If I take D3 without taking any retinol, I develop mild keratosis pilaris on the back of my arms (usually a sign of retinol deficiency) and it clears up quickly after adding retinol.
Keratosis pilaris (ker - uh - TOE - sis pih - LAIR - is) is a common, harmless skin condition that causes dry, rough patches and tiny bumps, usually on the upper arms, thighs, cheeks or buttocks.