Skin Parasites, also known as mites can cause hair loss on a hamsters tail, lower back area, and legs. These spots may also itch. Your vet can give you medication.
Just like any other haired animal when it gets old, hair starts to fall in body areas that are always rubbed. On the other hand, infection could be a cause.
This can happen from frequent diarrhea. The constant irritation can end up making the hair fall out, causing the bald area of the fur. You should make sure the hamster stays hydrated.
Well,when i was a kid i had a hamster and i got a similar problem.I went with him at a doctor and he said that is a infection that he got from the food.