Dog yeast infection is caused by an organism found normally on the pet's skin called Malesezzia. This can overspread into the your dog body if it has the proper conditions. The fungus thrive in dark, moist areas. So, this is the reason most og with long ears and long hair can develop easily canine candida. Another factor is a weak immune system. Older dogs can get easier yeast infections compared to the youger ones. Antibiotics and steroids are big factor also.