S.C.
My son had terrible cradle cap and at 7 months old was diagnosed with food allergies - milk, eggs, and peanuts. He also had the same symptoms: rough patches, dry skin, little rashes everywhere. Everyone told me to use special shampoos, lotions, soaps, etc.... when it was really the food. We ended up with an ambulance ride and a night at Children's Hospital over a drink of milk.
You may want to have him tested; it's best to know at a young age. They can do a scratch test at any age. Good luck!