Skin infections: the biopsy
- Lesion
Common skin infections by viruses, bacteria and fungi each leave a recognisable mark in the skin sample.
What it is
Viral, bacterial and fungal infections of the epidermis are frequent, mostly in children and in people with weak immunity. Human papillomavirus causes warts with koilocytes; molluscum contagiosum poxvirus fills keratinocytes with large inclusion bodies; Staphylococcus aureus and Streptococcus pyogenes cause impetigo, with a superficial split in the bullous form; dermatophytes and Malassezia live in the stratum corneum, where special stains reveal them.
What each infection looks like under the microscope
| Infection | Agent | Key finding |
|---|---|---|
| Common wart | HPV | Papillomatosis, hyperkeratosis, koilocytes, coarse keratohyalin granules |
| Molluscum contagiosum | Molluscum contagiosum virus (poxvirus) | Cup-shaped lesion full of molluscum bodies |
| Bullous impetigo | S. aureus exfoliative toxin | Subcorneal blister with neutrophils, Gram-positive cocci |
| Tinea (dermatophytosis) | Trichophyton and other dermatophytes | Hyphae in stratum corneum on PAS |
| Pityriasis versicolor | Malassezia | Short hyphae and yeasts in stratum corneum |
| Cutaneous candidiasis | Candida albicans | Pseudohyphae and yeasts with subcorneal pustules |
Clinical notes
- Many or giant molluscum lesions in an adult suggest HIV infection.
- Post-streptococcal glomerulonephritis can follow impetigo; rheumatic fever does not.
- Extensive, persistent warts suggest immunodeficiency; epidermodysplasia verruciformis carries a skin cancer risk.
Test yourself
Think of the answer, then tap the question to see it.
What is a koilocyte?
A keratinocyte infected by HPV with an enlarged, wrinkled, hyperchromatic nucleus and a perinuclear halo.
How does bullous impetigo produce a blister?
S. aureus exfoliative toxin cleaves desmoglein 1, causing a subcorneal split.
Where are dermatophytes found in a skin biopsy?
In the stratum corneum, best seen with PAS or silver stains.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Skin Infections (MedlinePlus, US National Library of Medicine, 2025); Warts (MedlinePlus, US National Library of Medicine, 2025); Impetigo (MedlinePlus, US National Library of Medicine, 2025); Tinea Infections (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.