In this post, Weekend Wonderings: Adding Vitamin C to a product, Rosi asks: If vitamin C does not penetrate the skin, what is the benefit of it"
Good question! We use a lot of ingredients that don't penetrate the skin well, like hydrolyzed oat protein, carionic polymers, and oils, to name a few, and we know they offer great benefits.
I think we need to talk about what it means for an ingredient to penetrate our skin. Most ingredients will penetrate a layer or two of the stratum corneum, or the upper layer of our skin. Ingredients and products will mix with the natural moisturizing factor or the stratum corneum lipids to enhance moisturizing and hydration, assist with exfoliation, or create an occlusive layer. We can add ingredients to our products to help increase the possibility of penetration, called penetration enhancers. (Never ever do a search for that on Google!!!)
Molecules have to be very small to penetrate your skin - if I recall correctly, it's around 500 Daltons, which is very small - and very few of the ingredients we're using are that small.
But does Vitamin C have to penetrate our skin beyond the stratum corneum to do its magic" Vitamin C is a water soluble anti-oxidant has been proven in studies to be an anti-inflammatory that can stimulate collagen formation, lighten skin, treat hyperpigmentation, and heal wounds. It's water soluble ingredient that works best in creations with a pH of less than 3 (now that's acidic!) and concentrations up to 5% are well tolerated by our skin. It's present in every layer of our stratum corneum and it's essential for stimulating collage synthesis and the formation of the barrier lipids. Applying a lotion with a concentration of 5% over 6 months have been shown to improve the appearance of skin with photo-damage (and this isn't the "improve the appearance" like the cosmetic companies use this phrase - this was an actual study!) and it's been shown to reduce sunburn cel...