I’ve always had KP on my arms, upper arms as well as forearms. Used various exfoliators, urea creams, glycolic etc. They helped but never eradicated it completely.
But about two months ago I started taking daily Vit D supplements (I use the Better You spray in the red bottle. Costs about a fiver) and I noticed about 6 weeks later, whilst idly stroking my arms, that all my KP had vamoosed. Nothing else in my routine has changed so this is the only thing I can put it down to. It's such a novelty for me having silky smooth arms.
Worth a try if anyone else would like to get rid of those pesky bumps.