Retinol 0.1%.

"For beginners wanting to start their retinol journey, you can't go straight to retinol 0.35. You have to start with something really mild. The COSRX Retinol 0.1 is a great retinol for getting started. The formula is so gentle. I have not heard of a single person I've recommended this product to physically, one-on-one, I've recommended this product to over 100 people, breaking out with this formula. If you generally have sensitive skin and you want to get started with retinol, or if you're just not sure what concentration will suit you, the COSRX 0.1 is truly one of a kind, very gentle formula. It is fabulous."

"The COSRX Retinol 0.1% I used solidly for about three months before they launched it, and I really, really enjoyed it. As someone with very easily irritated skin, this was amazing. I think also because of the Panthenol, it kind of really helped soothe my skin. Their product description says 'Low irritation with 0.1% pure Retinol', which is kind of rare to see in K-beauty. They say 'An irritation reduced solution created with the optimal ratio of key ingredients for first time Retinol users.' Which I think is perfect because a lot of people who are into Korean skincare often move to Korean skincare because they have very sensitive skin and the majority of K-beauty takes a gentler approach to a lot of their actives. So having a Retinol that is actually really good for first time users from a K-beauty brand that is actually huge in the rest of the world, I think it's a really good one to go for if you're new to Retinol."