And it could be something simple...how old is he? If he is small like your avatar photo then he could be at the age where Yorkies 'blow their coat'. Which means he is in transition from his puppy coat to his adult coat...their skin gets dry and looks dull and they will lose some hair. Is he shedding too? This stage usually hits between 6 and 10 months of age if I remember correctly.
Good luck...I hope that's all this is
