inflammation, and they release enzymes that break down the follicle wall, letting bacteria and oil leak into surrounding tissue. Your immune system then floods the area with inflammatory signals, which is what turns a clogged pore into an angry red bump.
The key insight here is that acne isn’t an infection you “catch.” It’s an imbalance. When the bacterial community on your skin shifts toward more inflammatory strains, or when excess oil gives those strains more fuel, the immune response escalates. This is also why harsh antibacterial scrubbing can sometimes make things worse: disrupting the overall microbial balance on your skin can favor the problematic strains.
Stress Makes Breakouts Worse
Stress doesn’t just make you feel like your skin is worse. There’s a direct biological pathway connecting your brain to your oil glands. When you’re stressed, your skin cells produce their own version of the stress hormone cascade. CRH promotes oil production and triggers inflammatory signals in the surrounding skin cells. On top of that, a nerve signaling molecule called substance P increases around sebaceous glands in acne-prone skin. Substance P stimulates both the growth of oil glands and the release of inflammatory molecules like IL-1, IL-6, and TNF-alpha.
Facial skin from acne patients shows a marked increase in substance P nerve fibers around sebaceous glands and around active lesions. So the connection between a stressful week and a fresh breakout isn’t in your head. Your nervous system is literally sending more pro-inflammatory, oil-stimulating signals to your skin.
Diet Plays a Role, but Not the One You Think
The relationship between food and acne is more nuanced than the old “chocolate causes pimples” claim. One study specifically looking at dietary glycemic index, glycemic load, and insulin levels in younger acne patients found no significant differences between those with acne and controls. So the simple story of “sugar spikes insulin, insulin causes acne” doesn’t hold up as neatly as some sources suggest.
What does have stronger evidence is the connection between diet and gut health. People with acne tend to have lower gut microbiome diversity and reduced levels of beneficial bacteria like Lactobacillus and Bifidobacterium. High-fat diets can reduce beneficial gut bacteria and increase compounds called lipopolysaccharides, which damage the intestinal lining and trigger bodywide inflammation. Stress compounds this effect: psychological stress alters gut bacteria, increases intestinal permeability, and allows inflammatory molecules to enter the bloodstream, potentially reaching the skin. The link between your gut and your skin is real, though the science is still mapping out exactly how strong the effect is compared to hormones and genetics.
Products That Clog Your Pores
Some skincare and cosmetic ingredients are more likely to block your pores than others. Dermatologists use a comedogenic rating scale from 0 (won’t clog pores) to 5 (very likely to clog pores). Among the most common offenders rated 4 or higher:
- Coconut oil and coconut butter (rating 4), popular in natural skincare but a frequent acne trigger
- Cocoa butter (rating 4), common in moisturizers and body lotions
- Isopropyl myristate (rating 5), found in many lotions and foundations as a texture enhancer
- Sodium lauryl sulfate (rating 5), a foaming agent in cleansers, shampoos, and toothpaste
- Wheat germ oil (rating 5)
- Algae extract and red algae (rating 5), increasingly popular in “clean beauty” products
If you’ve switched to a new moisturizer, sunscreen, or foundation and noticed new breakouts along your jawline, cheeks, or forehead within a few weeks, the product’s ingredient list is worth checking. Comedogenic ingredients don’t cause acne in everyone, but if you’re already prone to breakouts, they can tip the balance.
Physical Friction and Pressure
Acne mechanica is a specific type of breakout triggered by repeated pressure, heat, and friction against the skin. It shows up in predictable patterns: along the chin from helmet straps, across the forehead from tight hats or headbands, on the back and shoulders from backpack straps or sports padding, and even on areas pressed against a chair or bed for extended periods. Football players frequently develop it on their chins from helmet straps. If your breakouts consistently appear where clothing, gear, or equipment presses against your skin, friction is likely a contributing factor rather than hormones or diet.
Why Adult Acne Is Different
Teenage acne typically centers on the T-zone (forehead, nose, chin) and is driven primarily by the puberty-related surge in androgens. Adult acne, particularly in women, tends to cluster along the jawline and lower face, often flaring with menstrual cycles. Most adult women with persistent acne don’t show obvious signs of hormone imbalance on standard blood tests. Instead, their skin appears to have heightened local sensitivity to normal hormone levels, with overactive enzymes in the skin converting mild hormones into more potent forms.
Stress plays a proportionally larger role in adult acne than in teenage acne, partly because adults face chronic psychological stress that keeps the brain-skin hormone cascade activated over longer periods. The combination of hormone sensitivity, stress, and years of cumulative product use makes adult acne a different puzzle than the breakouts you had at 15, even though the underlying biology is the same four-step process.