Is your hamster old? Sometimes they just start loosing hair when they are older. My hamster has that same problem. She got mites because of bad circulation in her cage (problem is fixed now). You can buy stuff to spray in their cage or on them. If you spray it on them make sure you keep it out of their face and keep them very warm.
Hope your hamster is okay :) let me know!
Maddy :D
Hope your hamster is okay :) let me know!
Maddy :D