comparison
The Crystal Retinal ladder: which strength to start with
Which strength to start with, when to move up, and how to climb from 1 to 20 without the irritation that makes people give up on vitamin A.
Retinol 0.25% or 0.5% — which comes first?
The honest answer to skincare's most common either/or: almost everyone should start at 0.25%, and the reasons are more interesting than caution.