What Is Yeast Infection (Malassezia Dermatitis)?
Yeast infection in pets — most commonly caused by Malassezia pachydermatis — is an overgrowth of naturally occurring yeast on the skin and in the ears. It typically develops secondary to an underlying condition (allergies, skin fold anatomy, hormonal disorder) that disrupts the skin's normal environment. The hallmark signs are intense itching, redness, a musty or 'corn chip' odour, and dark greasy skin.
Understanding Yeast Infection (Malassezia Dermatitis)
Malassezia yeast is normally present on all dogs' skin in small numbers without causing disease. When the skin environment changes — increased moisture, disrupted pH, compromised immune function, or altered skin barrier from allergic inflammation — the yeast population can overgrow. Certain breeds with skin folds (Bulldogs, Shar Peis), pendulous ears (Spaniels, Basset Hounds), or a genetic predisposition to atopy (West Highland White Terriers, Golden Retrievers) are at significantly higher risk.
The most commonly affected areas are the ear canals, between the toes, in skin folds, under the tail base, and in the groin. In the ears, Malassezia causes dark brown waxy discharge, inflammation, and a distinctive yeasty odour. Chronic ear infections with Malassezia are one of the hallmark features of atopic dermatitis in dogs. Skin infections cause a greasy, reddened, thickened coat that darkens over time (hyperpigmentation) with a musty smell owners sometimes describe as 'Fritos' or corn chips.
Diagnosis is confirmed through cytology — a cotton swab or tape sample from the affected area is examined under a microscope to count Malassezia organisms. Treatment involves antifungal shampoos (chlorhexidine/ketoconazole), ear cleaners with antifungal agents, and in persistent or widespread cases, oral antifungal medication (ketoconazole or fluconazole). Critically, the underlying trigger must also be addressed — treating yeast without managing the allergy or anatomical cause leads to rapid recurrence.