What is the mange, is there different types of mange, how does a dog/puppy get the mange and how can I treat?

My 12 month old american pit bull terrier has been treated for mange and mites about 3 months ago. She is showing signs of having it again because she is scratching a lot and missing hair in the spots she is itching the most. I have been told by fellow pit owner that there are two types of mange. One of them being hereditary and can be brought back due to stress and other things. Is this true and if it is will she have it all her life?