Today’s VETgirl online veterinary continuing education blog is on yeast dermatitis in dogs and cats. Thanks to guest blogger, Dr. Nicole A. Heinrich DVM DACVD, at McKeever Dermatology Clinics for this veterinary dermatology help!

Many types of yeast exist in the world. Yeast to make bread dough rise is called Saccharomyces. The yeast that commonly affects humans is called Candida, and the yeast that affects dogs and cats is called Malassezia. While they are all yeast, they do not all behave in the same way.

Malassezia is a type of yeast that is naturally present in low numbers on the skin and in the ears of dogs and cats. If the skin and ears are normal, and if the immune system is normal, the yeast numbers remain low. The low numbers of yeast combine with low numbers of bacteria to form the normal flora of the skin and ears. Normal flora protects the skin and ears so that bacteria from the environment does not colonize and infect the body. However, if the skin and/or immune system is not normal, then Malassezia can overgrow and cause a yeast infection.

In dogs, yeast can overgrow anywhere on the body, but the most common areas are the following:

  • ears
  • paws (particularly between the pads and in the claw folds)
  • axillae
  • ventral neck and the
  • perivulvar region.

In cats, yeast most commonly overgrows in the ears and on the paws. While these are the areas that are most commonly affected, a yeast infection can occur on any part of the skin.

The most common signs of a yeast infection are:

  • dark brown to black waxy debris in the ears
  • brown discoloration of the hair
  • accumulation of brown waxy debris in the claw folds
  • brown discoloration of the claws
  • erythema of the skin
  • pruritis

More importantly, yeast is very itchy. The pruritus caused by a yeast infection does not respond to treatment with allergy medications. The only way to resolve the pruritus caused by a yeast infection is to treat the infection directly.

While the clinical signs can give the clinician a high index of suspicion that the patient has a yeast infection, the only way to diagnose the infection with certainty is with cytology. The reason that it is important to perform cytology (tape preparations and ear swabs) to confirm the diagnosis is that some bacterial infections will mimic a yeast infection.

Malassezia observed through a microscope

Many treatments for yeast infections are available. When choosing a treatment, the clinician must first consider if the patient has any contraindications for a certain treatment such as: co-morbidities, sensitive stomach, receptiveness to topical therapy and other medications that may lead to drug interactions.

The following is a list of common treatments for yeast infections:

This list is a quick reference guide only, and a pharmacology textbook should be consulted for complete information. The list is not exhaustive. Topical therapies and systemic therapies sometimes need to be prescribed in combination.

Once the yeast infection has been resolved, proactive steps must be taken to prevent the yeast infection from returning. This may involve regular (e.g., weekly) topical therapy with an anti-yeast product. More importantly; however, the underlying cause of the yeast infection must be determined. Don’t forget to rule out common causes of yeast infections including:

atopic dermatitis, food allergy, hyperadrenocorticism and hypothyroidism. Resolving and preventing yeast infections often makes it easier to manage these other problems.