Yeast Dermatitis

Laurie Anne Walden, DVM

Photomicrograph of Gram-stained Malassezia pachydermatis organisms. CDC/Janice Haney Carr.

Yeast skin infection (dermatitis) is common in dogs and also affects cats. Animals with allergies to pollen, grass, and other substances are especially prone to yeast dermatitis and yeast ear infections, so watch for the signs of infection if your pet gets itchy when the seasons change.
 
Causes
Yeast dermatitis is caused by Malassezia organisms on the skin. Malassezia yeasts are part of the normal collection of microorganisms that live on the skin and in the ears of animals. Yeast dermatitis occurs when something about the host animal—skin condition or immune function—causes Malassezia to overgrow or results in an abnormal immune response to Malassezia organisms. Examples of skin conditions that lead to yeast overgrowth are inflammation and increased moisture. Some animals are allergic to Malassezia and develop yeast dermatitis even when the number of organisms on the skin is relatively low.
 
These are some of the things that increase the risk of yeast dermatitis:

• Skin folds (yeast grow best in warm, dark, moist areas)
• Breed: West Highland white terriers, basset hounds, shih tzus, cocker spaniels, English setters, boxers, dachshunds, poodles, Australian silky terriers, Devon rex cats, sphynx cats, and breeds with deep skin folds[1]
• Allergic skin disease, such as allergies to environmental substances or foods
• Hypothyroidism, hyperadrenocorticism, and other diseases that affect the production of skin oils

 
Signs
The most commonly affected areas are the face, neck, armpits, belly, inner thighs, feet, and ears, although yeast dermatitis can affect any part of the skin. Yeast dermatitis typically causes these signs:

• Itching
• Redness
• Odor
• Greasy skin
• Crusty skin
• Thickened skin with a dark color (with long-term yeast dermatitis)
• Hair loss
• Reddish-brown staining around the base of toenails

 
Diagnosis
Samples from affected areas are taken with various methods (tape pressed to the skin, a microscope slide pressed to the skin, cotton swabs, scraping with a blade, or possibly skin biopsy) and examined under a microscope. Animals with yeast dermatitis might have very few Malassezia organisms visible with a microscope. In animals with long-term or recurring yeast dermatitis, other tests are often done to look for an underlying cause.
 
Treatment
Yeast dermatitis is treated with topical medication, oral medication, or both. Topical antifungal products include shampoos, mousses, wipes, creams, and so forth. Topical products need enough skin contact time to be effective, so shampoos usually come with instructions not to rinse the lather off for at least 10 minutes. A number of prescription oral antifungal medications are also used.
 
The choice of treatment type—topical, oral, or both—depends on the individual animal, the part of the body affected, the response to earlier treatment, and the ability of the animal’s owner to apply topical treatments. Not everyone has a place to bathe a large shaggy dog twice a week, for instance. Treatment for yeast dermatitis typically needs to continue for weeks.
 
For animals with recurring yeast dermatitis, the underlying cause also needs to be treated.
 
Reference
1. Bond R, Morris DO, Guillot J, et al. Biology, diagnosis and treatment of Malassezia dermatitis in dogs and cats clinical consensus guidelines of the World Association for Veterinary Dermatology. Vet Dermatol. 2020;31(1):28-74. doi:10.1111/vde.12809
https://onlinelibrary.wiley.com/doi/10.1111/vde.12809
 
Public domain image source: CDC/Janice Haney Carr

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