[Drago]

A picture, even if it's blurry would really be helpful! Do you have a sandbath in your cage? Hamsters, quite like humans, can get dry skin for a variety of different reasons. However if you mention that it is like psoriasis, I wouldn't think dry skin to be the most likely cause. To me, it sounds like it's possible it could be an ammonia burn. These are often raised, red, swollen, crusty yellow patches on hamsters which are caused by irritation to the skin from ammonia. Overall pictures would really help us to determine more! Hope all is well with him