Since it seems this is only occurring in his hair, I would definitely stop using the Axe products. They may smell nice, but they aren't helping, so ditch those. Selsun Blue is a tar based shampoo which can be effective for things like dandruff, eczema, and psoriasis. Those are scaly type things. That type of shampoo could perhaps be aggravating the condition.
Our heads produce oils and it could be that his hair follicles are getting clogged. If you use anything too harsh, it could make his head produce more oils to compensate. It's the same with skin on your face.
You can try asking a pharmacist. You'd be surprised how many things they know about and can recommend.
In the meantime, I would recommend a witch hazel rinse. Witch hazel works wonders for many skin conditions. It's cheap, you can get it almost anywhere, it's not harsh, and is a wonderful astringent. It doesn't burn or sting.
I had a friend whose daughter had terrible acne on her face. She had tried everything, including Proactive, and it didn't work. I bought her some witch hazel and cotton pads and her skin cleared up beautifully. She'd been bombarding her skin with too many different things. One simple thing made a huge difference.
Again, run it by a pharmacist. It can't hurt.
Best wishes.