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Will the Ren product be better cause it's natural, is it gentle?
AHA's are alpha hydroxy acids such as glycolic and lactic acid. You most likely used a product that had 12% glycolic acid and had a reaction to it. The way AHA's work is they chemically exfoliate your skin and reveal new skin. Some people do have redness associated with AHA's, especially they are sensitive.
You may want to go with something a little more gentle if you have had sensitivities to AHA's. If you are wanting to lighten acne marks in a gentle way you may want to check out Caudelie VinoPerfect Serum. This helps to brighten the complexion and even out tone and I have seen it work wonders on acne scarring.
It is always beneficial to do a patch test with new products to see how your skin will react. If you are near a Sephora store, ask for a sample to see how it works with your skin. The Caudelie serum is very gentle yet also very effective.