Malassezia Dermatitis (Yeast Infection of Dog's Skin)


One of the most enjoyable parts of practicing veterinary medicine at the Manchester Animal Hospital is seeking a diagnosis in a case with multiple rule-outs.  One example was a patient with crusty lesions on the tip of its ears.  Because there are multiple possible causes for this, experience is helpful, but only certain diagnostic tools should be employed.  In this case, I suspected a fungal/yeast diagnosis, bacterial dermatitis, or skin mites, also known as mange.

There are several testing methods to confirm the overgrowth of yeasts and rule out other causes, such as Demodectic and Sarcoptic Mites.

  • Skin scraping with a blade (scraping the skin with a blade to collect yeast organisms) is a test that can help rule out mites as a cause. The skin scarping is then studied under a microscope and, in this case, provided the diagnosis that ruled out other causes.
  • Skin biopsy (removing a small skin plug with a biopsy punch with a local anesthetic.  This is the most invasive choice but provides substantially more diagnostic information.)
  • It is important to realize that yeast overgrowth occurs in response to a primary problem, be it allergy, seborrhea, or something else.  If the underlying problem is uncontrolled, yeast dermatitis will likely recur periodically.  It is common for allergic dogs to require some periodic if not ongoing, anti-yeast therapy.

Therefore, I also tested for food and airborne allergies in this case.  The following results provided a plan: The food and airborne allergies defined what foods the dog should not eat, and the other allergy tests were also positive, giving a direction to treat also.

The skin scraping tests provided a cytology sample (examining cells under a microscope) that proved that it was a Malassezia infection.

Yeasts are the spore-like forms of fungi; Malassezia dermatitis is the inflammatory skin disease that results from overgrowth on the skin by the natural Malassezia yeast population.

Yeast infections are itchy, crusty, and smelly.  Often, a dog starts with a rash or simple itching, but the skin thickens to an elephant skin appearance.  The itch is extreme, and the odor can be especially troublesome.  Parts of the body or the entire body can be affected.  Dogs are mostly affected, but cats can also get yeast infections.

Yeast happily lives on most normal skin and in ears and anal glands.  To get a yeast infection, conditions on the skin surface have to change to favor the proliferation of the yeasts.  The yeasts in small normal numbers are harmless, but when the yeasts are in large numbers, disease results.  It is also possible to become allergic to the proteins in the yeast cell wall (see below), so very few yeast organisms are needed to incite very big inflammation.

So, what conditions lead to yeast proliferation?  Increasing skin oils (often in an allergic flare-up) would be the most common.  Sometimes, there is an immune deficiency that allows yeast proliferation.  Some animals are battling seborrhea (excessive oil production of the skin) and thus are naturally predisposed to yeast proliferation.  Some animals are allergic to the yeasts themselves.  The most important thing to realize is that while a yeast infection is not contagious, it tends to recur unless the underlying allergy, seborrhea, or other problem is controlled.

The following breeds are predisposed genetically to yeast infections: the West Highland White Terrier, Basset hound, Cocker spaniel, Silky terrier, Australian terrier, Maltese, Chihuahua, Poodle, Shetland sheepdog, Lhasa apso, and the Dachshund.

Very few yeasts need to be seen under the microscope to confirm yeast infection.

Treatment can be topical, oral, or both.  Topical treatment is best used for localized spots of infection, while oral medication would be better applied to larger infected areas.  If the yeast infection is recurrent or if you wish to supplement oral medication, topical and oral treatment can be combined.

Ketoconazole and its derivatives rule when it comes to oral therapy.  Typically, a several-week treatment is needed, and there are numerous protocols involving different dosing schedules. Higher doses tend to be needed if recurrence is a problem.  The extreme itch usually improves or resolves within one week.  For animals that do not tolerate the azole class of medications, terbinafine is a good alternative choice. 

If oral medications are not effective, this suggests a biofilm has formed, and topical treatment must be considered. in this, a topical medication with Ketoconazole was Rx’d.

Recently a consensus statement was published by veterinary dermatologists regarding Malassezia dermatitis.  When it came to shampoos, those favored contained 2% miconazole and 2% chlorhexidine.  Shampoos were applied twice weekly with a ten-minute contact time before rinsing.  

This type of therapy helped improve the effectiveness of the oral medication and was also a good choice for long-term maintenance therapy once the infection was controlled.  There are many shampoo products available with these active ingredients, such as vinegar bases, selenium, and/or topical ketoconazole.  Your veterinarian may have a preferred product or regimen.

It is important to realize that yeast overgrowth occurs in response to a primary problem: allergy, seborrhea, or something else.  If the underlying problem is uncontrolled, yeast dermatitis will likely recur periodically.  It is common for allergic dogs to require some kind of periodic if not ongoing, anti-yeast therapy.

Dr. Lamb is the Veterinarian at the Manchester Animal Hospital.