A quick review of The Inkey List's Vitamin C. I've been using this for a few weeks maybe. The Inkey List 15% Vitamin C and EGF Brightening Serum Epitensive is a plant-derived Epidermal Growth Factor, a signal peptide, which supports collagen production and elasticity of the skin. Mainly only in the morning when I am not wearing makeup. It contains a 15% concentration of antioxidant vitamin c to help even out skin tone, fade acne marks, erase dark â¦ The Inkey List notes that if you choose to apply products on top of this serum, you should wait for 10 minutes to allow EGF to do its job. You'll read why below. The Inkey List 15% Vitamin C and EGF Brightening Serum is one of the best vitamin c serums and one of the brightening serums overall. Comes in a squeeze tube and when you're done you can cut it open. Price: $ Very affordable price point. Packaging: effective and simple. One of the main reasons why I got it.