Humectants: More about glycerin!
While researching the post on the possibility that glycerin might draw water from your skin in low humidity environments, I learned more than I could have possibly imagined about this plentiful and inexpensive humectant. I'd like to share a few of those findings with you. I know many of us avoid glycerin due it its stickiness, but I think after reading this, you might be willing to endure a little sugary sweetness on your skin to get these great benefits! (If you haven't read this post on an overview about our skin, please do so before reading this post as you might feel a bit lost with all these acronyms!)
Glycerin (aka glycerine or glycerol) is what's called an endogenous humectant, meaning it's part of the
natural moisturizing factor (or NMF) we have in our skin.
When applied to mice with deficient
AQP-3, only glycerin helped restore normal hydration in the stratum corneum, increased skin elasticity, and improved impaired barrier recovery. Other humectants, like propylene glycol, did not have the same effect. (Page 25,
this paper)
"In a moisturizers set of 10% urea, 10% propylene glycol and 10% glycerol in oil in water (o/w) emulsions, only the latter produced a significant increase of SC hydration. (Page 27, same paper). (And keep in mind, it could be that your dry skin is a result of mutated or lacking AQP-3, so glycerin might be a great choice for those of you with really dry skin!)
The effects of glycerin lasts well beyond the usage of the product containing it.
"Even in the wash-out period (2 weeks) after the end of application, the corneometry values of patients previously treated with glycerol-based cream remained higher than in the placebo group. Hence, glycerol exerts its hydrating effect not only on healthy skin but also in subjects with diseased skin primarily characterized by xerosis and skin barrier impairment." In other words, it keeps working even after you've stopped using it!
"Glycerol has been suspected to ameliorate dry flaky skin by facilitating the digestion of superficial desmosomes in subjects with dry skin." (page 675,
this paper) And glycerin "...possesses a keratolytic effect (revealed by desmosome digestion (p. 23,
this paper).
"Reduced activity of the corneodesmosome-degrading enzymes in dry skin results in retention of corneocytes on the skin surface and formation of scales." (page 23, same paper)
An aside..."Desmosomes appear as thickened patches in the cell membrane region between two cells.
Desmosomes contain specialized proteins–such as keratin (the same protein found in fingernails and hair), desmoplakin, and desmin filaments–that increase the rigidity of tissues. The most common type of desmosome–spot desmosomes–are found in epithelium, smooth muscle, and many other animal tissues. These are buttonlike junctions that bind cells together and also function as anchors for fibers in the cytoskeleton." (
This site)
In other words,
desmosomes bridge the space between adjacent epithelial cells and keep them connected. Glycerin can help to break these cells apart when they don't otherwise want to do so, which means we don't get those big flaky patches of skin but nice desquamation. This is a very convoluted way to say that glycerin can help exfoliate our skin by breaking apart these connectors and allowing our skin cells to shed.
Studies of mice with impaired sebaceous glands showed that the application of 10% glycerin twice a day for four days completely restored stratum corneum hydration, while the same application of sebum like lipids did not. (Page 25,
this paper)
To quickly summarize: It looks like glycerin can keep working to moisturize our skin for up to two weeks after we stop using it, it can help exfoliate our skin so it won't come off in giant sheets of dry skin, it can help restore stratum corneum hydration, and it could increase skin hydration and skin elasticity even in people with deficient AQP-3. Not bad for a really inexpensive humectant!
How should we use glycerin to get maximum results? "The moisturization effect of glycerol is depending on the quantity of absorbed humectant. Therefore, the concentration and the composition of the formulations are critical for a maximal benefit of glycerol treatment. A dose dependent improvement of SC hydration is characteristic for glycerol.
A rise in the glycerol content from 5% to 10% in an o/w emulsion improved the SC (stratum corneum) hydration and the protective effect against dehydration...In addition, on dry skin of the lower legs a dose-dependency of the hydrating effect was evidenced, with maximal benefit at 20–40% glycerol concentration.
However, application of undiluted glycerol results in dehydration of the skin, based on osmotic water extraction from the SC." (page 27, same paper)
In other words,
using 5% to 10% in the heated water phase of our product seems to be the ideal amount with the best benefits coming at 20% to 40% glycerin in a product. (I make a foot lotion with 25% glycerin that feels very sticky, but it feels like it takes my feet from really dry to amazing in one night! I put on a pair of socks and all is well!) It also says that don't just put glycerin on your skin because it could draw water out of your skin, which defeats the purpose. As we know, a
dding an occlusive ingredient to any product with glycerin will trap the water in, so let's follow the advice in the previous paragraph and in this post to include an occlusive ingredient with our glycerin and only use it in an oil-in-water lotion!
http://swiftcraftymonkey.blogspot.ca/2012/04/humectants-more-about-glycerin.html
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