Malassezia Infections

Microbiology and Lipid-Dependent Pathogenesis

A Lipid-Dependent Organism

Almost all Malassezia species (except Malassezia pachydermatis) lack the genes needed to make their own long-chain fatty acids. They therefore depend entirely on external lipids from the host's sebaceous glands.

• Common species: Malassezia globosa (the leading cause of tinea versicolor and dandruff), Malassezia restricta (predominant in seborrheic dermatitis), Malassezia sympodialis and Malassezia furfur.

How It Causes Inflammation and Pigment Changes

• Breakdown of lipids into free fatty acids: the yeast secretes lipases and esterases that split sebum triglycerides into free fatty acids (such as oleic and arachidonic acid). These damage the skin barrier and prompt keratinocytes to release inflammatory cytokines such as IL-1α, IL-6 and TNF-α, causing redness, scaling and itch.
• Why tinea versicolor causes pale patches: Malassezia produces dicarboxylic acids, especially azelaic acid. This directly inhibits tyrosinase in melanocytes and is toxic to them, interrupting melanin production and leaving off-white patches of reduced or lost pigment.
• Why patches can darken: in some cases, inflammation triggered by the yeast enlarges the melanosomes, and a thickened scale layer scatters light, producing patches that range from light brown to blue-black.

Clinical Forms of Malassezia Disease

Tinea Versicolor (Pityriasis Versicolor):

• Appearance: patches or papules in varying colors (white, pink, brown, gray) covered with a fine, powdery scale. Gently stretching or scraping the surface makes the scale lift off clearly (Besnier's sign, or the "wood-shaving" sign).
• Location: mainly the back, chest, neck and upper arms, where sebaceous glands are concentrated. Patients often notice mild itch or prickling when they sweat.

Malassezia (Pityrosporum) Folliculitis: Often mistaken for ordinary acne (acne vulgaris).

• Appearance: uniform small red papules and pustules (2–4 mm) centered on hair follicles, with no comedones. Patients often complain of intense itching and burning on the chest and back, worse in hot, humid weather or after sweating.

Seborrheic Dermatitis:

• Appearance: poorly defined pink-red patches covered with greasy yellow scale or dry white flakes.
• Location: the scalp (heavy dandruff), eyebrows, nasolabial folds, behind the ears and the center of the chest. It is chronic, with flares linked to stress, cold dry weather or weakened immunity.

Head and Neck Atopic Dermatitis: here Malassezia acts as an allergen. The body produces specific IgE antibodies against Malassezia proteins, setting off chronic red, burning, dry and scaly eczema on the face, neck and scalp in adults.

Differential Diagnosis

How We Diagnose It at Haute-Derma

Wood's Lamp Examination: performed in a darkened room. Tinea versicolor caused by Malassezia glows coppery-yellow, ivory-yellow or pale green because of the metabolite pityrialactone. This reveals the true edges of lesions that cannot yet be seen with the naked eye.

Digital Dermoscopy:

• Tinea versicolor: well-defined hypopigmented patches with fine scale concentrated along the natural skin creases.
• Malassezia folliculitis: a pink halo around the follicle opening, with coiled hairs or hairs blocked by a keratin plug containing a tiny pustule.

20% KOH Microscopy with Parker Ink or Calcofluor White Staining:

• Skin scrapings or pus from a follicle are placed on a slide.
• Under the microscope, the classic "spaghetti and meatballs" picture appears: short, straight or slightly curved hyphae mixed with clusters of round, thick-walled yeast cells.

Culture on Lipid-Enriched Media: because Malassezia does not grow on standard Sabouraud agar, the Haute-Derma laboratory uses modified Dixon agar or Leeming-Notman agar (containing olive oil and Tween 80) to isolate the species in treatment-resistant cases.

Comprehensive Treatment at Haute-Derma

Topical Antifungal Therapy

Used for limited tinea versicolor, mild seborrheic dermatitis, or as maintenance alongside other treatment:

• Medicated antifungal body washes and shampoos:
  • Ketoconazole 2% or selenium sulfide 2.5%: use as a body wash or shampoo 2–3 times a week. Apply evenly to the affected skin (chest, back, scalp) and leave on for 5–10 minutes before rinsing, so the active ingredient can penetrate the stratum corneum.
  • Zinc pyrithione 1%–2% or ciclopirox olamine 1%: alternate daily.
• Antifungal creams and gels:
  • Ketoconazole 2%, terbinafine 1%, econazole 1% or sertaconazole 2% cream: apply 1–2 times a day for 2–3 weeks.
  • A cleansing gel with 2% salicylic acid loosens scale, clears the follicle openings and helps antifungals penetrate.

Systemic Antifungal Therapy

Used for Malassezia folliculitis, widespread tinea versicolor, or when topical treatment has failed:

• Itraconazole (first choice):
  • Dose: 200 mg once daily, taken right after a fatty meal, for 7–14 days.
• Fluconazole:
  • Dose: 300 mg once a week for 2–3 weeks (or 150 mg daily for 14 days).
• Important: oral terbinafine is NOT effective against Malassezia (although topical terbinafine has a mild effect). Oral terbinafine should therefore never be prescribed for Malassezia-related conditions.

Environmental Hygiene and Relapse Prevention

• Maintenance therapy: once the skin has cleared, continue washing with ketoconazole 2% or selenium sulfide shampoo once a week throughout the hot, humid summer months.
• Oil control: products with niacinamide or salicylic acid, or in-clinic phototherapy, help reduce excess sebum.
• Personal hygiene: wash clothing and towels in water above 60°C, and avoid tight synthetic clothing that does not wick sweat.