Malassezia are yeasts that live on healthy dog skin in small numbers. A 2020 review describes them as important skin commensals (normal residents) and opportunistic skin pathogens [5]. When something changes the skin, they can overgrow and cause Malassezia dermatitis, a yeast skin infection.
A yeast skin infection is usually not the whole story. Skin disease is favored by skin folds, underlying hypersensitivity (allergic) disorders, hormone diseases and defects of cornification (the way skin cells mature and shed) [5]. Your vet treats the yeast and also looks for the cause behind it [1].
Yeast also plays a part in several problems covered in other posts on this site; they are linked below.
Yeast on healthy skin
- A 1996 study of 19 clinically normal dogs found Malassezia organisms in low numbers as part of the normal skin microflora. Numbers differed by body site, with the highest on the chin [6].
- The University of Minnesota dermatology handbook notes that these yeasts are also found in normal ear canals and on other body surfaces of healthy dogs and cats. Their role as a disease cause on their own, without an underlying problem, is not clear [1].
- In scaling and greasy skin disorders, changes to the skin surface and its outer barrier layer often let yeast and bacteria overgrow [2].
Common underlying causes
The handbook and the reviews name these as conditions behind yeast overgrowth [1][5]:
- Allergies: atopic dermatitis (environmental or food related), food allergy and contact dermatitis are on the handbook’s list. A yeast overgrowth often makes the itch of an allergic dog worse [1]. See seasonal allergies in dogs and why is my dog so itchy?.
- Seborrhea (greasy or flaky skin): yeast and bacterial overgrowth are common complications of scaling disorders, and most of all of the greasy form [2]. See dandruff and dry, flaky skin in dogs.
- Hormone diseases: the handbook lists endocrine (hormone) disorders among the common predisposing causes [1].
- Parasites: skin parasites are on the same list [1].
- Skin folds: the 2020 review lists folds among the factors that favor the disease [5]. See pyoderma in dogs.
In some dogs no underlying disease is found [1].
What you may notice
The 2020 review describes itchy, red skin lesions, often with brown or black greasy material matting the hairs and a bad smell, that develop mostly in skin folds and areas where skin rubs on skin [5]. The handbook adds [1]:
- Itching varies from dog to dog but is usually severe.
- Some dogs have oily skin and coat, reddened skin and yellowish scales stuck to it. Greasy skin can carry a rancid smell [2].
- The paws are a common site. Redness between the toes and a rusty brown staining of the hair are typical, these dogs are often very itchy, and long-standing cases can show dark staining of the nails. See paw problems in dogs.
- Lip folds, armpits, groin and the skin around the vulva can turn red, sometimes with brownish staining of the hair.
- In long-standing cases, the skin becomes thick and dark. See dark, thickened skin patches on dogs.
- Ears: Malassezia is one of the organisms involved in outer ear infections, which are very common in dogs with atopic dermatitis [3]. See ear infections in dogs.
A smell is only a sign. It does not tell you whether yeast, bacteria or something else is the cause, so have your vet check the skin.
How it is diagnosed
- A skin sample under the microscope: the handbook calls cytology the most useful and readily available test [1]. The vet presses clear tape on the skin, or for oily skin may use a dry scraping, a swab or a glass slide, then stains the sample and looks for budding yeast under the microscope [1]. The 2020 review adds that diagnosis rests on finding the yeast in matching skin lesions and on seeing the skin and the yeast numbers improve with treatment [5].
- Yeast numbers need context: because yeast also lives on healthy skin, the 1996 study advised that the body site and sampling method be considered when making the diagnosis [6].
- Other tests: a culture is rarely needed, and a skin biopsy is kept for dogs whose signs are unusual [1].
- Looking for the underlying cause: with scaling skin, the main task is to work out whether the signs come from another skin disease or from a primary skin-cell defect; most cases seen in practice turn out to be secondary [2]. Your vet will choose further tests for your dog.
Treatment
Treatment is chosen by your vet. It has two parts: treating the yeast, and finding and managing the cause.
- Treatment on the skin: the handbook says skin treatment with degreasing and/or antifungal shampoos usually works, and other topical products may be used between baths or on small areas [1]. Use only the products your vet recommends, as directed.
- Treatment by mouth: antifungal medicine by mouth, combined with skin treatment, may be needed when the infection is widespread or does not clear with skin treatment alone [1][5]. Your vet will choose the medicine and how long to use it, and will recheck your dog before stopping [1].
- The underlying cause: the handbook stresses that finding and treating an underlying disease is key to managing the infection and preventing it from coming back [1]. The 2020 review likewise links managing other diseases with fewer relapses [5].
Outlook
- The 2020 veterinary consensus guidelines describe Malassezia dermatitis as a routine diagnosis today. In the authors’ view, several skin and oral treatments work, and they work best when the factors that set the dog up for it are found and corrected [4].
- When scaling skin is secondary to another disease that is found and controlled, the handbook gives an excellent outlook for the skin; a primary skin-cell defect usually needs lifelong care [2].
These are statements about groups of dogs. They do not prove that a treatment caused an outcome, and they cannot predict how one dog will do. Your vet can explain what the test results mean for your dog and whether an underlying cause needs long-term care.
When to see your vet
See your vet if your dog has:
- itchy, red skin, especially in skin folds or where skin rubs on skin [5]
- greasy skin, scaling or brown-black greasy material matting the hair [1][5]
- an unusual skin smell together with itching, scaling or hair loss [2]
- frequent licking or chewing of the feet, or rusty staining between the toes [1]
- skin that is darkening or thickening [1]
- skin problems that keep coming back after treatment [1][5]
FAQ
Is yeast on my dog’s skin always a problem?
No. Malassezia live on healthy dog skin in low numbers [6]. Problems start when they overgrow on skin that something else has already changed [1][5].
Why does it keep coming back?
Both the handbook and the 2020 review tie relapses to underlying disease [1][5]. If the underlying allergy, hormone disease or skin problem is not found and managed, yeast can overgrow again.
Can my vet tell from the smell?
No. A smell is only a sign. Diagnosis is usually made by looking at a skin sample under the microscope [1][5].
Do I need a special shampoo?
Ask your vet. Medicated shampoos are a usual part of skin treatment [1]; your vet will pick the right one for your dog.
The bottom line
Malassezia yeasts are normal residents of dog skin that can overgrow when skin folds, allergies, hormone diseases or skin cell problems change the skin [1][5][6]. Diagnosis is usually made by cytology [1], and treatment pairs antifungal treatment with finding and managing the underlying cause [1][5]. If your dog’s skin is itchy, red or greasy, see your vet.
This article is for general information and does not replace a visit to your veterinarian. If your dog’s skin is itchy, greasy or smells unusual, contact your vet.
Sources
- Torres SMF. 4.3 Malassezia Dermatitis: Small Animals. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology/chapter/malassezia-dermatitis-small-animals/
- Torres SMF. 3.1 Disorders of Keratinization: Learning Objectives, General Consideration and Classification. Small and Large Animal Dermatology Handbook, Vol. 2. University of Minnesota, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology2/chapter/disorders-of-keratinization-canine/
- Torres SMF. 2.10 Otitis Externa: Dogs and Cats. Small and Large Animal Dermatology Handbook, Vol. 1. University of Minnesota, 2025. CC BY 4.0. https://open.lib.umn.edu/animaldermatology/chapter/otitis-externa-dogs-and-cats/
- 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. https://pubmed.ncbi.nlm.nih.gov/31957204/
- Guillot J, Bond R. Malassezia Yeasts in Veterinary Dermatology: An Updated Overview. Front Cell Infect Microbiol. 2020;10:79. CC BY 4.0. https://pubmed.ncbi.nlm.nih.gov/32181160/
- Kennis RA, Rosser EJ Jr, Olivier NB, Walker RW. Quantity and distribution of Malassezia organisms on the skin of clinically normal dogs. J Am Vet Med Assoc. 1996;208(7):1048-1051. https://pubmed.ncbi.nlm.nih.gov/8621316/