Agents of superficial mycoses (Hortaea werneckii, Piedraia hortae, Trichosporon)
- Fungus
- For completeness
Fungi that live only on the dead outer layer of skin or on the hair shaft. They cause stains or nodules, not inflammation, and are easy to treat.
Also called: tinea nigra, black piedra, white piedra
Quick facts
- Type
- Fungus · Molds and dermatophytes
- Gram / shape
- Brown septate hyphae
- Spread
- Hortaea · Piedra
- Causes
- Tinea nigra · Black piedra · White piedra
- Treatment
- Tinea nigra
At a glance
- Shape
- Brown septate hyphae (tinea nigra); hard black or soft white nodules on hair (piedra)
- Family
- Hortaea and Piedraia: Ascomycota; Trichosporon: Basidiomycota
- Type
- Hortaea and Piedraia: pigmented molds; Trichosporon: yeast-like fungus
- Stain
- KOH of scrapings or hairs; culture on Sabouraud agar
Morphology
- Hortaea werneckii: brown, branched, septate hyphae in skin scrapings; black, waxy, yeast-like colonies at first.
- Piedraia hortae: hard black nodules glued to the hair shaft; the nodule holds asci with ascospores.
- Trichosporon spp.: soft whitish nodules that slide along the hair; arthroconidia and blastoconidia; cream, wrinkled (cerebriform) colonies.
Transmission
- Hortaea: contact of the skin with soil, wood or salty environments; minor trauma helps; sweating of palms favors it.
- Piedra: hair contact with fungi from soil and water; long wet hair kept covered or tied up favors it.
- Not usually spread from person to person in a way that matters clinically.
Reservoir: Soil, decaying plant matter and salty or brackish environments (Hortaea); Soil and water in tropical regions (Piedraia, Trichosporon)
Isolation precautions
What the care team adds to standard precautions.
- Standard
Virulence factors
- They stay in keratin (stratum corneum or hair cuticle), so the immune system hardly reacts: no itch, no redness.
- Melanin in Hortaea and Piedraia explains the dark color of the lesion or nodule.
- Piedraia and Trichosporon can weaken the hair shaft until it breaks.
Diseases it causes
- Tinea nigra: a painless brown-black macule on the palm or sole, usually one-sided and slowly growing.
- Black piedra: firm, gritty black nodules on scalp hair, mostly in humid tropics (South America, Southeast Asia).
- White piedra: soft white to light-brown nodules on scalp, beard, axillary or pubic hair.
Clinical picture
- Tinea nigra is common in children and young people with sweaty palms in hot, humid areas.
- Its main importance is that it can look like an acral melanoma or a nevus; dermoscopy and a KOH test avoid an unnecessary excision.
- White piedra nodules can be confused with lice nits; nits are firmly cemented eggs and do not slide.
Diagnosis
- Tinea nigra: KOH of scrapings from the edge shows pigmented septate hyphae; culture grows black colonies within about a week.
- Dermoscopy of tinea nigra: fine brown spicules or speckles without a melanocytic pattern.
- Piedra: hair examined under the microscope or by trichoscopy; culture identifies the species.
Treatment
Tinea nigra: topical azoles (such as ketoconazole, miconazole or clotrimazole), ciclopirox or keratolytics. Piedra: cutting or shaving the hair plus antifungal shampoos or lotions; oral terbinafine or itraconazole if topical treatment fails.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Drying hair well and not tying or covering it while wet.
- Not sharing combs or hair accessories.
- Washing and drying hands after work with soil or wood; controlling hyperhidrosis.
Test yourself
Think of the answer, then tap the question to see it.
Which fungus causes tinea nigra, and why does the lesion matter clinically?
Hortaea werneckii. The brown macule on the palm or sole can be mistaken for acral melanoma; KOH and dermoscopy settle it.
How do black and white piedra differ?
Black piedra (Piedraia hortae) makes hard, firmly attached black nodules; white piedra (Trichosporon) makes soft, white, easily detached nodules.
Why do superficial mycoses cause little or no inflammation?
They stay in dead keratin (stratum corneum or hair cuticle) and do not reach living tissue, so there is almost no immune response.
How can white piedra be told apart from head lice?
Nits are eggs cemented to one side of the hair; piedra nodules surround the shaft, slide along it, and show fungal elements on microscopy.
Connections
← Back to the group: Molds and dermatophytes
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: White piedra, black piedra, tinea versicolor, and tinea nigra: contribution to the diagnosis of superficial mycosis (Anais Brasileiros de Dermatologia (PMC), 2017); Tinea nigra (DermNet, 2024); Piedra (DermNet, 2024).
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Representative model, for educational purposes only.