See this post for more information!) For more about panthenol, click here. For more about glycerin, click here.
USING HUMECTANTS TO REDUCE TRANSEPIDERMAL WATER LOSS
"A lipid-rich cream without any humectant had no influence on TEWL (transepidermal water loss)..." (Page 679, this paper). Think about this for a moment. A cream without a humectant had no effect on transepidermal water loss. Meaning that you could make yourself a decadent body butter filled with exotic and expensive oils, and it would not slow down the water loss from your skin. So you aren't really treating dry skin without using some humectant. Just 2% sodium lactate or 2% sodium PCA (and so on) could be enough to prevent the TEWL that leads to try skin. Ponder this...then think about how you're going to make changes in the workshop next time!
"Increased sensitivity to nickel was also found when nickel-sensitive humans treated their skin with moisturizers without humectant, compared to treatment with moisturizer with humectant. On the other hand, areas treated with the glycerol-containing cream showed less reactivity to nickel than those treated with a cream without any humectant." (Page 679, this paper.) So we can reduce our response to irritants by using humectants in our products?
"Treatments with SLS (sodium lauryl sulphate) solution under occlusion significantly increased TEWL and decreased skin hydration as assessed by capacitance measurements....Thus, irritant contact dermatitis treated with glycerol application compensate for skin dehydration, favouring physiological process to restore water barrier function of the impaired skin." (Abstract, this paper) In other words, it appears that using glycerin can reduce the TEWL caused by irritation.
Having said this, this paper notes that "Ten days treatment of normal skin with 20% glycerin significantly increased skin corneometer values, indicating an increased hydration. However, our study failed to show an influence of glycerin on human skin, in terms of TEWL and skin sensitivity to SLS-induced irritation." Mind you, this paper is from 2001 and the one above is from 2008, so there could be changes in technology or other experimental parameters that makes a newer study more valid. But we do need to take findings with a grain of salt when they go against other findings.
So it is possible that we can reduce our sensitivity to some ingredients or things when we use products that contain humectants. Or perhaps not. I don't see a downside to using humectants this way, although we never want to make claims of this nature, regardless of how much science we have to back it up!
If you want to know more on this topic, read this paper for more information. And click here for more information on stratum corneum lipids.
"A pure liquid crystal system, produced by an all-unsaturated fatty acid mixture, allows a rapid water loss through the bilayers with a moderate barrier action. The solid system produced with an all-saturated fatty acid mixture causes an extreme water loss due to breaks in the solid crystal phase. Maintaining the balance between the two phases is required for optimal barrier function in preventing water loss...Prevention of SC lipids phase transition by glycerol has been shown. Application of 10% glycerol to a mixture of SC lipids in vitro inhibited the transition from liquid to solid crystalline phase, even if the water content in the media was reduced to 6%. As glycerol does not act as humectant at such a low humidity, the authors concluded that in a dry environment glycerol effects can be explained by influencing SC lipid phase transition." (Page 28, this paper).
In other words, it seems like glycerin keeps our lipids in a nice balance of liquid and solid, so we don't get too much water loss from either direction. So even in dry environments, glycerin is a good choice for our products as it keep our stratum corneum lipids in balance.
I think it's safe to say that there are reasons for using humectants that aren't about attracting water from the atmosphere, so those of us with really dry skin still have a good reason to include them in our products! So let's take a few days to see how we can incorporate humectants in products for all skin types, but especially dry skin!
Topical Use of Dexpanthenol in Skin Disorders, Am J Clin Dermatol 2002; 3 (6): 427-433
The clinical benefit of moisturizers, JEADV (2005), 19, 672-688
Skin hydration: a review on its molecular mechanisms (Journal of Cosmetic Dermatology, 6, 75-82)
Glycerol and the skin: holistic approach to its origins and functions (DOI 10.1111/j.1365-2133.2008.08643.x)
Effects of glycerol on human skin damaged by acute sodium lauryl sulphate treatment (click here)