Davin Lim, MBBS, FACD - Account Suspended says:Really depends on your skin sensitivities and the depth of rolling. From a safety point of view, start with say 0.25 mm roller, test patch the retinol and go from there. Derma rollers, much like DermaPen and SkinPen is a form of Collagen Induction Therapy or CIT. Rollers have needles of varying ...