Acne vulgaris !
A very common skin disease of hair follicles and oil glands that causes blackheads, whiteheads, pimples and sometimes deep painful lumps and scars.
Updated 2026-11-01
Structures involved
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In embryology
In the clinical exam
Why it happens
- Testosterone and its actions
- Hair follicles, sebaceous and sweat glands, nails
- Glands: exocrine vs endocrine, secretion types
What it is
A chronic inflammatory disease of the pilosebaceous unit (hair follicle and sebaceous gland) that produces comedones, papules, pustules and, in severe cases, nodules and cysts, mainly on the face, chest and back.
Who gets it
Affects most adolescents to some degree and often persists into adulthood, especially in women. In Latin American populations with darker skin types, post-inflammatory hyperpigmentation is a frequent and distressing sequel.
Causes
- Androgen-driven increase in sebum production
- Abnormal keratinisation that plugs the follicle (microcomedone)
- Proliferation of Cutibacterium acnes in the plugged follicle
- Inflammation in and around the follicle
Risk factors
- Puberty and family history
- Hyperandrogenism (polycystic ovary syndrome, congenital adrenal hyperplasia)
- Drugs: corticosteroids, anabolic steroids, lithium, some anticonvulsants
- Occlusive cosmetics and friction (acne mechanica)
- High-glycaemic diet and dairy may worsen it in some people
Pathophysiology
Androgens enlarge sebaceous glands and increase sebum. Keratinocytes in the follicle shed abnormally and form a plug (closed comedone, or open comedone when the pore dilates and the content oxidises). C. acnes thrives in this sebum-rich, low-oxygen space and triggers innate immune and inflammatory pathways; rupture of the follicle wall into the dermis causes inflamed papules, pustules and nodules, which may heal with scars.
Classification
- Comedonal (non-inflammatory) acne
- Mild to moderate papulopustular acne
- Severe nodular or nodulocystic acne
- Special forms: acne conglobata, acne fulminans, drug-induced acne
Symptoms and signs
- Open comedones (blackheads) and closed comedones (whiteheads)
- Red papules and pustules on the face, chest, shoulders and back
- Deep tender nodules and cysts in severe acne
- Scars (ice-pick, boxcar, hypertrophic) and post-inflammatory dark marks
- Low self-esteem, anxiety or depression
Diagnosis
- Clinical
- Clinical: lesion types (comedones are the hallmark), distribution and severity, scarring and psychological impact; drug and menstrual history.
- Tests
- Usually none. Androgen testing (total and free testosterone, DHEA-S) and other tests when hyperandrogenism is suspected. Before and during isotretinoin: pregnancy tests and, by local protocol, lipids and liver enzymes.
- Imaging
- Not needed; pelvic ultrasound only if polycystic ovary syndrome is being evaluated.
Differential diagnosis
- Rosacea (no comedones, flushing, telangiectasia)
- Perioral dermatitis
- Bacterial or Malassezia (pityrosporum) folliculitis
- Drug-induced (steroid) acneiform eruption
- Hidradenitis suppurativa
Goal of treatment
Control lesions, prevent scars and pigment marks, and reduce psychological burden, choosing treatment by severity and limiting antibiotic use to avoid resistance.
Treatment
- Medical
- Topical retinoids (adapalene, tretinoin) for comedones and as maintenance, with benzoyl peroxide and azelaic acid; topical antibiotics such as clindamycin are always combined with benzoyl peroxide to limit resistance.
- Medical
- Moderate to severe inflammatory acne: oral tetracyclines (doxycycline, minocycline) for a limited time with a topical retinoid and benzoyl peroxide; tetracyclines are avoided in pregnancy and young children and cause photosensitivity. In women, combined oral contraceptives or spironolactone act on androgens.
- Medical
- Oral isotretinoin for severe nodular, scarring or refractory acne. It is highly teratogenic: a pregnancy-prevention programme with two forms of contraception and repeated negative pregnancy tests is mandatory, and people on it must not donate blood or share the drug.
- Follow-up
- Nursing and medical monitoring on isotretinoin: pregnancy tests, lipids and liver enzymes per protocol, mood and suicidal thoughts, dry skin, lips and eyes, and sun protection.
- Lifestyle
- Gentle non-comedogenic skin care, not picking or squeezing lesions, and daily sun protection to limit dark marks.
Complications
- Permanent atrophic or hypertrophic scars and keloids
- Post-inflammatory hyperpigmentation, common in darker skin
- Depression, anxiety and social withdrawal
- Birth defects if isotretinoin is taken during pregnancy (retinoid embryopathy) and pregnancy loss
Prognosis
Usually improves after adolescence but can persist for years. Early effective treatment prevents most scarring; isotretinoin gives long remission in most people with severe acne.
Prevention
- Early treatment of inflammatory acne to prevent scars
- Non-comedogenic cosmetics and avoiding picking
- Strict pregnancy prevention during and after isotretinoin treatment for the advised period
Test yourself
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What are the four key factors in the pathogenesis of acne?
Increased sebum (androgens), follicular hyperkeratinisation, Cutibacterium acnes and inflammation.
What is the hallmark lesion that separates acne from rosacea?
The comedone (blackhead or whitehead); rosacea has no comedones.
Why are topical antibiotics combined with benzoyl peroxide in acne?
To reduce the emergence of resistant bacteria.
What is the most important safety measure with isotretinoin?
Strict pregnancy prevention (two contraceptive methods and repeated negative pregnancy tests) because the drug is highly teratogenic.
Which oral antibiotic class is used for moderate inflammatory acne and in whom is it avoided?
Tetracyclines such as doxycycline; avoided in pregnancy and in young children because of tooth and bone effects.
Related conditions
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Acne (MedlinePlus (U.S. National Library of Medicine), 2024); Isotretinoin (MedlinePlus (U.S. National Library of Medicine), 2024).
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Representative model, for educational purposes only.
