how often should you use these skincare ingredients retinol 2–3x a week night only glycolic acid 3–4x a week night only vitamin c once a day morning azelaic acid up to twice a day morning and night salicylic acid 2–3x a week night panthenol 1–2x a day morning and night things to keep in mind retinol start slowly if you are new to it avoid using it on the same night as strong exfoliating acids if your skin is sensitive glycolic acid overuse can cause dryness and irritation avoid combining it with retinol on the same night at first vitamin c best used in the morning before sunscreen if it stings or irritates your skin try a lower concentration azelaic acid generally gentle enough for daily use reduce the frequency if you experience persistent stinging or dryness salicylic acid great for oily and acne prone skin using it too often can damage your skin barrier panthenol one of the easiest ingredients to use daily great for soothing and supporting the skin barrier you do not need to use every ingredient every day start slowly and increase only if your skin tolerates it