I never thought that I would even mildly like a vitamin C serum in a clear jar. But Kiehl's Clearly Corrective Dark Spot Solution
) gets a semi-nod: it's likely to work, though not as well as concentrated L-ascorbic acid serums like Skinceuticals CE Ferulic.
It contains a stable form of vitamin C, 3-O Ethyl Ascorbic Acid, that fares better in the presence of light and air, plus vitamin E and a solid delivery system. Overall, I like it because it's likely to work, albeit slowly. Also note other products on the market are better for sunspots, including concentrated L-ascorbic acid serums and 4% hydroquinone. For more, read on.
3-O-Ethyl Ascorbic Acid
There are really limited studies on 3-O-Ethyl Ascorbic Acid. In fact, the semi-relevant one I could find was that 3-O-Ethyl Ascorbic Acid can help to inhibit the development of tumors when eaten by mice (European Journal of Cancer Prevention, 1998). But I digress. Here's the thing. All derivatives of vitamin C must first be broken down into L-ascorbic acid and another component in order to be active within the skin. Several companies sell L-ascorbic acid in concentrations up to 20%. So, you need more than 20% vitamin C derivative to end up with the same amount of L-ascorbic acid within the skin that the L-ascorbic acid serums provide. How much more depends on the specific derivative, the delivery system, the pH, as well as the 20% L-ascorbic acid serum in question.Kiehl's Clearly Corrective Dark Spot Solution is just one of many vitamin C derivative serums that fails to list the concentration of vitamin C derivative. (In fact, the only one I've seen is Perricone Ester C, with 15% vitamin C ester). If I had to give my best estimate, I'd say it is 10% 3-O-ethyl-ascorbic acid, which is anywhere from 5-7% active L-ascorbic acid within the skin. Not the strongest vitamin C I've ever seen - but it is substantial enough to work over time, albeit slowly.
Vitamin C derivatives have to be broken down into L-ascorbic acid + other component(s) before becoming active. So to have the same potency as a 20% L-ascorbic acid serum, a vitamin C derivative serum would need to have more than 20% vitamin C derivative.
Solid Delivery System
If I spent my early twenties learning about boys (and finally finding the right one!), I spent my late twenties learning about skin care delivery systems. I kid you not - just as the opposite sex can put you through the ringer, so can delivery systems. Contrary to popular belief, neither propylene glycol nor alcohol are harmful or detrimental to the skin in beauty products. Instead, they both help deliver key ingredients deep within the skin. Propylene glycol is incredibly effective in getting ingredients into the skin - so much so that it's the same ingredient used in nicotine patches. On the other hand, alcohol thins a solution, allowing the thick layers of a formulation to be compressed. If many skin care formulations didn't contain alcohol, they would rest on top of the skin, never delivering key ingredients. That's not to say you should use pure alcohol on your skin regularly - this would dry it out. But in the context of other ingredients, alcohol dries them out - not your skin. This is a mistake I made early on in my days at FutureDerm, and I'm sorry about the misunderstanding.
After applying Kiehl's Clearly Corrective Dark Spot Solution, my skin feels smooth and non-tacky.
Why is it in a clear bottle?
My other problem with Kiehl's Clearly Corrective Dark Spot Solution is that it is in a clear bottle. When it comes to light and air, vitamin C is one of the most reactive skin care ingredients out there. Sure, 3-O-ethyl ascorbic acid is certainly more stable than L-ascorbic acid, but I have studied many ascorbic acid derivatives, and none are completely unreactive to light and air. There's no need to provoke vitamin C in a clear bottle. A better option: a dark amber bottle (for Kiehl's) or placing Kiehl's Clearly Corrective Dark Spot Solution back in the box quickly following each use.
I know a lot of women who love Kiehl's. It's probably a combination of the fact that Kiehl's has some high-quality products, and that their marketing budget went way up after they were acquired by L'Oreal a few years ago. But I digress. I like Kiehl's too, so I will say this: If you want the best vitamin C or sunspot treatment on the market, don't buy Kiehl's Clearly Corrective Dark Spot Solution. But if you swear by Kiehl's and only want to use their products, then I will tell you that you will get results from Kiehl's Clearly Corrective Dark Spot Solution, albeit slowly. Product Rating: 7.5/10
- High or optimized concentration of independently proven ingredients: 2/3
- Unique formulation or new technology: 3/3
- Value: 2.5/3
- Sunscreen-boosting antioxidants: 1/1