Yeast Infection In Dogs – Causes and Treatment

Written by Vet Evidence Based

Yeast infections are quite a common skin condition that occurs in canines. Although yeast always inhibits our dogs' skin, ears and mouth, excessive growth of it can lead to health issues that need adequate care and treatment. In this article, we're telling you more about yeast infections in dogs and the ways they should be treated.

dog licking skin

Yeast infections in dogs are actually quite a common problem and often cause sore ears or skin disease. These infections are also known as yeast dermatitis or Malassezia dermatitis. Dermatitis just means inflammation of the skin.

This may come as a surprise but yeast normally live on the skin of dogs in small numbers, but they can cause disease and inflammation when they abnormally multiply on the skin. So, a few yeast are ok but when there are lots, the skin cannot cope!

In this article, we will take a closer look at this common skin disease of dogs. We will discuss the signs of a yeast infection and how it is diagnosed and treated. First, let’s find out what exactly is yeast? And you might have already heard other people or your veterinarian mention it before, but what is Malassezia?

What Exactly is Yeast?

Yeast is actually a single-celled organism and fungus. Most people might just recognize yeast as something used in baking and for brewing alcohol. However, there are many different types of yeast, and the one used in baking is different from the one that lives on your dog’s skin.

Yeasts are found on the surface of the skin and also in the intestinal tract of all mammals, like us humans and our dogs(1). If it grows out of control, it will cause a yeast infection, which is more common if your dog has a weak immune system or has other diseases too.

The most common species of yeast found on the skin of dogs is called Malassezia pachydermatis(2). This lives in small numbers on the surface layers of the skin, in the ear canals and on the mucosal surfaces (mouth, anus, and vagina) of healthy dogs. For the majority of dogs, this yeast causes no harm, but when the numbers start to increase it causes Malassezia dermatitis. Later in the article, we will discover why the numbers of yeast might increase, and what dogs are prone to yeast infections. First, let’s take a look at the signs your dog might show if he is suffering from a yeast infection.

Signs of Yeast Dermatitis

Skin lesions may be localized to one area of the body or just the ears, but in severe cases, the entire body might be affected. The skin is usually extremely itchy and has an unpleasant characteristic “yeasty smell”. If a dog has a chronic case of yeast dermatitis, the skin might start to change and becomes thicker and slightly darker in color too.

Common clinical signs of yeast dermatitis include:

  • Itchy and red skin (face, neck, armpits, groin, legs, and paws)
  • Itchy and red ears
  • Red, moist, skin folds
  • A strong, musty odor
  • Scaly, crusty skin
  • Hair loss
  • Thickened skin (also known as elephant skin)
  • Changes to the pigmentation of the skin
  • Chronic or recurrent ear infections

Why Does Yeast Only Sometimes Cause Disease?

Like we mentioned before it is normal for dogs to have small numbers of Malassezia yeast on their skin and in their ear canals. A dog’s immune system keeps the numbers under control and prevents the yeast from multiplying. So, what allows the yeast to increase in numbers and sometimes cause a yeast dermatitis?

Common reasons for yeast numbers to increase on the skin and cause yeast dermatitis include(3, 4):

  • Humid Climates
  • The dog suffers from an allergic skin disease
  • The dog has excess oils on the skin e.g. seborrhea
  • The dog is receiving immunosuppressant drugs such as corticosteroids
  • The dog has a weak immune system
  • The dog has a hormonal imbalance e.g. Hypothyroidism or Cushing’s disease.

Therefore, if the conditions on the skin change due to another disease or infection, or of the immune system is not working as normal, then the yeast numbers can increase and cause a yeast infection.

Are Certain Breeds More at Risk of a Yeast Infection?

Yes, some breeds seem more predisposed to developing yeast infections. Therefore, genetics is also thought to play a role in the development of yeast dermatitis. Several breeds more commonly develop yeast dermatitis than others, including West Highland white terrier, Basset hound, American cocker spaniel, Shih Tzu, Poodle, Boxer and Cavalier King Charles spaniel(5).

Now, we know why some dogs develop yeast infections and that some breeds are more prone to developing it. However, now let’s take a look at how to diagnose yeast dermatitis.

How is Yeast Dermatitis Diagnosed?

Yeast dermatitis may be suspected from the clinical signs of the dog, and the appearance and smell of the skin. However, there are a few different techniques which veterinarians use to collect samples in order to diagnose yeast dermatitis:

  • 1. Skin scrape – The top layer of the skin is scraped with a bade to collect the cells, then transferred to a microscope slide.
  • 2. Impression smear – A microscope slide is pressed onto the skin to collect yeast organisms.
  • 3. Swab sample – A cotton swab is rolled on the skin to collect yeast organisms.
  • 4. Acetate tape – A piece of clear tape is pressed onto the skin to collect cells.
  • 5. Skin biopsy – A small piece of skin is removed either surgically or using a biopsy bunch. This is the most invasive technique but also provides the most information.

Once the sample from the skin is obtained using one of the above methods, it is viewed under a microscope to check for yeast.

Treatment of Yeast Dermatitis

If a yeast infection is confirmed from the laboratory tests, then a treatment plan will need to be planned. The treatment depends on the number of yeast present and if the dog has any other underlying medical conditions (allergies, bacterial infections, hormonal imbalances etc.). Treatment plans for yeast dermatitis may be topical or oral, or sometimes a combination of both.

Topical Treatment

This involves using medicated shampoos, ointments, creams or ear drops to treat the yeast overgrowth. The chosen shampoo depends on the severity of the yeast infection and also the type of skin the dog has (oily, dry or flaky?). The antifungal shampoo contains anti-fungal ingredients such as miconazole, climbazole, ketoconazole or chlorhexidine(6). The affected areas are dampened and the shampoo is lathered onto the skin. Often the shampoo is left in contact with the skin for 10 minutes before it is fully rinsed. However, you should always follow the instructions on the shampoo leaflet or those given to you by your veterinarian. If the yeast infection only affects one or two small areas of skin a topical ointment may be prescribed instead. If the infection affects the ears (yeast otitis), then an ear drop solution will be prescribed.

Oral Treatment

In some cases, oral anti-fungal treatment will be required, especially in severe or chronic yeast infections. Often a dog with yeast dermatitis will also have allergic skin disease or a bacterial skin infection too, and these will require treatment at the same time. Chronic bacterial skin infections may need antibiotic tablets for 4-12 weeks to get rid of the infection! Common oral anti-fungal medications may be prescribed in tablet or liquid formulations and include ketoconazole, itraconazole, terbinafine or fluconazole(7, 8). Yeast dermatitis often needs to be treated for weeks or months. It is not a quick cure! Oral anti-fungal medication also has a number of potential side effects, meaning it may not be suitable for all dogs and dogs receiving this medication may need regular blood tests to monitor their liver.

Treatment (oral or topical) often needs to be continued for some weeks or even months before the yeast numbers return to a low normal level. The veterinarian will usually need to repeat a diagnostic skin test to check the levels of yeast before the treatment is stopped. If the treatment is stopped too soon, the yeast infection will quickly return, which can be very frustrating for both the owner and the dog too!

What is The Prognosis for Yeast Dermatitis?

The prognosis for a simple yeast dermatitis is normally good. However, often this dermatitis does require weeks or sometimes months of treatment, but the majority of dogs improve within the first week and can be completely cured.

However, treatment success depends on any other underlying conditions the dog has. It is important that any underlying trigger is identified and treated or else the yeast dermatitis will just keep coming back. This means diagnosing any allergies, bacterial infections, hormonal imbalances or immune system problems the dog has. Therefore, the prognosis of recurrent yeast infections depends on the control of any underlying problems. Your veterinarian should work with you to make a complete treatment plan to help control any underlying problems and manage the condition in the long term.

Conclusion

Yeast dermatitis is a common problem in dogs and is caused by the overgrowth of the yeast Malassezia on the skin. It is normal for yeast to be present in low numbers on all healthy dogs, and they only cause a problem when their numbers increase. Often this increase is due to something which changes the natural balance of the skin such as high humidity, bacterial skin infections, allergies, a weakened immune system or immunosuppressive drugs.

Treatment can consist of topical or oral medication, or sometimes a combination of both. There are some possible side effects associated with oral anti-fungal medications, which means it is not suitable for all dogs, especially those with a history of liver disease. It is really important to treat any underlying conditions which might be causing the yeast infection in the first place, or else the yeast dermatitis will just keep coming back. If you think your dog has a yeast infection it is important to seek veterinary help, so that your dog can keep yeast free and healthy!

This article has been written by Dr Margarita Boyd, BVSc MRCVS.

Margarita graduated from the University of Liverpool, earning a Bachelor in Veterinary Science with distinction. She worked in small animal and equine practice for a few years, before choosing to focus solely on companion animals. She has developed a special interest in internal medicine and ophthalmology.

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