Hi Amir
Some pigment spots on a male hamster can be normal, if there is a matching spot each side of his rear there's much less for you to worry about. If he's active, eating and drinking that's also great but If the hair loss continues that might be a problem. The only way for you to know for sure if he's healthy is to get him checked at a vet.
Cathy Wickenden BVet Med MRCVS
Barton Lodge Veterinary Centre
1 Midland Road, Hemel Hempstead, Hertfordshire, HP2 5BH
Tel: 01442 216048 24 hours
[
www.bartonlodgevets.co.uk]