There are a several different underlying causes of hair loss in puppies. I am only going to address a few of them.
Patchy hair loss with associated pruritus (itchiness): The most common cause for patchy hair loss is fleas. However, it can also be caused by the Sarcoptes mites. This is often referred to as “Sarcoptic Mange.” Infestation with Sarcoptes mites causes severe pruritus. The puppies will scratch constantly. Because of the constant scratching, and the damage that it does, the puppies often develop a bacterial skin infection. These puppies will have red, crusty skin lesions in addition to the hair loss. Sarcoptes mites live on the skin, and treatment is usually topical. However, due to the skin infection, the puppies may also need to take antibiotics. Sarcoptes mites easily transfer to other pets and can cause itchiness in people as well. They don’t infest humans, meaning they don’t set up permanent residence on our skin. However, they will bite us if given the chance.
Patchy hair loss without pruritus: There are two common causes for these symptoms in puppies. The first is ringworm (See #13 Ringworm for details). The second common cause is another mite called Demodex, often referred to as “Demodectic Mange.” These mites live in the skin. They do not typically cause pruritus, so the puppies don’t usually scratch. The treatment for demodectic mange is oral and usually requires a long treatment therapy.
Demodectic mange is not contagious to other pets or people. The puppies actually obtain the mite from their mother, during nursing. In addition, there is a genetic component that determines whether or not the animal will have any symptoms associated with the infestation.
In conclusion, several underlying factors cause puppy hair loss. Therefore, it is important to consult your veterinarian for a specific diagnosis and treatment options.