Definition and epidemiology
Acne vulgaris is a chronic inflammatory disease of the pilosebaceous unit resulting from follicular hyperkeratinization, excess sebum production, bacterial colonization, and inflammation. The condition manifests as a spectrum of lesions including comedones (open and closed), inflammatory papules, pustules, nodules, and cysts, primarily affecting areas with high sebaceous gland density.
Epidemiology: Acne affects approximately 85% of individuals between ages 12-24 years, making it one of the most common dermatologic conditions worldwide. Peak incidence occurs during mid-to-late adolescence (ages 14-17 in females, 16-19 in males). While traditionally considered a disease of adolescence, adult acne affects up to 50% of women and 25% of men in their twenties, and approximately 15% of women continue to experience acne into their forties. No significant racial or ethnic predilection exists, though severity and scarring patterns may vary. Males typically experience more severe disease, while post-adolescent acne is more common in females, often with a hormonal component.
- Acne pathogenesis: follicular hyperkeratinization, excess sebum, C. acnes colonization, inflammation.
- Topical retinoids are first-line for most acne; normalize keratinization and are comedolytic; contraindicated in pregnancy.
- Always combine topical antibiotics with benzoyl peroxide to prevent antibiotic resistance.
- Oral isotretinoin is highly effective for severe/scarring acne but is teratogenic; requires iPLEDGE program.
- Tetracyclines (doxycycline, minocycline) are first-line oral antibiotics; avoid in children < 8 years and pregnancy.
- Key differentiator from rosacea: acne has comedones; rosacea does not.
- Hormonal therapy (OCPs, spironolactone) effective in females with hormonal acne patterns.
- Post-inflammatory hyperpigmentation is common in darker skin types; azelaic acid can help.
Etiology and risk factors
Acne is a multifactorial disease without a single causative agent. The primary factors include:
Hormonal influences
Androgens (testosterone, dihydrotestosterone, DHEA-S) stimulate sebaceous gland activity and sebum production, explaining the onset at puberty and association with conditions like polycystic ovary syndrome (PCOS). Hormonal fluctuations during menstruation can trigger flares in women.
Genetic factors
First-degree relatives of affected individuals have a significantly increased risk. Twin studies suggest heritability of approximately 80%. Genetic factors influence sebum production, follicular keratinization, and inflammatory response.
Risk factors
- Endocrine disorders: PCOS, congenital adrenal hyperplasia, androgen-secreting tumors
- Medications: corticosteroids, androgens, lithium, phenytoin, isoniazid, high-dose B vitamins
- Mechanical factors: occlusive clothing, sports equipment (acne mechanica), repetitive rubbing or pressure
- Cosmetics: comedogenic products, heavy oils and pomades (particularly in acne cosmetica and pomade acne)
- High glycemic index diet: emerging evidence suggests refined carbohydrates and dairy may exacerbate acne in susceptible individuals
- Stress: correlates with flares, possibly through neuropeptide and cortisol effects on sebaceous glands
- Occupational exposures: industrial oils, coal tar derivatives, chlorinated hydrocarbons
Important: Diet has a controversial role; while chocolate and fatty foods have not been definitively proven causative, some studies suggest high glycemic load and dairy products may worsen acne in certain individuals.
Pathophysiology
Acne pathogenesis involves four key interconnected processes:
1. Follicular hyperkeratinization
Abnormal desquamation of follicular epithelium and increased keratinocyte proliferation lead to microcomedone formation. Keratinocytes fail to separate normally and accumulate within the follicle, creating a plug that obstructs sebum outflow. This process is androgen-mediated and represents the initial lesion in acne formation.
2. Excess sebum production
Androgens stimulate sebaceous glands to increase in size and sebum production. Sebum provides a lipid-rich, anaerobic environment ideal for bacterial colonization. Individuals with acne produce more sebum with altered lipid composition compared to unaffected individuals.
3. Cutibacterium acnes colonization
C. acnes (formerly Propionibacterium acnes), a gram-positive anaerobic bacterium that is part of normal skin flora, proliferates within the sebum-filled, obstructed follicle. The bacteria produce lipases that hydrolyze sebum triglycerides into free fatty acids, which are pro-inflammatory. C. acnes also activates toll-like receptor 2 (TLR-2) and produces chemotactic factors.
4. Inflammation and immune response
Follicular wall rupture releases keratin, sebum, and bacteria into the dermis, triggering a robust inflammatory response. Neutrophils and lymphocytes infiltrate, releasing inflammatory mediators (IL-1, IL-8, TNF-α). This process creates the clinical inflammatory lesions: papules, pustules, and nodules. Innate immune activation occurs even before follicular rupture in many cases.
Scarring results from severe inflammation and dermal matrix destruction, with collagen deposition during healing creating atrophic (ice-pick, rolling, boxcar) or hypertrophic scars.
Clinical features
Acne presents with a polymorphic eruption typically involving the face (99%), back (60%), and chest (15%). The distribution correlates with sebaceous gland density.
Non-inflammatory lesions
- Closed comedones (whiteheads): 1-2 mm flesh-colored or white papules with no visible central opening, representing obstructed follicular orifices
- Open comedones (blackheads): dilated follicular openings filled with oxidized keratin and sebum, appearing as dark plugs (the color is due to melanin and oxidation, not dirt)
Inflammatory lesions
- Papules: small (< 5 mm) erythematous, tender, raised lesions without visible purulent material
- Pustules: lesions with visible central purulent material, yellowish-white center
- Nodules: large (≥ 5 mm), painful, deep-seated, firm lesions extending into deeper dermis and subcutaneous tissue
- Cysts: fluctuant, pus-filled nodules (true epithelial-lined cysts are rare; the term is often misused)
Severity classification
Multiple systems exist; a practical approach:
- Mild: predominantly comedonal with few inflammatory lesions
- Moderate: greater number of inflammatory papules and pustules, with comedones
- Severe: extensive inflammatory lesions, nodules, possible scarring (includes acne conglobata and acne fulminans)
Variants
- Acne fulminans: rare, severe variant with sudden onset of ulcerating nodular acne, systemic symptoms (fever, arthralgia), and laboratory abnormalities; more common in males
- Acne conglobata: severe chronic form with interconnecting abscesses, draining sinuses, and significant scarring
- Neonatal acne: occurs in first few weeks of life, typically self-limited
- Infantile acne: onset 3-6 months, may require treatment, can indicate hyperandrogenism
Post-inflammatory changes include erythema (transient vascular response) and hyperpigmentation (more pronounced in darker skin types), both of which resolve over months without scarring.
Diagnosis
Acne is a clinical diagnosis based on history and physical examination. No laboratory tests or imaging are routinely required.
History
- Age of onset, duration, previous treatments and responses
- Current skincare and cosmetic products
- Medications (especially acne-inducing drugs)
- Menstrual history in females, signs of hyperandrogenism
- Family history of acne
- Psychosocial impact and quality of life assessment
Physical examination
Systematic skin examination documenting:
- Distribution and extent of involvement
- Types of lesions present (comedonal, inflammatory, or mixed)
- Severity assessment
- Presence of scarring (type and extent)
- Post-inflammatory changes
In females with treatment-resistant acne, hirsutism, irregular menses, or rapid onset, examine for signs of hyperandrogenism: hirsutism, male-pattern alopecia, virilization.
Laboratory evaluation
Not routinely indicated but consider in specific scenarios:
- Hormonal workup (total and free testosterone, DHEA-S, LH/FSH ratio, 17-hydroxyprogesterone): indicated in females with signs of hyperandrogenism, sudden onset severe acne in adulthood, treatment resistance, or menstrual irregularities suggestive of PCOS or other endocrine disorders
- Pregnancy test: before initiating isotretinoin or hormonal therapies in females of reproductive age
- Lipid panel and liver function tests: baseline before isotretinoin therapy
Microbiological studies
Cultures are not routinely performed. Bacterial culture may be considered in treatment-resistant cases to assess for antibiotic-resistant strains, though C. acnes antibiotic susceptibility testing is not standardized.
Skin biopsy
Rarely necessary; may be performed if diagnosis is uncertain or to rule out mimickers such as rosacea, folliculitis, or gram-negative folliculitis.
Differential diagnosis
Several conditions can mimic acne vulgaris:
- Rosacea: facial erythema, flushing, telangiectasias, inflammatory papules and pustules but no comedones; typically affects older adults (age > 30), central facial distribution
- Folliculitis: bacterial (Staphylococcus aureus) or fungal (Malassezia); follicular pustules without comedones; may be pruritic; distribution can involve areas with less sebaceous activity; fungal folliculitis responds to antifungals, not typical acne treatments
- Perioral dermatitis: papules and pustules around mouth, nasolabial folds, periorbital area; often associated with topical corticosteroid use; spares vermillion border
- Pseudofolliculitis barbae: inflammatory papules and pustules in beard area due to ingrown hairs; more common in individuals with curly hair
- Hidradenitis suppurativa: chronic inflammatory condition affecting intertriginous areas (axillae, groin, inframammary); nodules, abscesses, sinus tracts, scarring; involves apocrine glands
- Chloracne: occupational acne due to halogenated aromatic hydrocarbons; comedones and cysts, often in unusual distribution (behind ears, shoulders)
- Drug-induced acne: sudden onset, monomorphic lesions (often all pustular), temporal relationship with medication initiation
- Gram-negative folliculitis: complication of long-term antibiotic therapy; sudden flare of pustules, often perinasal
- Acneiform eruptions: systemic conditions (Cushing syndrome), mechanical occlusion, or contact with comedogenic substances
Key differentiating feature: true acne vulgaris includes comedones, which are absent or rare in most mimickers.
Management
Treatment is tailored to severity, lesion types, patient factors, and previous treatment responses. The goals are to reduce lesions, prevent scarring, and minimize psychosocial impact.
General measures
- Gentle cleansing with mild, non-comedogenic products twice daily
- Avoid mechanical trauma, picking, and squeezing lesions
- Use non-comedogenic cosmetics and sunscreens
- Patient education about disease chronicity and realistic treatment expectations (improvement typically takes 6-8 weeks)
Topical therapy
Retinoids (tretinoin, adapalene, tazarotene): normalize follicular keratinization, are comedolytic, and have anti-inflammatory properties. First-line for most acne types, particularly comedonal. Common side effects include dryness, erythema, and increased sun sensitivity; tretinoin is also degraded by UV light, so retinoids are typically applied at night. Topical retinoids are contraindicated in pregnancy due to teratogenicity. Adapalene has better tolerability.
Benzoyl peroxide: antimicrobial (bactericidal against C. acnes), anti-inflammatory, does not induce bacterial resistance. Available in various concentrations. Can bleach fabrics. Often combined with topical antibiotics to reduce resistance.
Topical antibiotics (clindamycin, erythromycin): anti-inflammatory and antibacterial. Should always be combined with benzoyl peroxide to minimize antibiotic resistance. Not recommended as monotherapy.
Azelaic acid: antimicrobial, anti-inflammatory, and reduces post-inflammatory hyperpigmentation. Useful in patients who cannot tolerate retinoids or in those with darker skin types at risk for hyperpigmentation.
Salicylic acid: comedolytic, keratolytic; generally less effective than retinoids but useful in mild comedonal acne.
Mild acne (comedonal, few inflammatory lesions)
- Topical retinoid alone or with benzoyl peroxide
- Alternative: azelaic acid or salicylic acid
Moderate acne (inflammatory papules/pustules, more extensive)
- Topical retinoid plus benzoyl peroxide plus topical antibiotic, OR
- Topical retinoid plus benzoyl peroxide plus oral antibiotic
- Consider oral contraceptives in females (see below)
Severe acne (nodular, scarring, or treatment-resistant)
- Oral isotretinoin: highly effective for severe, recalcitrant, or scarring acne. Induces long-term remission in many patients. Requires careful monitoring due to teratogenicity and other side effects (dry skin/lips, elevated triglycerides and liver enzymes, myalgias, rare psychiatric effects). Mandatory pregnancy prevention program (iPLEDGE in US) for females of reproductive potential.
- Alternative: combination of oral antibiotics, topical retinoids, and benzoyl peroxide, with consideration of hormonal therapy in females
Oral antibiotics
Tetracyclines (doxycycline, minocycline) are first-line oral antibiotics due to anti-inflammatory properties and activity against C. acnes. Avoid in children < 8 years and pregnancy. Alternatives include trimethoprim-sulfamethoxazole or macrolides (though resistance is increasing). Duration should be limited (typically 3-4 months) to minimize resistance; always combine with benzoyl peroxide topically.
Hormonal therapy (females)
Combined oral contraceptives: containing ethinyl estradiol with anti-androgenic progestins (drospirenone, norgestimate, norethindrone) are effective for moderate acne in females. Reduce sebum production by suppressing ovarian androgen production.
Spironolactone: androgen receptor antagonist; effective for hormonal acne in adult females, particularly with premenstrual flares, lower face/jawline distribution. Requires monitoring for hyperkalemia; contraindicated in pregnancy.
Procedural treatments
- Intralesional corticosteroids: triamcinolone for large, painful nodules; provides rapid symptom relief
- Comedone extraction: manual removal of open and closed comedones
- Chemical peels: adjunctive therapy for comedonal acne and post-inflammatory hyperpigmentation
- Laser and light therapies: variable evidence; may be adjunctive for inflammatory acne and scarring
Acne scar treatment
Addressed after active acne is controlled. Options include chemical peels, microneedling, laser resurfacing, subcision, dermal fillers, and punch excision/elevation depending on scar type.
Important: Antibiotic stewardship is critical. Avoid prolonged antibiotic monotherapy; always combine with benzoyl peroxide. International guidelines (AAD, European guidelines) emphasize topical retinoids as foundational therapy.
Complications and prognosis
Complications
Scarring: the most significant physical complication, occurring in up to 95% of individuals with acne to some degree. Types include:
- Atrophic scars: ice-pick (narrow, deep), rolling (broader, undulating), boxcar (wider, sharp edges)
- Hypertrophic scars and keloids: more common on trunk, particularly in individuals with darker skin types
Scarring risk is increased with severe acne, delayed treatment, nodular/cystic lesions, and manipulation of lesions.
Post-inflammatory hyperpigmentation: particularly problematic in darker skin types (Fitzpatrick types IV-VI); can persist for months to years but typically resolves without intervention.
Psychological impact: acne significantly affects quality of life, self-esteem, and social functioning. Increased rates of anxiety, depression, and social withdrawal are documented. Severe cases correlate with higher psychological morbidity.
Gram-negative folliculitis: superinfection that can occur with prolonged antibiotic use, presenting as sudden flare of pustular lesions.
Acne fulminans: rare systemic complication with ulcerative lesions, fever, arthralgias, and potential for bone lesions.
Prognosis
Most adolescent acne improves by the mid-twenties, though approximately 10-15% of individuals continue to experience acne into adulthood. Adult-onset acne, particularly in females, may persist longer and have a more chronic course.
With treatment: most patients achieve significant improvement with appropriate therapy. Topical retinoids and benzoyl peroxide improve mild-to-moderate acne in 60-70% of patients. Oral isotretinoin achieves long-term remission in approximately 70-80% of patients after a full course, though relapse can occur.
Without treatment: acne tends to fluctuate, with periods of exacerbation and partial remission. Untreated severe acne invariably leads to scarring.
Early intervention significantly reduces the risk of permanent scarring and psychological sequelae. The emphasis is on starting effective treatment promptly rather than waiting for spontaneous resolution.
Acne pathogenesis remembered as "FISH": Follicular hyperkeratinization, Increased sebum, Staph/C. acnes (bacterial colonization), Host inflammatory response.
Practice questions
1. A 16-year-old male presents with a 1-year history of facial lesions. Examination reveals open and closed comedones on the forehead and cheeks, with scattered erythematous papules and pustules. There are no nodules or scarring. His older brother had similar acne that resolved with treatment. What is the most appropriate initial therapy?
2. A 28-year-old woman with acne vulgaris has been treated with multiple topical agents and oral doxycycline for 4 months with minimal improvement. She has moderate inflammatory acne and early scarring on her cheeks and jawline. Her acne worsens premenstrually. She has regular menstrual cycles and no hirsutism. What is the next best step in management?
3. A 19-year-old male with severe nodular acne and significant scarring is started on oral isotretinoin. Before initiating therapy, which of the following laboratory tests must be obtained?
Frequently asked questions
What causes acne?
Acne is caused by four interconnected factors: abnormal follicular keratinization creating plugged pores, excess sebum production stimulated by androgens, proliferation of Cutibacterium acnes bacteria within obstructed follicles, and subsequent inflammation. Hormonal changes during puberty, genetic predisposition, and certain medications contribute to these processes. While diet's role is debated, high glycemic foods and dairy may worsen acne in some individuals. Stress and mechanical factors can also trigger flares.
What are the first symptoms of acne?
The earliest signs of acne are comedones—small bumps called blackheads (open comedones with dark centers) or whiteheads (closed comedones appearing as flesh-colored bumps). These typically appear on the face, especially the forehead and nose, during early adolescence. As acne progresses, inflammatory lesions develop: red, tender papules and pustules (pimples with white centers). Nodules and cysts represent more severe forms and appear as larger, painful lumps beneath the skin surface.
How is acne diagnosed?
Acne is diagnosed clinically based on physical examination showing characteristic comedones, papules, pustules, or nodules in typical locations (face, chest, back). No laboratory tests are routinely needed. The doctor assesses severity, lesion types, and presence of scarring. Hormonal testing may be ordered in females with signs of hyperandrogenism (excessive hair growth, irregular periods, treatment resistance) to rule out conditions like polycystic ovary syndrome. Blood tests are required before starting isotretinoin.
Is acne curable?
Acne is manageable and controllable but not permanently curable in all cases. Most adolescent acne resolves by the mid-twenties without intervention, though scarring may remain. Treatment with topical retinoids, benzoyl peroxide, and antibiotics effectively controls symptoms in most patients. Oral isotretinoin can induce long-term remission in 70-80% of severe cases after one course. However, acne can recur, particularly adult-onset acne in females, which tends to be more chronic and may require ongoing maintenance therapy.
Acne vs rosacea — what is the difference?
The key difference is that acne has comedones (blackheads and whiteheads) while rosacea does not. Acne typically begins in adolescence and affects younger individuals, whereas rosacea usually starts after age 30. Rosacea presents with persistent facial redness, flushing, visible blood vessels, and inflammatory papules/pustules on the central face. Acne affects face, chest, and back with mixed inflammatory and non-inflammatory lesions. Rosacea may have ocular symptoms and worsens with triggers like alcohol and spicy foods.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: L70
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.