In a large number of dogs, the mites cause no problem, but in some individuals, skin disease does result. Two theories 1 exist about why certain dogs develop demodectic mange, both of which deal with suppression of the immune system. While not proven to be inherited, most researchers believe the tendency to develop demodectic mange is hereditary, and most breeders seem to find evidence of certain families that are more prone to the problem. The second theory holds that it is not the mites, but a tendency to develop a bacterial infection along with the mange, which results in the bacteria suppressing the immune system. Either way, the result is the same, the mites and bacteria proliferate on the skin, causing hair loss, redness, etc.
Demodectic mange is seen primarily in two forms, juvenile and adult.
Juvenile mange is further subdivided into localized and generalized mange. The age at the onset of symptoms determines the diagnosis, with mange beginning before about 15 months of age considered juvenile. Localized juvenile mange is a common problem resulting in patches of hair loss, primarily involving the face and front legs, but which may be found anywhere on the body. The remaining dogs progress on to have generalized mange, which is characterized by more than 10 areas of hair loss, itching, bacterial infection and redness. Adult onset mange is that which begins in dogs more than about two years of age, and is not considered hereditary.