Hello Minnie90, I'd be glad to help you with your sons' problem with Psoriasis condition. I can imagine how frustrating that must be for the both of you.
Without going into much detail about it, external treatments for this condition are very minor helpful at best. I would suggest that you look online for "The Wheatgrass People", their company is located in KS. and get him a bottle of wheatgrass tablets. The protocol is to give him 10 small tablets 3 times a day for 6 weeks.
*The end results after this 6 wk. protocol is he will have no sign whatsoever of the Psoriasis condition.
*You would need to purchase 3 of the 500 ct. bottles would be plenty. Good health to you and your son! God bless!