My baby has a thick layers of flakes on his skull. Is it because of the shampoo that has cause this problem?Currently I use kodomo bath and shampoo that is given in the hospital package. Should I change the shampoo to those not so harsh for baby?

Likely to be cause by cradle cap. You have to wash your baby's hair regularly with a baby shampoo, and then loosen the flakes using a soft brush. Rub a mild baby oil or olive oil oil into your baby's scalp. After that gentle wash away the cradle cap.