Review title is A Unique, All-In-One Serum [SEP] I was in the cosmetics and skincare business for 25 years and am very ingredient conscious. The makeup of this serum is truly impressive. It's also unusual to find one with Vitamin C and Retinol together in the same serum. This was my first time using this product and I was trying a new moisturizer as well so I did a controlled study. I washed my face and applied the serum alone. My face turned very red and hot like a bad sunburn. I washed it off, applied straight aloe Vera gel to calm my skin and left it on overnight. By the next morning all was well so I cleansed my skin as usual and applied the new moisturizer (which was also by Elrique Naturals) and the same thing happened. Needless to say both products were extremely uncomfortable to use. Comparing the ingredients I don't see anything listed on either product that would cause this. I first suspected Niacinimide (Vitamin B3), but it's not listed. It's possible that the Vitamin C was too strong for my skin but there is none in the moisturizer. I have no issues with Retinol so that's not it. The reasons why Elrique Naturals did not agree with my skin will have to remain a mystery.