Malassezia infections

Malassezia yeasts are a type of fungus. The genus Malassezia is now thought to be composed of several different species. There is some controversy as to whether specific species cause different skin diseases. Species names include:

• M. dermatis
• M. equi
• M. furfur
• M. globosa
• M. obtusa
• M. pachydermatis
• M. restricta
• M. slooffiae
• M. sympodialis
• M. ovalis (also known as Pityrosporum ovale)

Skin conditions caused or aggravated by infection by malassezia include:

• Pityriasis versicolor – most often due to the subspecies M. globosa, M. sympodialis and M. furfur
• Malassezia folliculitis due to the yeast growing in the hair follicles where they produce inflammation
• Seborrhoeic dermatitis, dandruff, sebopsoriasis and facial or scalp psoriasis - – most often due to M. restricta and M. globosa.
• Neonatal cephalic pustulosis, a pustular eruption on young babies that resembles infantile acne
• Possibly, some cases of confluent and reticulated papillomatosis, a pigmented eruption occurring mainly on the chest, back and neck of adolescent girls
• Some facial atopic dermatitis; in this case there may be specific IgE antibodies directed against Malassezia and positive prick tests to the organism
• Rarely, invasive pityrosporosis in immunodeficient individuals.

Malassezia infections

Malassezia folliculitis

Pityriasis versicolor

Seborrhoeic dermatitis

Diagnosis

The diagnosis of malassezia infections is made from skin scrapings. Microscopy using potassium hydroxide (KOH) preparations shows clusters of yeast cells and long hyphae. The appearance is said to be like "spaghetti and meatballs". The hyphae filaments used to be called 'Malassezia' and the yeast forms were called 'Pityrosporum' but mycologists eventually realised they were the same organism.

Malassezia species are difficult to grow in the laboratory so scrapings may be reported as "culture negative". The yeast grows best if a lipid such as olive oil is added to Littman agar culture medium.

Predisposing factors to infection

Malassezia species inhabit the skin of about 90% of adults without causing harm. Unfortunately in some people the yeast suppresses the body's expected immune response to it allowing it to proliferate and cause a skin disorder, often without any inflammatory response.

Predisposing factors to Malassezia skin disease include:

• Humidity
• Sweating – hence pityriasis versicolor is common in tropical areas
• Oily skin – hence it is found mainly on scalp, face and upper trunk

The yeasts produce chemicals that reduce the pigment in the skin,causing whitish patches. These include azelaic acid, pityriacitrin and malassezin. Azelaic acid is however a useful treatment for some skin disorders such as acne and rosacea.

Malassezia may fluoresce on exposure to ultraviolet light e.g., a Wood's lamp. This is due to another chemical, pityrialactone.

Treatment

Consult DermNet's pages on the individual skin conditions to learn about treatment.

In general, malassezia infections are treated with topical or oral antifungal agents. Seborrhoeic dermatitis may also treated with topical steroids.