Piedra: Causes, Diagnosis, And Effective Treatments

Piedra is a superficial fungal infection of the hair shaft characterised by small

black

or

white

nodules firmly attached along the hair. The name ‘piedra’ means ‘stone’ in Spanish, reflecting the hard, stone-like appearance of these fungal deposits.

Also known as trichomycosis nodosa or trichomycosis nodularis, piedra primarily affects scalp hair but can involve facial, axillary, pubic, and leg hair. It remains largely asymptomatic, causing no pain or itch, though it may lead to hair breakage if untreated.

Who gets piedra?

There is limited epidemiological data on the

incidence

and

prevalence

of piedra globally. It is more common in

tropical

and

subtropical

regions, including parts of South America, Africa, India, and Southeast Asia, due to favourable humid conditions for fungal growth.

Piedra affects individuals of all ages, genders, and ethnicities, with no strong racial or skin type predispositions documented. However, certain practices increase risk:

• Infrequent hair washing or poor hygiene
• Use of hair oils or pomades
• Bathing in contaminated stagnant water, rivers, or soil
• Wearing occlusive head coverings like turbans, hijabs, or wigs that trap moisture
• Beard or pubic hair in humid environments

Children and women in endemic areas may present more frequently, with white piedra reported in paediatric cases.

Causes

Piedra results from infection by specific fungi that colonise the hair keratin. There are two distinct types:

Black piedra

Caused by Piedraia hortae, a dematiaceous (pigmented) fungus. Black piedra nodules are hard, dark brown-to-black, and tightly adherent to the hair shaft, often encircling it completely. The fungus produces ascospores within the nodules.

White piedra

Caused by Trichosporon species, primarily T. inkin (genital/axillary hair), T. ovoides (scalp), or T. asahii. These yeasts form soft, white-to-light brown, loosely attached nodules, typically at the hair tips. Trichosporon is ubiquitous in soil, water, air, vegetation, and human flora.

Infection occurs via direct contact with contaminated sources. Fungi thrive in warm, moist conditions, adhering to hair cuticle and forming biofilms. Person-to-person transmission is rare but possible via shared combs, towels, or sexual contact for genital white piedra.

Clinical features

The hallmark of piedra is

discrete nodules

(1–3 mm diameter) along single or multiple hair shafts. They may cluster, giving a beaded appearance.

Feature	Black Piedra	White Piedra
Colour	Black/dark brown	White/gray/tan
Texture	Hard, gritty, adherent	Soft, loosely attached
Location	Scalp, beard (tropics)	Scalp, pubic, axillary, beard
Size/Shape	Ovoid, encircling shaft	Round, tip-focused clusters
Hair Damage	Minimal breakage	Brittle, splitting on removal

Piedra is asymptomatic—no pain, itch, or inflammation. A key diagnostic clue is a

negative hair pull test

: hairs do not extract easily from follicles, unlike tinea capitis. Advanced cases show matted hair or diffuse nodularity.

Skin type variations

No specific variations by

Fitzpatrick skin type

are reported, as piedra affects the hair shaft superficially, not the skin. However, in curly or Afro-textured hair, nodules may be harder to visualise amid coils. Oily hair types (common in Mediterranean/Asian populations) may predispose due to sebum favouring fungal adhesion.

Complications

Piedra is benign but chronic if untreated, persisting for years. Potential issues include:

• Hair breakage: Manual nodule removal weakens shafts, especially in white piedra
• Cosmetic distress: Visible nodules on scalp/beard
• Secondary bacterial infection: Rare, from scratching
• Recurrence: High in genital white piedra (T. inkin), up to 50% without hygiene measures

No systemic spread or scarring reported.

Diagnosis

Diagnosis is clinical, based on characteristic nodules. Confirm with:

• Microscopy: KOH mount shows fungal hyphae, arthroconidia (white piedra), or ascospores (black)
• Culture: Sabouraud agar grows Piedraia (slow, black colonies) or Trichosporon (yeasty)
• Wood lamp: Non-fluorescent, unlike tinea
• Biopsy: Rarely needed; shows cement-like matrix around hair

Differential diagnosis

• Trichobacteriosis (trichomycosis axillaris): Bacterial, white/yellow/red sheaths on axillary/pubic hair; dissolves in KOH
• Hair casts: White, cylindrical, slide freely; no fungi
• Monilethrix: Beaded hair genetically; uniform beading, no nodules
• Tinea capitis: Positive pull test, scaling, fluorescence
• Seborrhoeic dermatitis/dandruff: Flakes, not adherent
• Lice nits: Pearl-like, near scalp; detach easily

Treatment

Treatment is straightforward and highly effective. Options vary by type and site:

General measures

• Clip or shave affected hair: Curative, immediate
• Improve hygiene: Daily washing with antifungal shampoo
• Discard combs/towels; disinfect fomites

Topical antifungals (first-line)

• Black piedra: 2% selenium sulfide shampoo weekly × 4–6 weeks; or topical ciclopirox
• White piedra: Ketoconazole 2% shampoo/lotion, clotrimazole 1%, miconazole 2%; apply daily × 2–4 weeks

Oral antifungals (recalcitrant cases)

• Itraconazole 200 mg/day × 1–2 weeks or terbinafine 250 mg/day × 2 weeks

For pubic/axillary recurrence: Combine shaving + topical + partner treatment if sexual transmission suspected.

Prevention

Prevent via:

• Regular hair washing (daily in humid climates)
• Avoid oil/mineral oil overuse
• Comb hair regularly to disrupt biofilms
• Avoid stagnant water bathing
• Loose, breathable headwear
• Hygiene in shared facilities (gym, dorms)

Prognosis and outcome

Excellent with treatment: Resolution in weeks. Black piedra rarely recurs; white piedra (genital) may need ongoing prophylaxis. Untreated, persists chronically without harm beyond cosmetics. Early intervention prevents hair damage.

Frequently Asked Questions

Is piedra contagious?

Rarely; indirect via fomites or water, not casual contact.

Does piedra cause hair loss?

No, it affects shafts only; no follicular damage.

Can piedra affect eyelashes or eyebrows?

Yes, white piedra possible on facial hair.

How long does treatment take?

Shaving: immediate; topicals: 2–6 weeks.

Is piedra the same as white piedra only?

No, includes black and white variants.