[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Skin](https://durgical.com/en/general-pathology/areas/skin/) › Skin infections: the biopsy # Skin infections: the biopsy - Lesion Common skin infections by viruses, bacteria and fungi each leave a recognisable mark in the skin sample. Updated Nov 12, 2026 ## Key points - Verrucae (HPV): vulgaris (hands), plana (flat, face), plantar and palmar, condyloma acuminatum (anogenital, HPV 6 and 11); papillomatosis, hyperkeratosis, koilocytes. - Koilocyte: keratinocyte with a wrinkled nucleus and perinuclear clearing from HPV. - Molluscum contagiosum: umbilicated pearly papules; molluscum (Henderson-Patterson) bodies, large eosinophilic cytoplasmic inclusions. - Impetigo: honey-coloured crusts (non-bullous) or flaccid blisters (bullous, S. aureus exfoliative toxin cleaves desmoglein 1, subcorneal split). - Dermatophytes (Trichophyton, Microsporum, Epidermophyton): hyphae in the stratum corneum on PAS or silver stain, the «sandwich sign». - Pityriasis versicolor (Malassezia): «spaghetti and meatballs» hyphae and yeasts; candidiasis in moist folds. ## 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](https://durgical.com/en/conditions/viral-warts/) | HPV | Papillomatosis, hyperkeratosis, koilocytes, coarse keratohyalin granules | | [Molluscum contagiosum](https://durgical.com/en/conditions/molluscum-contagiosum/) | Molluscum contagiosum virus (poxvirus) | Cup-shaped lesion full of molluscum bodies | | [Bullous impetigo](https://durgical.com/en/conditions/impetigo/) | S. aureus exfoliative toxin | Subcorneal blister with neutrophils, Gram-positive cocci | | [Tinea (dermatophytosis)](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/) | Trichophyton and other dermatophytes | Hyphae in stratum corneum on PAS | | [Pityriasis versicolor](https://durgical.com/en/conditions/pityriasis-versicolor/) | Malassezia | Short hyphae and yeasts in stratum corneum | | [Cutaneous candidiasis](https://durgical.com/en/conditions/cutaneous-and-mucocutaneous-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. ## Memory aid HPV leaves halos around nuclei (koilocytes), molluscum leaves big pink bodies, and fungi hide in the roof (stratum corneum) until PAS turns on the light. ## 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. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/skin-infections-the-biopsy/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Special stains in diagnosis: Congo red, Prussian blue, PAS, Ziehl–Neelsen, Gram](https://durgical.com/en/general-pathology/special-stains-in-diagnosis-congo-red-prussian-blue-pas-ziehl-neelsen-gram/) ## Connections ## Related 3 - [Actinic keratosis and squamous cell carcinoma](https://durgical.com/en/general-pathology/actinic-keratosis-and-squamous-cell-carcinoma/) - [Pemphigus](https://durgical.com/en/general-pathology/pemphigus/) - [Special stains in diagnosis: Congo red, Prussian blue, PAS, Ziehl–Neelsen, Gram](https://durgical.com/en/general-pathology/special-stains-in-diagnosis-congo-red-prussian-blue-pas-ziehl-neelsen-gram/) ## Related conditions 7 - [Viral warts (verruca)](https://durgical.com/en/conditions/viral-warts/) - [Molluscum contagiosum](https://durgical.com/en/conditions/molluscum-contagiosum/) - [Impetigo](https://durgical.com/en/conditions/impetigo/) - [Dermatophytosis (tinea) and onychomycosis](https://durgical.com/en/conditions/dermatophytosis-and-onychomycosis/) - [Pityriasis versicolor](https://durgical.com/en/conditions/pityriasis-versicolor/) - [Cutaneous and mucocutaneous candidiasis](https://durgical.com/en/conditions/cutaneous-and-mucocutaneous-candidiasis/) - [Staphylococcal scalded skin syndrome](https://durgical.com/en/conditions/staphylococcal-scalded-skin-syndrome/) ## Microorganisms 7 - [Human papillomavirus](https://durgical.com/en/microbiology/human-papillomavirus/) - [Molluscum contagiosum virus](https://durgical.com/en/microbiology/molluscum-contagiosum-virus/) - [Staphylococcus aureus](https://durgical.com/en/microbiology/staphylococcus-aureus/) - [Streptococcus pyogenes](https://durgical.com/en/microbiology/streptococcus-pyogenes/) - [Dermatophytes (Trichophyton, Microsporum, Epidermophyton)](https://durgical.com/en/microbiology/dermatophytes/) - [Malassezia](https://durgical.com/en/microbiology/malassezia/) - [Candida albicans](https://durgical.com/en/microbiology/candida-albicans/) [← All of general pathology](https://durgical.com/en/general-pathology/) 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](https://medlineplus.gov/skininfections.html) (MedlinePlus, US National Library of Medicine, 2025); [Warts](https://medlineplus.gov/warts.html) (MedlinePlus, US National Library of Medicine, 2025); [Impetigo](https://medlineplus.gov/impetigo.html) (MedlinePlus, US National Library of Medicine, 2025); [Tinea Infections](https://medlineplus.gov/tineainfections.html) (MedlinePlus, US National Library of Medicine, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/skin-infections-the-biopsy/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/skin-infections-the-biopsy/