Acne: What Could Be Causing It?

How Acne Forms at the Follicular Level

Acne is a disease of the pilosebaceous unit. Each breakout starts when keratinocytes lining the hair follicle shed too quickly and clump together, forming a microcomedo that traps sebum beneath the skin surface [1]. Sebaceous glands, stimulated primarily by circulating androgens, produce excess oil that feeds the process.

Once a follicle is plugged, the anaerobic environment favors colonization by Cutibacterium acnes (formerly Propionibacterium acnes). This bacterium triggers innate immune responses through toll-like receptor 2 (TLR2) activation on surrounding keratinocytes and macrophages [2]. The resulting inflammatory cascade produces the papules, pustules, and deeper nodules that define clinical acne.

A 2012 meta-analysis published in the British Journal of Dermatology estimated global acne prevalence at 9.4%, making it one of the most common skin conditions seen in primary care [3]. The severity spectrum is wide. Some patients develop only scattered comedones (blackheads and whiteheads), while others progress to painful nodulocystic disease that carries a high risk of permanent scarring.

The four established pillars of acne pathogenesis are follicular hyperkeratinization, androgen-driven sebum overproduction, C. acnes proliferation, and inflammation [1]. Newer research adds a fifth consideration: disruption of the skin microbiome balance, where reduced microbial diversity may permit pathogenic C. acnes phylotypes to dominate [2].

Hormonal Causes: Androgens, Cycles, and Endocrine Disorders

Androgens are the single most important hormonal driver of acne. Testosterone and its more potent metabolite dihydrotestosterone (DHT) bind receptors on sebocytes, directly increasing sebum production [4]. This explains why acne peaks during puberty, when adrenal and gonadal androgen output surges.

Adult women face a second wave. Premenstrual flares affect an estimated 63% of acne-prone women in the days before menstruation, driven by the relative drop in estrogen that unmasks androgen activity [5]. The pattern is predictable: lesions concentrate along the jawline and chin, areas with high sebaceous gland density.

Polycystic ovary syndrome remains the most common endocrine disorder linked to persistent adult female acne. A 2023 systematic review in Fertility and Sterility found that acne was present in 20 to 30% of women meeting Rotterdam criteria for PCOS, often alongside hirsutism and irregular menses [6]. Other androgen-excess conditions to consider include congenital adrenal hyperplasia (nonclassic 21-hydroxylase deficiency), androgen-secreting tumors, and Cushing syndrome.

The 2023 American Academy of Dermatology (AAD) guideline on acne management states: "Hormonal evaluation should be considered in female patients with treatment-resistant acne, especially when accompanied by signs of hyperandrogenism such as hirsutism, androgenic alopecia, or menstrual irregularity" [7].

Thyroid dysfunction, while not a direct acne trigger, can worsen skin quality and alter sebum composition. Hypothyroidism slows epidermal turnover, contributing to follicular plugging in some patients.

Genetic Predisposition and Family History

Your genes set the baseline. Twin studies show acne concordance rates of roughly 81% in monozygotic twins versus 50% in dizygotic twins, confirming a strong hereditary component [8]. If both parents had acne, the odds of their children developing it increase three to four-fold compared to peers with unaffected parents.

Specific genetic variants influence multiple steps in the pathogenesis pathway. Polymorphisms in the TNF-alpha promoter region, IL-1A, and CYP1A1 genes have all been associated with acne susceptibility in genome-wide studies [9]. These variants affect inflammatory signaling, androgen metabolism, and sebocyte behavior.

Genetic predisposition also determines how your sebaceous glands respond to a given level of androgen. Two people with identical testosterone levels may have dramatically different acne severity based on the density and sensitivity of androgen receptors in their skin [4]. This explains why some patients break out despite normal lab values.

Genetics cannot be modified, but understanding your family history helps set realistic treatment expectations and guides the aggressiveness of early intervention.

Medications and Substances That Trigger Acne

Drug-induced acne (sometimes called acneiform eruption) has a distinct clinical pattern: monomorphic papulopustules that appear suddenly, often on the trunk, with few or no comedones. Recognizing this pattern prevents unnecessary escalation of acne-specific therapy when the real fix is adjusting the offending medication.

The most common culprits include:

• Corticosteroids (oral and topical): steroid acne typically appears within 2 weeks of initiation, presenting as uniform inflammatory papules on the chest, shoulders, and upper back [10]
• Lithium: worsens acne in up to 45% of patients on long-term therapy [10]
• Anabolic-androgenic steroids: directly increase sebum production through androgen receptor activation
• Certain anticonvulsants: phenytoin and phenobarbital have well-documented associations
• Isoniazid and rifampin: tuberculosis therapy can trigger acneiform reactions
• EGFR inhibitors: cetuximab and erlotinib cause an acne-like rash in 50 to 80% of patients, though this is mechanistically distinct from true acne vulgaris [11]
• Progestins: some progestin-only contraceptives, particularly those with higher androgenic activity (levonorgestrel), can worsen acne

Dr. Julie Harper, a board-certified dermatologist and past president of the American Acne and Rosacea Society, has noted: "One of the most overlooked steps in an acne evaluation is a thorough medication history. Patients often don't connect their new prescription with a breakout that started two weeks later" [12].

Testosterone replacement therapy (TRT) predictably increases acne risk. Men starting TRT should be counseled that acne is among the most common side effects, affecting roughly 15 to 25% of patients in clinical cohorts, and usually responds to standard topical therapy [13].

Dietary and Lifestyle Factors

The link between diet and acne has been debated for decades. Recent epidemiological evidence, while not establishing causation, identifies two dietary patterns with the strongest associations.

High-glycemic-load diets raise insulin and insulin-like growth factor 1 (IGF-1), both of which stimulate androgen production and sebocyte proliferation. A randomized controlled trial of 43 young men published in the American Journal of Clinical Nutrition found that a low-glycemic-load diet reduced acne lesion counts by 23.5% over 12 weeks versus controls [14]. The mechanism is biologically plausible: insulin activates the mTORC1 pathway, a nutrient-sensing system that drives sebaceous lipogenesis.

Dairy, particularly skim milk, shows a modest positive association with acne in large cohort studies. The Nurses' Health Study II (N=47,355) found a positive association between skim milk intake and physician-diagnosed acne during adolescence [15]. Whey protein supplements appear to carry a similar signal, likely through their insulin-stimulating properties.

Stress operates through the hypothalamic-pituitary-adrenal (HPA) axis. Corticotropin-releasing hormone (CRH) receptors exist on sebocytes, and emotional stress increases both cortisol and adrenal androgens [16]. A study of 215 university students found acne severity correlated significantly with self-reported stress levels during examination periods [16].

Smoking data is mixed. Some studies find a positive association with comedonal (non-inflammatory) acne, while others show no relationship. The evidence is not strong enough to list smoking as a primary driver.

Sleep deprivation and its downstream effects on cortisol and inflammatory cytokines may contribute, though direct trials remain sparse.

Acne in Adults Over 25: Why Breakouts Persist

Adult acne is not residual teenage acne. It is a distinct clinical entity. Roughly 43% of adults in their 30s and 12% in their 50s report active acne, according to a cross-sectional study published in the Journal of the American Academy of Dermatology [17].

Women are disproportionately affected. Adult female acne typically presents with deep, tender nodules along the lower face and neck, flares premenstrually, and responds poorly to standard antibiotic therapy [17]. The underlying cause is usually hormonal. Evaluation should include total and free testosterone, DHEA-S, and consideration of PCOS screening if other signs of androgen excess are present.

In men over 25, persistent acne may signal ongoing androgenic stimulation from exogenous sources (testosterone therapy, supplements, performance-enhancing drugs) or may simply reflect genetic sebaceous gland sensitivity. Late-onset acne in either sex, especially if sudden, warrants evaluation for androgen-secreting tumors and medication review.

Adult acne also has a significant psychological burden. A 2018 study in the British Journal of Dermatology found that adults with acne had a 63% increased risk of developing major depressive disorder compared to age-matched controls, underscoring the importance of treating the condition rather than dismissing it as cosmetic [18].

Differential Diagnosis: Conditions That Mimic Acne

Not every papule on the face is acne vulgaris. Misdiagnosis leads to treatment failure and delays appropriate care.

Rosacea (papulopustular subtype) presents with central facial erythema, telangiectasias, and inflammatory papules without comedones. The absence of comedones is the key distinguishing feature. Rosacea tends to appear after age 30 and is worsened by triggers like alcohol, spicy food, and heat.

Perioral dermatitis produces grouped papules and fine scaling around the mouth, nasolabial folds, and sometimes the eyes. It is often triggered or worsened by topical corticosteroids. Treatment involves stopping the offending steroid and initiating topical metronidazole or oral tetracyclines.

Folliculitis (bacterial, fungal, or gram-negative) produces monomorphic pustules centered on hair follicles. Pityrosporum folliculitis, caused by Malassezia yeast, is commonly mistaken for acne on the chest and back. It does not respond to standard acne therapy but clears with antifungal agents like oral fluconazole or topical ketoconazole.

Hidradenitis suppurativa (HS) involves recurrent painful nodules and abscesses in intertriginous areas (axillae, groin, under breasts). HS and acne can coexist, but HS requires different management strategies.

Milia are small epidermal cysts that appear as firm white bumps, most commonly around the eyes. They are benign and do not represent acne, though patients frequently confuse the two.

Evidence-Based Treatment by Severity

The 2024 AAD guidelines organize acne treatment into a stepped approach based on severity [7].

Mild acne (comedones with few papules): topical retinoids (adapalene 0.1% or tretinoin 0.025 to 0.05%) combined with benzoyl peroxide 2.5 to 5%. Adapalene 0.1% is available over the counter as Differin. A 12-week randomized trial (N=653) showed adapalene 0.1% gel reduced total lesion counts by 63% compared to vehicle [19].

Moderate acne (widespread papules and pustules): add a topical antibiotic (clindamycin 1%) always paired with benzoyl peroxide to reduce resistance development. Fixed-dose combinations (adapalene/benzoyl peroxide, clindamycin/benzoyl peroxide) improve adherence.

Moderate-to-severe acne or treatment failure after 3 months: oral antibiotics. Doxycycline 50 to 100 mg daily for 3 months is first-line. Sarecycline, a narrow-spectrum tetracycline FDA-approved for acne in 2018, showed a 46.6% reduction in inflammatory lesions at 12 weeks in the phase 3 SC1401 trial (N=483) [20].

Severe nodulocystic acne or scarring: oral isotretinoin (0.5 to 1.0 mg/kg/day for 15 to 20 weeks). Isotretinoin is the only therapy that addresses all four pathogenic factors simultaneously. Cumulative doses of 120 to 150 mg/kg yield long-term remission rates of roughly 60 to 80% [21]. iPLEDGE registration and monthly pregnancy testing are mandatory for all patients of reproductive potential.

Hormonal therapy (females only): combined oral contraceptives containing ethinyl estradiol with a low-androgenic progestin (norgestimate, drospirenone) or spironolactone 50 to 200 mg daily. The Endocrine Society recommends hormonal therapy as adjunctive treatment for women with acne and documented hyperandrogenism [22].

When to See a Clinician

Most mild acne responds to over-the-counter adapalene and benzoyl peroxide within 8 to 12 weeks. Seek clinical evaluation when:

• Nodular or cystic lesions are present (these carry high scarring risk)
• Over-the-counter therapy fails after 12 weeks of consistent use
• Acne is accompanied by signs of hyperandrogenism (irregular periods, excess facial hair, scalp thinning)
• Onset is sudden in adulthood without an obvious medication trigger
• Acne is causing significant psychological distress or social withdrawal
• Post-inflammatory hyperpigmentation or scarring is developing

Early intervention with prescription therapy, particularly retinoids, prevents the scarring that is far more difficult to treat after the fact. A referral to dermatology is appropriate for any patient being considered for isotretinoin or for diagnostic uncertainty between acne and its mimics.

The AAD recommends that patients with moderate-to-severe acne receive prescription therapy within 3 months of onset to minimize permanent scarring [7]. Starting adapalene 0.1% gel nightly with benzoyl peroxide 5% wash each morning remains the most cost-effective first step for patients without access to immediate specialist care.