Demodex mites are actually a normal inhabitant of your dog’s skin. These mites live in the hair follicles of dogs and are passed from the mother to her pups during nursing. The dog’s immune system normally controls the number of mites, so that they cause no harm. Dogs can develop signs of disease if their immune system is unable to control the mite population. This most commonly occurs in young or malnourished dogs, or those with other diseases that compromise their immune system. Signs of disease due to Demodex mites include hair loss, thickening of the skin, and skin infections. Cats have their own species of Demodex, however signs of disease are much less common in cats compared to dogs.