Why do we
get acne?

Chocolate, poor hygiene, bad luck? The myths around acne are countless — and most of them are wrong. Yet behind every pimple, there's a precise and identifiable mechanism. Understanding why your skin reacts is the first step toward treating it effectively.

How acne forms: the physiological mechanism

Before talking about causes, you need to understand what's actually happening in your skin. Acne is the result of four phenomena that follow one another inside the same hair follicle (the small canal that holds a hair and a sebaceous gland).

1. Hyperseborrhea: the sebaceous gland produces too much sebum, the oily film meant to protect the skin
2. Hyperkeratinization: dead cells clog the follicle's opening, forming a plug
3. Bacterial proliferation: the Cutibacterium acnes bacteria (formerly P. acnes) multiplies in this clogged, sebum-rich environment
4. Inflammation: the immune system reacts, creating redness, swelling and sometimes pain

Depending on which stage dominates, the pimple takes a different shape: blackhead (open comedone), whitehead (closed comedone), red papule, pustule, or deep nodule. But the initial cause stays almost always the same: a dysregulation of the sebaceous gland.

The 5 real causes (in order of importance)

1. Hormones — the #1 factor

Hormones are by far the leading cause of acne. More precisely, the androgens (testosterone and its derivatives) stimulate the sebaceous glands and trigger sebum overproduction. That's why acne explodes during puberty, returns before periods, or sometimes appears at 25-35 in some women.

The imbalance is not always linked to an excess of hormones, but often to an increased sensitivity of the skin's receptors. With the same androgen levels, two skins can react very differently.

2. Genetics

If your parents had acne, you are statistically more likely to have it too. Genetics determine the sensitivity of your sebaceous glands, the thickness of your skin, and your inflammation type. They don't directly create acne, but they dictate how your skin reacts to triggers.

3. Chronic stress

Stress releases cortisol, a hormone that indirectly stimulates sebaceous glands and amplifies inflammation. It's not a myth: stressful periods (exams, grief, work overload) very often coincide with acne flare-ups. A classic Stanford University study showed a direct correlation between stress level and lesion severity in students during exam periods.

4. Diet (with nuances)

Contrary to what was long believed, diet does play a real role — but not just any kind. Recent studies point to two food groups:

• High glycemic index foods (sugar, white bread, pastries, sodas) which trigger insulin spikes and indirectly stimulate sebum production
• Dairy products, especially skim milk, rich in bovine hormones (IGF-1) that activate androgenic pathways

Dark chocolate rich in cocoa, on the other hand, has never been significantly correlated with acne. The culprits are sugary, milk-rich chocolate bars.

5. Unsuitable cosmetics

Some products are described as comedogenic: they clog pores and encourage comedone formation. Heavy plant oils (coconut, cocoa butter), certain silicones, and rich foundations are the main suspects. Conversely, overly stripping products can damage the skin barrier and cause a rebound effect: the irritated skin produces even more sebum to protect itself.

The myths to forget

Before going further, here are the most stubborn beliefs — and why they are wrong or far too simplistic.

"Chocolate causes pimples"

False, as it stands. No serious study has established a link between cocoa and acne. The real culprits are the refined sugar and the dairy in most industrial chocolate products.

"You need to wash your skin thoroughly to prevent acne"

False. Acne is not a matter of dirt. Washing your face three or four times a day, or using stripping products, damages the skin barrier and triggers a rebound effect. Two gentle cleansings per day, morning and evening, are enough.

"The sun cures acne"

Misleading. The sun temporarily dries out pimples and masks redness: it feels like the skin is improving. But in the medium term, the thickening of the stratum corneum caused by UV light clogs the pores and triggers a post-vacation rebound effect, often more severe than the initial state.

"Acne will eventually go away on its own"

Not always. For many people, yes. But untreated acne often leaves marks (red, brown or scars) that can stay for years. The earlier you act, the lower the risk of long-term damage.

Acne-prone skin is neither dirty nor at fault. It's a skin reacting to a precise internal imbalance, which needs to be identified before it can be corrected.

Acne by age: what changes

Acne doesn't show up the same way at every age, because the hormonal triggers are different.

Teenage acne (12-20 years)

Affects up to 85% of teenagers. It is mainly linked to puberty: the sudden surge of androgens stimulates the sebaceous glands. Mostly located on the forehead, nose and chin (the famous T-zone), it usually subsides around 18-22.

Adult acne (25-40 years)

Affects roughly 40% of women and 20% of men. Often hormonal (cycles, contraception, stress), it concentrates on the lower face: chin, jawline, neck. It can appear in someone who never had teenage acne.

Late-onset acne (40+)

More rare, it sometimes appears during pre-menopause or hormonal shifts. It can also be triggered by certain medications (corticosteroids, lithium) or by an undiagnosed rosacea.

When should you see a dermatologist?

Mild acne can be treated very well at home with a suitable routine. But certain signs should push you to consult without delay:

• Nodular or cystic acne: large, deep, painful pimples that last several weeks
• Forming scars: depressed (ice pick, boxcar) or raised
• No improvement after 3 months of a well-followed routine
• Major psychological impact: social anxiety, lowered self-esteem, avoidance
• Sudden acne after 25 in someone who never had it before, especially if linked to cycle disorders

In these cases, medical treatments (topical retinoids, antibiotics, isotretinoin, hormonal therapy) can transform the trajectory of your skin.

What to do, concretely?

Understanding causes is useful, but action is what matters. Here are the three steps that change everything:

1. Identify your dominant cause. Hormonal? Stress? Cosmetics? Diet? Often, several factors add up — but one dominates, and that's the one to treat first.
2. Build a coherent routine. Gentle cleansing, targeted treatment (salicylic acid, niacinamide, retinol depending on the profile), non-comedogenic moisturizing and sun protection. No miracle product: what works is consistency.
3. Be patient. The full skin renewal cycle is 28 to 40 days. No treatment, even medical, gives results before 6 to 12 weeks. Three months minimum before evaluating a protocol.

In summary

Acne is neither inevitable nor a hygiene issue. It's an identifiable imbalance, almost always triggered by hormones, modulated by genetics, and amplified by stress, diet and certain cosmetics.

The myths — chocolate, poor hygiene, beneficial sun — make you waste time. Pinpointing exactly what triggers your acne is the only real shortcut to skin that calms down. And it's also the promise of a routine that doesn't make you spin in circles.