Why my hamsterhas a bald spot on the middle of its forehead?

Question
   I got a new hamsters in front of a market today. And one of them has a bald spot on it's forehead. The person who sold me the hamster told me that the hamster are one month old. Do you think it's a disease? And also I have another hamster do you think I should separate them immediately?  

Answer
Lilly,
from what you are describing it could be two things.  First of all I'm thinking mites.  Check the area that's missing the hair very carefully... usually the mites are visible.  If not that, then it might be that it was fighting with another hamster.  If you find mites, you can pick up a commercially available mite treatment. Yes I would separate it from the others until you figure out what it is.