While retinol is widely lauded as a versatile skincare hero, it may not be right for everyone, especially those with reactive or very sensitive skin. “Retinol can cause initial skin irritation, redness and flakiness, which may occur as the skin adjusts to the treatment,” says Dr. Phillips. There are a handful of retinol rules, too. Dr Phillips recommends avoiding excessive sun exposure and suggests using a high factor, broad spectrum SPF every day, as retinol can increase skin sensitivity to UV radiation. If you’re a retinol novice, Dr. Phillips recommends starting with a low concentration and gradually increasing frequency and strength to minimize the risk of irritation.