They are simply a nuisance for a pet. These mites dig holes in the skin and lay eggs. Dog's skin becomes itchy causing them to scratch their skins. Some times dogs scratch so much that it causes wounds and start bleeding. Bathing dogs with good dog soap is one option. There are sprays which can be used to kill mites hidden in the skin and they can be used without bathing the puppy. In extream cases, vet's treatment is important.