50 years old, seems like I've tried almost everything including prescriptions. Best advice I ever got was to stay away from Laurel Sulfate, an ingredient used to make products lather. I found soap like Yardley soap and shampoo by Cibu and recently discovered Buffy Body Butter by Lush.com I think the main ingredient is coconut oil. It has made my icthyosis and keratosis pilaris almost unnoticeable.
I also found it gets better with age, swimming in chlorinated pools, suntan and bleach baths.
I highly recommend trying the Buffy body butters. They are all natural.