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.
The dark footprint-like structures seen here are the yeast organisms Malassezia pachydermatis. Photo by CDC
Why Suspect Yeast?
Yeast infections are itchy, crusty, and smelly. Often a dog starts out with a rash or with 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. Mostly dogs are affected but cats can get yeast infections as well.
Where Would a Dog Get a Yeast Infection?
Yeast happily live 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 actually become allergic to the proteins in the yeast cell wall (see below) so that very few yeast organisms are needed to incite very big inflammation.
So what conditions lead to a yeast proliferation? An increase in skin oils (which often occurs in an allergic flare up) would be the most common situation. Sometimes there is an immune deficiency that allows the yeast proliferation. Some animals are battling seborrhea (excessive oil production of the skin) and thus are naturally predisposed to the yeast proliferation. Some animals are actually 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.
Note the elephant skin appearance that is especially common with Malassezia dermatitis. The more scientific term for this finding is lichenification. Photo by Carol Foil DVM
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.
How is Yeast Infection/Overgrowth Confirmed?
There are several testing methods to confirm the overgrowth of yeasts:
- Impression smear (pressing a microscope slide on the skin to collect yeast organisms)
- Scotch tape sampling (pressing a piece of clear tape to the skin to collect yeast organisms)
- Skin scraping with a blade (scraping the skin with a blade to collect yeast organisms)
- Cotton swab (rubbing a moistened cotton swab on the skin to collect yeast organisms)
- Skin biopsy (removing a small plug of skin with a biopsy punch with a local anesthetic. This is the most invasive choice but provides substantially more diagnostic information.)
Very few yeasts need to be seen under the microscope to confirm yeast infection.
How do we Get Rid of it?
This dog's skin also shows lichenification
along with redness from active inflammation. Photo by MarVistaVet
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 added.
There numerous medicated shampoos available for veterinary patients at any given time and new products are constantly being developed. Because there are so many products coming and going, we will limit our discussion to active ingredients rather than brand names.
While degreasing shampoos such as the benzoyl peroxide and sulfur/salicylate shampoos will help remove the skin oils feeding the yeast, there are shampoos that are specifically anti-yeast. We prefer the four percent chlorhexidine shampoos or Malaseb® shampoo as these both strip skin oil and kill yeast; however, other anti-yeast products include those containing selenium, vinegar, miconazole, ketoconazole and more. The pet must be bathed twice a week to start and the shampoo requires a 10-minute contact time (meaning do not rinse the lather for 10 minutes).
If only a small area is involved, it is probably not necessary to bathe the entire animal. Acetic acid wipes can be used to cleanse the affected area. Mixtures of vinegar and water can be used, but the pet will develop a distinct vinegar odor.
Treating the Underlying Cause
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 not controlled, yeast dermatitis is likely to periodically recur. It is common for allergic dogs to require some kind of periodic if not on-going anti-yeast therapy.
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