I realise this is a older thread, but I wanted to add something natural that I found makes a massive difference to my KP arms - coconut oil! I think it's a mixture of the moisturising and anti bacterial qualities it has. You have to go easy or you look like a grease slick though!! I often use it before end or when it's bad in the day. You have to be careful in the sun though as it acts the same way as oil on your skin - enhancing the burn!!!!
I've had it all my life and my daughter does too. Interestingly, I am totally intolerant to gluten and dairy and giving those up also improved it.
My arms are scarred after 46 (I couldn't remember my age then and had to think for a while!) years of having it, so they will never look totally clear. They feel a lot smoother these days though. I also find that over the last 5 years it's moved down to my lower arms and the backs of my thighs also.
I was sent to a dermatologist once in my late teens and they said I had localised acne and sent me on my way with no products or advice, but this was many years ago. I didn't have acne anywhere on my body and still don't, so they were talking utter rubbish. Shocking to think that back then dermatologists didn't seem to recognise the condition - or that was my experience at least.