Knowledge of the ability of bacteria to cause skin/ear infections in animals has been well known for many years. Knowledge of the ability of yeast to cause disease in the skin/ears of animals has increased dramatically over the past 10 years. Candida (the cause of the disease “Thrush” or “Candidiasis” in humans) has been studied for years. Yeast from the genus Malassezia (previously Pityrosporum) are now recognized for the ability to cause problems in canine and feline ears and skin. Malassezia are also found in many other animals and are found humans, especially those humans with atopic eczema.
Malassezia are a type of yeast that can be found in the body, such as the lower intestinal tract and sometimes the nasal passages of dogs and cats. They normally do not cause problems in pets with healthy skin. However, when the health of a pet’s skin is reduced or weakened by allergies or by another health problem, the skin and ears become susceptible to the development of large colonies of yeast living in these areas. Yeasts are known to produce substances that cause irritation and inflammation and their presence, for most individuals, causes discomfort and even the development of true infections.
So, Malassezia “like” allergic skin and ears and their presence can stimulate the production of excessive discharge from the walls of the ear canals. A thick brown or black discharge is a hallmark of yeast infection, although other types of ear infections and also ear mites can result in a dark discharge.
Ears and skin with Malassezia overgrowth or infection often have an odor and some owners become adept at recognizing the yeasty smell. The odor is from abnormal composition of skin oils from inflamed skin and probably also waste products of the yeast.
The allergy connection:
It has been shown in people and in dogs that some individual’s skin actually becomes allergic to components or products of the yeast organisms. This adds insult to injury. Not only do yeast like allergic or inflamed skin, but in addition the allergic individual’s skin reacts adversely to the yeast resulting in further skin irritation and likely further yeast growth. Some of the most intensely pruritic, paw-chewing dogs seen are allergic individuals with yeast infections.
Can you get rid of yeast?
Unfortunately, one cannot sterilize the body – remember that yeast are present normally in every animal’s intestinal tract. The intestinal tract is an endless source of yeast for future skin or ear infections. What does help prevent yeast ear or skin infections from recurring is making the ears and skin less susceptible to yeast. As with bacterial skin infections, the most common reason for yeast ear/skin infections is allergic skin disease. Controlling allergies helps the ears and skin be healthy and a less suitable place for yeast to grow.
Systemic Drug Therapy:
Drug therapy is important in reducing yeast numbers on the skin or in the ears and along with controlling allergies usually helps the pet. Typically, antifungal medications are used – these are typically oral drugs designed and approved for use in humans and used off-label, unapproved for dogs. For canines with skin/ear yeast infections, these drugs are a big help. They are used in cats also, though cats may be more sensitive to side effects of these medications than dogs.
Topical antifungal therapy:
There are now many good veterinary products with antifungal ingredients that are effective against yeast. Useful active ingredients against yeast include chlorhexidine, ketoconazole, miconazole, clotrimazole, other “-azole” antifungal drugs, and boric acid. As with any topical therapy the amount of time the product is on the skin is key to effectiveness. So, if using a shampoo containing the active ingredient, it must be left to soak on the skin for an adequate time.
Regardless of the antifungal therapy – whether oral or topical, the infections will not dissipate for any length of time without improving skin health – typically controlling the pet’s allergies.
Does excessive antibiotic use cause yeast infections?
This may be the case in humans, such as individuals with severe infections requiring long courses of powerful antibiotics – some of whom end up with infections by Candida such as of the oral cavity (“Thrush”) or other areas of the body. Antibiotics alone, in my opinion, don’t typically result in Malassezia skin/ear infections in an otherwise healthy dog or cat. The exception though is the dog or cat who, because of allergy or some other skin disease, is already susceptible to yeast or bacterial skin/ear infections. Then, when an antibiotic is given, bacteria present in the unhealthy areas of skin or ear canal are decreased which improved conditions for the growth of yeast.