Mouse with hair loss and dark skin

Hi everyone,
This is my first time using this forum. I have a mouse that is approximately 8 months old (according to the pet shop it was a baby when I got it). (I have 2 mice) She has done really well, and looks great, very alert and active, but I dont know why she is losing fur in a couple of places. Can anyone help? There are no sores, no greasy areas, it doesn't look itchy and it doesn't seem to bother her. She is a black and white coloured mouse, in splotches, and now the places she has lost hair, the skin underneath is going dark. I did think she may have lost some patches of hair because of rubbing it, but i just dont know.

Does anyone have any ideas about what's going on? As I said, she looks ok, is very alert and active, is eating and acting quite normally.

Thanks in advance for any feedback

Natcb

It's normal for the skin to go dark where the hair loss is, because the temperature of the skin is lower there.

Is it possible one of other mice may be pulling her fur out?

Or, mass inbreeding of the kind that is done with pet store mice could result in alopecia and there isn't much you can do about it except to make sure she's warm!

I decided to look online could be the mouse has mites or a fungal infection, you will need to have a vet check hime out

http://animal-world.com/encyclo/critters/mouse/mouse.php

http://www.rmca.org/