Retinol.

"This is going to be very hydrating. The next ingredient is niacinamide, which is a lovely combination because it strengthens the skin barrier, which is exactly what you want to do when you're using an irritating ingredient. [...] Plus they added adenosine, which is anti-inflammatory. Again, well done Kiehl's. I actually don't like a lot of products from Kiehl's, but they got it right with this particular product. I would say it's great for beginners to intermediate, but it is quite expensive at £72."

"The Kiehl's Retinol is a microdose formula of retinol that uses small percentages of retinol that slowly release over time, so you're not getting that irritation but you're still getting the efficacy you would see with retinol. It has peptides which are a really great complementing ingredient, especially when it comes to retinoids because they're very well tolerated but they also have some of the similar benefits in reversing photo aging. Similar to the CeraVe one, it also has ceramides which help to restore the skin barrier, moisturize and basically protect your skin while you're still having those benefits of retinol. I started using this year, really loved it, and it probably used it for several months without any signs of irritation at all and it would get on my eyelids I wouldn't get irritated from it which is fascinating for me because I have very sensitive eyelids. For people that are looking to get into retinols that are familiar with Kiehl's, Kiehl's kind of has a cult-like following, so if you like products from Kiehl's you tend to like other products from Kiehl's, so this is one of my favorite ones."