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Since so many people are starting to use The Ordinary here are what ingredients you CANNOT use together:
• Vitamin C + AHAs/BHAs
• Retinol + AHAs/BHAs
• Retinol + Vitamin C
• Glycolic + Salicylic acid
• Niacinamide + Vitamin C
Also, I cannot stress this enough USE SPF!!
• Vitamin C + AHAs/BHAs
• Retinol + AHAs/BHAs
• Retinol + Vitamin C
• Glycolic + Salicylic acid
• Niacinamide + Vitamin C
Also, I cannot stress this enough USE SPF!!
if you’re gonna use two that can’t be layered, use one in the evening and one at night. Anything with vitamin C is best used in the morning, retinol at night.
ok no one asked but quick lesson on AHAs + BHAs 
AHAs - used for brightening the skin, minimising pores & fine lines. The two most common ones are glycolic & lactic acid.
BHAs - used for oily/acne prone skin. Most common one is salycilic acid.
AHAs - used for brightening the skin, minimising pores & fine lines. The two most common ones are glycolic & lactic acid.
BHAs - used for oily/acne prone skin. Most common one is salycilic acid.
can I quickly just say, I know there are plenty of brands that have products that contain combinations of ingredients which contradict this list, but this advice is what’s been given by The Ordinary based on THEIR formulations
