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causes of acne vulgaris pathophysiology mechanisms
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I now have comprehensive information from the images and textbooks. Here is the full answer:
Skin Findings
All three images show moderate-to-severe acne vulgaris with a mixed comedonal and inflammatory pattern on both cheeks and jawline. The lesions include:
- Closed comedones (whiteheads) - small, skin-coloured dome-shaped bumps giving a "cobblestone" texture
- Inflammatory papules - raised, red, tender bumps (3-6 mm)
- Pustules - yellowish-white pus-filled lesions, some weeping/crusting
- Nodules - deeper, firm, violaceous/dusky-red lesions on the jawline
- Post-inflammatory hyperpigmentation (PIH) - flat brown-red macules from healed lesions
- Early atrophic scarring - shallow depressed areas on the mid-cheek
Causes of Acne Vulgaris
Acne is a chronic inflammatory disease of the pilosebaceous unit (hair follicle + sebaceous gland). Four major interacting mechanisms drive it:
1. Excess Sebum Production
Androgens (especially testosterone and DHEAS) stimulate sebaceous glands to produce more sebum. This is why acne surges at puberty and why men tend to have more severe disease. Sebum itself is not directly comedogenic but creates the right environment for bacterial proliferation.
2. Follicular Hyperkeratosis (Plugging)
Abnormal shedding and accumulation of keratinocytes blocks the follicular orifice. This forms the primary lesion - the comedo:
- Closed comedo (whitehead): blocked pore with no air access; precursor to all inflammatory lesions
- Open comedo (blackhead): dilated follicular opening with oxidized dark debris; less prone to inflammation (Harrison's 22E, p.434)
3. Cutibacterium acnes (Formerly P. acnes) Colonisation
This anaerobic bacterium thrives in the sebum-rich, oxygen-poor follicle. It:
- Hydrolyses sebum triglycerides into free fatty acids (which are highly irritating and proinflammatory)
- Activates toll-like receptors on follicular epithelium, triggering innate immune responses
- Releases proteases, lipases, and hyaluronidase that weaken the follicular wall (Harrison's 22E; Andrews' Diseases of the Skin)
4. Inflammation and Follicular Rupture
When the engorged comedo wall ruptures, oily and keratinous debris spills into the dermis, triggering a foreign-body inflammatory reaction - producing papules, pustules, nodules, and eventually scarring if deep enough.
Aggravating / Contributing Factors
| Factor | Mechanism |
|---|---|
| Androgens (puberty, PCOS, CAH, tumours) | Drive sebum overproduction |
| High-glycaemic diet | Raises insulin/IGF-1, stimulating sebaceous activity |
| Dairy (skim milk, whey protein) | Hormonal content may worsen acne |
| Stress | Stimulates adrenal androgen release |
| Mechanical friction | Chin straps, helmets, phone against face - irritates follicular epithelium |
| Comedogenic products | Certain cosmetics, hair oils block pores |
| Medications | Corticosteroids, progestin-only contraceptives, lithium, isoniazid, androgens |
| Hyperandrogenic states | PCOS, congenital adrenal hyperplasia, Cushing syndrome, virilising tumours |
| Beard area | Hair follicle trauma from shaving + trapped bacteria under beard hair worsens the picture in men |
(Andrews' Diseases of the Skin - Clinical Dermatology; Harrison's 22E)
What's Driving This Particular Presentation
Given this is a young man with bilateral cheek and jawline distribution with active papulopustules, nodules, and early scarring - the most likely drivers are:
- Androgen-driven seborrhoea (common in young adult males)
- C. acnes colonisation in the follicles (especially under beard hair where the microenvironment is more anaerobic)
- Comedonal plugging beneath the beard line
- Possibly a dietary or stress component
Important: This is a clinical impression based on the images. A dermatologist should examine the skin in person to confirm the diagnosis, rule out other conditions (e.g., folliculitis, rosacea, perioral dermatitis), and prescribe appropriate treatment - which at this severity (moderate-to-severe nodular acne) typically involves oral antibiotics + topical retinoid, or consideration of oral isotretinoin.
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