My teenager has small flaky scabs all over his scalp that itch sometimes. What could this be?

Psoriasis probably. It doesnt always look like the images on the internet.

Too much sugar in the diet tends to cause it. But one of the 5 common trigger foods might also be to blame. Try a steroid cream, if it gets better it’s probably something autoimmune. Changing his diet will fix it long term. If you live in the south or a tropical place with high humidity all the time there is also a fungus that can develop. (and cause hair loss) I bet tea tree oil would take care of that too but prescription antifungals do exist.