Inflammatory lesions in acne
Inflammatory lesions in acne (pimples or zits) include small red bumps (papules), pustules, large red bumps (nodules) and cysts (these are fluctuant nodules). They are often painful.
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What is the cause of inflammatory acne?
They usually result from rupture of the wall of the closed comedone but may arise from normal-appearing skin.
The factors contributing to inflammation are:
- Bacteria Chemicals produced by Propionibacterium acnes diffuse into the surrounding skin (dermis) and attract white blood cells (polymorphonucleocytes and monocytes).
- Immunological reaction For unknown reasons, the cells lining the sebaceous ducts also produce inflammatory mediators (IL-1a, IL-b and tumour necrosis factor) so pimples may occur in the absence of bacteria.
- Foreign body reaction White blood cells (macrophages and giant cells) removing the debris may cause a more severe granulomatous inflammatory reaction.
- Irritation by lipids Free fatty acids and sebum penetrate the dermis after the duct has ruptured
- Hypersensitivity to P. acnes Hypersensitivity (allergy) to P. acnes is thought to be the cause of the severe skin condition, acne fulminans.