Wow!! Okay I have scalp psoriasis but am much older than your son. Mine is plaque posoriasis which looks as though, even on body/scalp that you can peel it off. There is not cure for psoriasis but some shampoo's can help some. Forget the head and shoulders if thats what it is because it only masks' the problem. I found using a lilac shampoo and rinsing with vinegar helped some. Other times I use the lilac and "sweet grass" shampoo. You don't want anything harsh. My Physician gave me a lotion for my hair to keep the itch away. I believe it is called Betamethasone. If you scrub hard and you put this on, even vinegar (mix half water half vinegar) because you sure feel a burning sensation). I expect it but your still never prepared, so I don't know that your son would like it "period". I also have cream that I use for other patches around my body. I have checked everywhere for solutions, I even had some company on the internet call me after writing, asking for $600.00 to send to Africa. I think not. I didn't even know if this place was real. I've been to Dermatologists, going again this month. I even have it in my nails which I didn't know until last yr via Dermatologist. This is where your Dr. my send you, especially if your son is complaining of itch.
Believe me its not fun and ppl. look at your hair like you have something contagious. I've had ppl. say to me "whats in your hair" or do you have "psoriasis". I'm glad some ppl. know what it is. At times I could just crawl under the table. Get the help for him now if you can, they say stress and the immune system is the problem. I don't know. I would hate for your son to get it worse as he gets older and others begin to see it, if not controlled. Nothing worse than being made fun of especially around girls when they are at that age. Good luck and make sure he gives you something to at least assist the itching. If nothing else for the scalp, use the vinegar. Another one is, and he won't like this. Put baby lotion in his hair, let it soak in for about an hr. Then wash out, it may take about 3 washes but the flakes should come right out. All my best to you and your son and Good Luck with your Physician. My apologies for the not so good experiences'. I didnt get this until I was maybe 49, so have been putting up with it for 4yrs. now.