my mouse is losing its hair

[pepsi111]

ok this is what has happened

i have just breed my first bunch of baby mice and then i feed all but one to my reptiles this one i had to keep because my girlfriend got anoyed that i was killing little mice and yea this one is slowly losing its hair. it has lost all of the hair off his head and starting to go down his back...

so pretty much im wondering if hes pulling it out or if his mum is or is he has a disease??

i am happy to answer and questions you would like to know...