First of all I'd rinse the hamster a few times to make sure the soap residue was off of him.
He might be actually have a kidney problem or he could have picked up ringworm (a fungus) if many children handle him.
This site has excellent info on hamster health and care
http://www.hamsterific.com/IllnessGuide.cfm
see if anything in their above illness guide matches what you are seeing.
You might try plain aloe vera on some of the skin to see if that helps moisturize it.
But if this is ringworm or mites you will need help from the vet to resolve this.
Hope this helps you!
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