Malassezia

Malassezia (formerly Pityrosporum) is a yeast that lives on normal skin, mainly oily areas. It is the most common fungus on human skin; fungi make up only 1–5% of the skin microbiota (Acta Derm Venereol 2020). Because it is always present, finding it on skin scrapings does not diagnose anything (DermNet, Seborrhoeic dermatitis). Its lipases break down sebum into free fatty acids, which may inflame the skin.

Malassezia [part-of] Skin Microbiome Malassezia [relates] Seborrhoeic Dermatitis

Cradle cap and seborrhoeic dermatitis. Malassezia is implicated in Seborrhoeic Dermatitis and cradle cap, together with oil glands still stimulated by the mother’s hormones. Its exact role is unclear (DermNet, Cradle cap 2017). Because it heavily colonises sebum-rich skin, anti-yeast treatment such as ketoconazole 2% cream is often used for long-term control, while a mild steroid or TCI calms a flare quickly (Siegfried & Hebert 2015). Some strains resist azoles, so zinc pyrithione or selenium sulphide are alternatives in adults (DermNet). Cradle cap peaks at 3 months and usually settles by 12 months, so a yeast-driven rash is uncommon in toddlers. DermNet advises reconsidering the diagnosis if “cradle cap” persists beyond 12 months; Atopic Dermatitis and Psoriasis are the main alternatives.

Malassezia [causes] Seborrhoeic Dermatitis Seborrhoeic Dermatitis [relates] Atopic Dermatitis

Role in atopic dermatitis. In AD, Malassezia acts more as an allergen than as an infection. People with AD are more often IgE-sensitised to M. furfur than the general population (Acta Derm Venereol 2020). A protein from M. globosa, MGL_1304, is the main allergen in human sweat. It triggers histamine release from the blood cells of most AD patients tested (Hiragun, JACI 2013), which helps explain why Heat and Sweat make itch worse. Fungal studies of AD skin come mostly from adults and Asian populations, so there are no toddler-specific data.

Malassezia [triggers] Atopic Dermatitis Malassezia [relates] Heat and Sweat Malassezia [relates] Th2 Immune Response

Other links. A Malassezia metabolite (pityriacitrin) blocks pigment production and is one unproven explanation for Pityriasis Alba (DermNet 2020). Widespread Malassezia infections, like tinea, occur more often in AD because the skin’s antimicrobial barrier is weaker (Elias & Wakefield 2011).

Malassezia [relates] Pityriasis Alba Skin Barrier Dysfunction [relates] Malassezia

Connections

• Seborrhoeic Dermatitis — implicated yeast; ketoconazole target, source: DermNet 2017
• Heat and Sweat — Malassezia globosa protein MGL_1304 is the main sweat allergen in AD, source: Hiragun 2013
• Pityriasis Alba — proposed (unproven) role of Malassezia metabolite in hypopigmentation, source: DermNet 2020
• Skin Microbiome — commonest skin fungus, 1–5% of microbiota, source: Acta Derm Venereol 2020
• Atopic Dermatitis — IgE sensitisation to Malassezia more common in AD, source: Acta Derm Venereol 2020
• Skin Barrier Dysfunction — weak antimicrobial barrier allows Malassezia infection, source: Elias & Wakefield 2011