Piedra

Classification and Microbiology

Piedra is divided into two distinct clinical forms, based on the organism, its ecology and the structure of the nodules:

Black Piedra:

• Cause: The ascomycete fungus Piedraia hortae (class Ascomycetes). It is common in hot, humid tropical regions such as Southeast Asia and South America.
• Nodule structure (stroma): Dark brown-black, thick-walled septate hyphae are tightly woven together and cemented to the hair shaft by a cement-like substance the fungus produces itself. The stroma contains asci that shelter the ascospores, allowing the fungus to survive harsh environmental conditions.

White Piedra:

• Cause: Yeasts of the genus Trichosporon, most often Trichosporon ovoides (scalp hair), Trichosporon inkin (groin and pubic hair) and Trichosporon asahii.
• Nodule structure: The fungus forms clusters of arthroconidia, blastoconidia and pseudohyphae. The nodules are softer, creamy white to pale yellow, more loosely attached around the shaft, and lack the dense cement-like matrix of Piedraia hortae.

How the hair shaft is damaged: Although neither fungus enters the follicle, both secrete extracellular keratinase. This enzyme gradually breaks down keratin in the cuticle and penetrates slightly into the cortex. The resulting weak spots where nodules attach make the hair prone to snapping or splitting during brushing or washing.

Clinical Features and Differential Diagnosis

Piedra is linked to hygiene habits, a persistently damp scalp, going to bed with wet hair, and frequent use of heavy hair oils that give fungal spores something to stick to.

Clinical Features of Black Piedra:

• Mainly affects scalp hair (rarely the beard or body hair).
• Dark brown to black nodules, from a few micrometers to 1–2 mm across, and very hard, like tiny stones to the touch.
• The nodules are firmly fixed, encircling the shaft completely, and cannot be slid off the hair. Patients often notice a strange crackling sound when combing or find that their hair feels rough.

Clinical Features of White Piedra:

• Can affect scalp hair, the beard, underarm hair and genital hair.
• Nodules are white, light gray or creamy yellow, soft, and larger than those of black piedra.
• They are more loosely attached and can easily be slid along the shaft. Patients usually complain of sticky, clumped hair with white specks that look like dandruff but do not fall off.

Differential Diagnosis Table

Our Diagnostic Process at Haute-Derma

To avoid confusing piedra with head lice nits or scaly scalp conditions, Haute-Derma follows a three-step workup:

• Dermoscopy (Trichoscopy):
  • Black piedra: black or dark brown nodules forming ring-like collars around the shaft, with a rough surface and visible widening of the shaft at each nodule.
  • White piedra: white or yellow sleeves wrapped unevenly around the shaft, with a fluffy or loose, slimy texture.
  • Telling it apart from nits: dermoscopy clearly shows an oval egg casing with a cap (operculum) and the louse embryo inside.
• Direct KOH Microscopy (10–20%):
  • A segment of hair carrying a nodule is placed in 10–20% KOH and gently warmed.
  • Black piedra: a dark stroma of thick septate hyphae. Closer inspection at the edge reveals asci containing 2–8 spindle-shaped ascospores with filament-like tails at each end.
  • White piedra: dense clusters of rectangular or oval arthroconidia and budding yeast cells (blastoconidia) mixed with pseudohyphae.
• Culture for Species Identification:
  • The sample is cultured on Sabouraud dextrose agar (SDA) at room temperature (25–30°C).
  • Important: when white piedra (Trichosporon spp.) is suspected, SDA containing cycloheximide must not be used, because cycloheximide can inhibit the growth of many Trichosporon species.

Personalized Treatment at Haute-Derma

Treatment has two goals: physically removing the fungal nodules from the hair and eradicating the fungus with topical or oral medication.

Cutting or Shaving Affected Hair (First-Line Mechanical Removal): This is the quickest, simplest and most effective treatment for both black and white piedra. Because the fungus does not enter the follicle, cutting off the affected lengths or shaving the area removes nearly all of the infection, usually without any need for oral medication.

Topical Treatment (For Patients Who Prefer Not to Cut Their Hair):

• Medicated antifungal shampoos:
  • Ketoconazole 2% or ciclopirox olamine 1.5%: lather evenly and leave on the scalp and hair for 10–15 minutes before rinsing. Use 3–4 times a week for 4–6 weeks.
  • Selenium sulfide 2.5% or zinc pyrithione 2%: used in rotation to help clear scale and fungal spores.
• Leave-on antifungal solutions/lotions:
  • Terbinafine 1% solution or luliconazole 1% lotion: apply directly to the affected hair once or twice daily after washing and drying.
• Soaks and rinses to loosen nodules:
  • Rinse the hair after shampooing with a dilute acetic acid solution (apple cider vinegar mixed 1:4 with warm water). The mildly acidic rinse softens the glucan cement of black piedra nodules, making them easier to comb off the shaft with a fine-tooth comb.

Oral Treatment (For Extensive Disease, Failure of Topicals or Repeated Reinfection):

• Itraconazole: 200 mg/day, taken after a fatty meal, for 1–2 weeks.
• Terbinafine: 250 mg/day for 2–4 weeks (particularly effective for black piedra).

Preventing Reinfection and Hair Hygiene:

• Never tie up your hair or go to bed while it is still damp; dry the scalp and hair completely after washing.
• Disinfect all hair-care items: combs, scissors, helmets, pillowcases and hair ties should be washed with an antimicrobial solution or soaked in boiling water or 70% alcohol.
• Cut back on hairsprays and heavy, waxy conditioners that leave hair sticky and trap moisture.