Acne Vulgaris

• Androgenic Stimulation and Sebum Production: The initiation of acne correlates temporally with increases in circulating androgens during puberty, particularly free testosterone and dihydrotestosterone (DHT). Androgens bind to androgen receptors in sebaceous glands, upregulating lipogenic enzymes including fatty acid synthase and acetyl-CoA carboxylase, resulting in quantitative and qualitative changes in sebaceous lipid composition. Increased sebum production (seborrhea) is essential for acne development—patients with negligible sebum production do not develop comedonal acne. The sebum becomes enriched in triglycerides, squalene, and cholesterol esters while depleting linoleic acid, creating a lipid milieu that promotes follicular colonization by Cutibacterium acnes. Notably, sebaceous gland sensitivity to circulating androgens varies genetically, explaining why some individuals with normal androgen levels develop severe acne while others with elevated androgens remain clear.

• Follicular Hyperkeratinization and Comedone Formation: The follicular epithelium undergoes aberrant keratinization (not increased cell production alone, but abnormal differentiation and cohesion) resulting in retention of keratin and sebaceous material. In normal follicles, keratinocytes are shed individually; in acne-prone follicles, keratinocytes exhibit increased adhesion through upregulation of desmosomal proteins and reduced production of ceramides, creating cohesive keratin plugs. This process is driven by elevated expression of Toll-like receptors (particularly TLR-2 and TLR-4) and dysregulation of innate immune mediators including substance P and corticotropin-releasing hormone (CRH), which increase within the follicle during stress—explaining the clinical observation that acne flares during psychological stress. The retained keratin and sebum form the comedone: blackheads (open comedones) appear dark due to oxidation of melanin and sebaceous material, not dirt, while whiteheads (closed comedones) remain covered by follicular epithelium. Progressive impaction creates a microenvironment with elevated pH and reduced oxygen tension, promoting anaerobic bacterial growth.

• ***Cutibacterium acnes* Colonization and Inflammatory Response**: Cutibacterium acnes (the gram-positive anaerobic rod formerly classified as Propionibacterium acnes) colonizes the follicular microenvironment in all individuals, but acne-prone patients harbor lipophilic strains with enhanced virulence factors. The bacterium produces multiple immunogenic compounds: lipopolysaccharide (LPS) and peptidoglycans activate pattern recognition receptors (Toll-like receptors 2 and 4) on keratinocytes and macrophages, triggering innate immune responses. Cutibacterium acnes secretes hyaluronidase and lipases that damage the follicular epithelium and generate pro-inflammatory free fatty acids from triglyceride hydrolysis. Bacterial strains are classified as acne-associated (highly pro-inflammatory) versus non-acne-associated (commensal), with the former possessing genomic islands encoding secreted factors. Activation of TLR-2 and TLR-4 upregulates expression of IL-12, TNF-α, IL-8, and IL-6, recruiting neutrophils and macrophages. The resulting innate immune response is disproportionate relative to bacterial load, suggesting dysregulation of immune tolerance. The follicular rupture releases bacterial antigens into the dermis, intensifying inflammation and explaining the transition from comedones to papules and pustules.

• Hormonal and Inflammatory Mediator Amplification Loop: Once initiated, acne is perpetuated by positive feedback loops involving neuropeptides and cytokines. Stress-induced release of CRH from nerve fibers and the hypothalamic-pituitary axis increases both sebaceous gland activity and follicular hyperkeratinization. Elevated intrafollicular levels of prostaglandin E2 (PGE2) and other eicosanoids amplify neutrophil recruitment and IL-8 production. IGF-1 (insulin-like growth factor 1) signaling, enhanced by high-glycemic-index diets and dairy consumption (which contains growth factors), upregulates androgen-responsive genes in sebaceous glands and increases follicular proliferation. The production of reactive oxygen species (ROS) by activated neutrophils and macrophages causes lipid peroxidation, further impairing the follicular barrier. This multi-hit inflammatory cascade explains why topical antibiotics alone are insufficient—they eliminate bacteria but do not address the underlying hyperkeratinization, sebaceous hyperactivity, or dysregulated innate immunity.

• Puberty and Androgens (Primary Trigger): The onset of acne coincides precisely with the rise in circulating androgens during Tanner stage 3-4 development. Dihydrotestosterone (DHT), the most potent androgen, is produced locally in sebaceous tissue via 5-alpha reductase activity and is the primary driver of sebaceous hyperplasia and increased lipogenesis. Conditions of androgen excess (polycystic ovary syndrome [PCOS], congenital adrenal hyperplasia [CAH], androgen-secreting tumors, or iatrogenic androgen use) universally produce or exacerbate acne. Conversely, androgen receptor blockade with spironolactone or finasteride improves acne, confirming the androgen dependence of the condition.

• Genetic Predisposition: Twin and family studies demonstrate concordance rates exceeding 50% for monozygotic twins versus 20% for dizygotic twins, establishing a strong genetic component. Specific polymorphisms in genes regulating sebaceous gland function, innate immunity (TLR variants), and androgen sensitivity (androgen receptor gene CAG repeats) correlate with acne severity. Family history of severe acne is a significant risk factor for developing nodulocystic disease.

• Dietary Factors (Emerging Evidence): High-glycemic-index carbohydrates increase insulin and IGF-1 levels, which stimulate androgen production in the adrenal glands and ovaries and enhance sebaceous lipogenesis. Dairy products, particularly milk (containing growth hormones and IGF-1), have been epidemiologically associated with acne severity in prospective studies, though causation remains incompletely established. Iodine-rich foods (seaweed, shellfish) may exacerbate inflammatory acne through immune activation.

• Medications (Secondary Acne Triggers): Lithium (increases follicular hyperkeratinization and pro-inflammatory cytokines), corticosteroids (systemic and topical, though less commonly topical), anabolic steroids and androgens, tetracyclines (photosensitivity leading to inflammation), phenytoin, and azathioprine are documented acnegenic. Oral contraceptive pills containing androgenic progestins (levonorgestrel, norgestrel) may worsen acne, while pills with anti-androgenic progestins (drospirenone, desogestrel) improve it.

• Environmental and Mechanical Factors: Occlusive products and comedogenic cosmetics (rated 0-5 on comedogenicity scale) trap sebum and bacteria; high humidity and sweating increase follicular occlusion and bacterial proliferation; friction from tight clothing or straps ("acne mechanica") ruptures comedones. Chlorine exposure (from swimming pools) may irritate follicular epithelium.

• Psychological Stress: Stress elevates CRH and activates the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system, increasing sebaceous production and follicular hyperkeratinization. Prospective studies document acne flares during periods of high stress.

• Smoking: Paradoxically, smoking may be protective against inflammatory acne (possibly via suppression of innate immunity) but is associated with increased comedonal acne and decreased treatment response.

• Comedones (Non-Inflammatory Acne): Blackheads (open comedones) appear as 1-3 mm dark papules on the face (especially nose, forehead, and chin) with a central dark plug; the dark appearance is due to oxidation and melanin, not dirt. Whiteheads (closed comedones) present as small (1-2 mm) skin-colored to yellowish papules without a central opening; they are more difficult to treat because the follicular opening is sealed, trapping keratin and sebum. Comedones are the most common lesion type and predominate in non-inflammatory and mild acne.

• Inflammatory Lesions: Papules are erythematous, dome-shaped lesions (2-5 mm) representing follicular rupture with localized dermal inflammation and neutrophil infiltration. Pustules are papules with a central collection of purulent material (neutrophils, bacteria, and cellular debris) visible as a yellow-white center, indicating more intense follicular inflammation. Nodules are large (>5 mm), firm, tender subcutaneous inflammatory lesions extending deep into the dermis and subcutis, representing chronic inflammation and fibrosis; they may persist for weeks to months. Cysts are fluctuant nodular lesions (>5 mm) containing purulent material; true cysts are lined by epithelium, though clinically the term is often applied to large nodules. Inflammatory lesions correlate with the presence of ruptured follicles and increased intrafollicular Cutibacterium acnes load.

• Distribution Pattern: Acne classically affects the T-zone (forehead, nose, chin) due to highest sebaceous gland density on the face, but can extend to cheeks, jaw, neck, chest, shoulders, and upper back. In women, acne may be distributed along the jawline and lower face (hormonally responsive "hormonal acne"). Severe nodular acne typically involves the lower face and neck.

• Associated Symptoms: Lesions are usually asymptomatic but may be tender (especially nodules due to inflammatory edema and nerve involvement), pruritic (from histamine release by mast cells), or painful with manipulation. Patients often report post-inflammatory erythema and hyperpigmentation following lesion resolution.

• Severity Grades and Clinical Variants:
• Mild acne: Predominantly comedonal with few papules; <20 lesions total
• Moderate acne: Mix of comedones and papules/pustules; 20-100 lesions
• Severe acne: Numerous papules, pustules, nodules, and/or cysts; >100 lesions or presence of nodules
• Nodulocystic acne: Extensive nodules and cysts with potential for severe permanent scarring; highest risk for psychological morbidity
• Acne fulminans: Rare, explosive form with fever, arthralgias, and hepatosplenomegaly; often triggered by isotretinoin initiation in predisposed individuals
• Gram-negative folliculitis: Acne-like pustules caused by gram-negative rods (following prolonged antibiotic use) with minimal comedones
• Conglobata acne: Severe type with interconnecting cysts and sinus tracts, predominantly in males, with significant scarring

• Clinical Diagnosis (History and Physical Examination): Diagnosis is clinical, based on morphologic identification of characteristic lesions (comedones, papules, pustules, nodules, cysts) in a patient with typical age of onset (adolescence) and characteristic distribution. The history should specifically address onset age, progression, previous treatments and response, menstrual history in females (irregular cycles suggesting PCOS), systemic symptoms (fever, joint pain suggesting acne fulminans), and medication use. Physical examination should characterize lesion types and count, assess for signs of androgen excess (hirsutism, male-pattern baldness, clitoromegaly), evaluate for post-inflammatory hyperpigmentation or scarring, and examine for associated conditions.

• Acne Grading Scales: The Global Acne Grading Scale (GAGS) is the most validated system and multiplies lesion counts in specific facial regions (forehead, right cheek, left cheek, nose, chin, upper chest) by a factor (1 for comedones, 2 for papules/pustules, 3 for nodules) to generate a total score: <11 (mild), 11-18 (mild-moderate), 19-30 (moderate), 31-38 (moderate-severe), >38 (severe). This scale provides standardized assessment for research and clinical tracking.

• Laboratory Testing—Indication-Dependent: Routine laboratory testing is not indicated for uncomplicated acne. However, specific clinical scenarios warrant investigation:
• Acne in females with signs of androgen excess (irregular menses, hirsutism, male-pattern baldness): Measure total testosterone (normal <70 ng/dL), free testosterone (normal <2 ng/dL), and DHEA-S (normal 35-430 µg/dL). Elevated levels (>100 ng/dL total testosterone or >4 ng/dL free testosterone) suggest PCOS or other hyperandrogenic disorder requiring workup.
• Suspected PCOS (acne + irregular menses + obesity): GAGS score, pelvic ultrasound, and metabolic testing (fasting glucose, insulin, lipid panel).
• Pre-isotretinoin baseline: Liver function tests (AST, ALT), lipid panel (total cholesterol, LDL, HDL, triglycerides), and baseline pregnancy test (serum or urine β-hCG) in all females of childbearing potential. Isotretinoin is teratogenic (category X), requiring monthly pregnancy tests and two forms of contraception.

• Differential Diagnosis Considerations:
• Rosacea: Occurs in older individuals (>30 years), lacks comedones, features prominent flushing/erythema, and responds to different treatments
• Perioral dermatitis: Perioral distribution, excludes central face, often triggered by topical steroids
• Folliculitis: Bacterial folliculitis is diffuse, non-comedonal, and typically pruritic/painful; can coexist with acne
• Keratosis pilaris: Rough, follicular lesions primarily on extensor surfaces (arms, legs), non-inflammatory
• Drug-induced acneiform eruptions: History of inciting agent (lithium, steroids, androgens) with non-comedonal papules and pustules

• Mild Acne (Predominantly Comedonal)—First-Line Treatment:
• Topical Retinoids (Gold Standard): Tretinoin (0.025%-0.1% cream or gel), adapalene (0.1% or 0.3% gel/lotion), and tazarotene (0.05%-0.1% gel/cream) normalize follicular keratinization and reduce comedone formation by binding retinoid acid receptors (RAR-α, RAR-β, RAR-γ) and retinoid X receptors (RXR) on keratinocytes. Mechanism involves increased cell turnover, decreased intracellular adhesion, and upregulation of anti-inflammatory genes. Adapalene is better tolerated (less irritating, minimal systemic absorption) and is considered first-line for most patients. Initiate at lowest concentration (adapalene 0.1%) and increase to 0.3% if tolerated. Apply

Complications of the disease itself

• Permanent scarring: dermal collagen destruction from ruptured follicles and neutrophilic inflammation yields ice-pick, boxcar, and rolling atrophic scars; hypertrophic and keloid scars predominate on the trunk and jawline and in darker skin types. Signaled by textural change persisting after lesions resolve — its risk is the main argument for early aggressive therapy in nodulocystic disease (AAD acne guideline).
• Post-inflammatory hyperpigmentation and erythema: melanocyte stimulation and dermal vascular ectasia after inflammation; more prominent and longer-lasting in skin of color. Distinguish from active lesions — flat macules, not palpable papules.
• Psychosocial morbidity: depression, anxiety, social withdrawal, and suicidal ideation are documented with severe acne; screening for mood symptoms is appropriate at every visit. Active suicidal ideation is an emergency.
• Acne fulminans: abrupt ulcerative nodules with fever, arthralgias, leukocytosis, and elevated ESR — often precipitated by rapid isotretinoin initiation. Treat urgently with systemic corticosteroids, deferring or reducing isotretinoin until inflammation is controlled.
• Gram-negative folliculitis: monomorphic pustules emerging after prolonged oral antibiotics, reflecting selection of Klebsiella, Proteus, or Pseudomonas; classically responds to isotretinoin.

Complications of therapy

• Isotretinoin teratogenicity: retinoid embryopathy (craniofacial, cardiac, CNS defects). Pregnancy on isotretinoin is an emergency requiring immediate discontinuation and counseling; the FDA iPLEDGE REMS mandates two contraceptive methods and monthly pregnancy testing.
• Isotretinoin hypertriglyceridemia: markedly elevated triglycerides can precipitate acute pancreatitis — an emergency; monitor lipids and transaminases.
• Pseudotumor cerebri: headache, papilledema, and vision change; risk rises with concurrent isotretinoin plus a tetracycline, so the combination is avoided.
• Tetracycline-class effects: pill esophagitis, photosensitivity, tooth staining (avoid under age 8 and in pregnancy, per AAP), and with minocycline drug-induced lupus, DRESS, and slate-gray pigmentation.
• **Antibiotic resistance and C. difficile colitis**: mitigated by pairing antibiotics with benzoyl peroxide and limiting oral courses.
• Spironolactone hyperkalemia and combined oral contraceptive venous thromboembolism (ACOG medical eligibility framework).

• The organism: Cutibacterium acnes (formerly Propionibacterium acnes) is a gram-positive anaerobic rod — the same organism blamed for indolent prosthetic shoulder joint and neurosurgical shunt infections. Examiners like this crossover.
• The buzzword trap: a blackhead is dark from oxidized melanin and lipid, not dirt or poor hygiene. Scrubbing does not treat acne and worsens irritation.
• The backbone drug: a topical retinoid (adapalene) belongs in nearly every regimen because it is the only class that reverses follicular hyperkeratinization and prevents microcomedone formation — the precursor of all lesions (AAD acne guideline). Antibiotic monotherapy is the classic wrong answer.
• Always pair an antibiotic with benzoyl peroxide: BPO is a nonspecific oxidizer to which C. acnes does not develop resistance, so it suppresses emergence of resistant strains. Warn about bleaching of towels and clothing.
• Single best next step in severe nodulocystic or scarring acne: oral isotretinoin, after baseline lipids, transaminases, and pregnancy testing, with enrollment in the iPLEDGE REMS — two pregnancy tests before starting, two forms of contraception, and monthly testing. All ACE inhibitors and isotretinoin share the theme of absolute pregnancy contraindication.
• Do not combine isotretinoin with a tetracycline — additive risk of pseudotumor cerebri (headache, papilledema, diplopia from CN VI palsy).
• The hormonal association tested: acne plus irregular menses, hirsutism, or androgenic alopecia = evaluate for PCOS (total/free testosterone, DHEA-S). Otherwise, no labs. Spironolactone (androgen-receptor blockade) and combined oral contraceptives are the targeted therapies in women.
• The common distractor: rosacea — older patient, central-face flushing and telangiectasias, and no comedones. If comedones are absent and the patient is over 30, rethink the diagnosis; monomorphic pustules after prolonged antibiotics suggest gram-negative folliculitis, and perioral papules after topical steroids suggest perioral dermatitis.