A type of yeast called Malassezia pachydermatis is commonly found on the skin and mucous membranes of healthy pugs. Normally, the yeast doesn't cause problems, but for unknown reasons it sometimes proliferates and causes a skin disease known as cutaneous malassezia or malassezia dermatitis. It's most often seen in dogs that live in humid areas and is characterized by greasy, itchy skin, increased pigmentation, and thickened or blackened skin, often in conjunction with ear infections or atopy. Affected areas usually include the face, ears, and paws between the toes.
Malassezia is diagnosed through microscopic examination of a skin scraping and treated with antifungal agents and medicated shampoos. Malassezia dermatitis is often mistaken for pyoderma. If your pug has been treated with antibiotics for a supposed case of pyoderma and still has problems, he may have malassezia instead.