kligman ingredient evaluation
- Glycerin is the chemical precursor for numerous processes in the skin, from cell differentiation to ____
- In skincare, it’s primary function is used to hold water (hydrate the skin) - how?
- Glycerin also has a property that weakens desosomes in dead cells, which helps slough (remove) dry / patchy skin
- Glycerin is the mother of all skincare ingredients, having been proven safe and effective over centuries of use. Despite its history, recent study has shown an incredible variety of properties and uses for glycerin. Many of these benefits have to do with it’s ___ - in this respect, Glycerin acts as a fuel to product more cells, and cell turnover is important to keep skin healthy. It’s also found in high quality cleansers as it’s one of the few ingredients that doesn’t wash off skin when added to a cleanser.
What is Glycerin?
Glycerin is discovered by Swedish scientist, C. W. Scheele discovered in 1779. Glycerin is also referred to as glycerol. It is a clear, colorless, odorless, syrupy, and hygroscopic liquid that could be made from a hydrosylate of olive oil. It is about 0.6 times as sweet as cane sugar and it is miscible with water and alcohol, slightly soluble in acetone and practically insoluble in ether and chloroform (1). It is one of the most widely utilized compounds in cosmetic formulations because of its effects on multiple targets and its universal applications. Its chemical structure brings together the stability of three carbon atoms with three water‐seeking oxygen atoms in an anisotropic molecule that is perfectly designed for use in skin and hair moisturizers.
Glycerin and its Cosmeceutical Benefits
Glycerin has a very well established importance in skincare products. Early studies have focused on its humectant and protecting properties. More recently, glycerin has been shown to modulate the phase behavior of stratum corneum lipids and to prevent crystallization of their lamellar structures in vitro at low, relative humidity (2). Incorporation of glycerin into a stratum corneum model lipid mixture enables the lipids to maintain the liquid crystal state at low humidity (2).
Glycerin is generally classified as a humectant; however, this characteristic is not the sole reason for its ability to achieve skin moisturization, in fact, it performs a number of different functions that are not directly related to its water‐holding properties. It also allows for the construction of different product physical forms that cover the spectrum from sticks to microemulsions to free‐flowing creams that maintain stability over time. The degree of purity to which glycerin can be manufactured not only ensures consistency and facilitates microbiologic stability, but also guarantees the minimization of allergic reactions by contaminants. The pure form of glycerin has been tested on thousands of patients and millions more have used it with extremely few reports of ill effects.
What are its benefits on the skin?
Glycerin can restore the suppleness of skin without increasing its water content, a trait that is exploited by its use in the cryopreservation of skin, tissue, and red blood cells, where water would freeze and damage them. It enhances the cohesiveness of the intercellular lipids when delivered from high glycerin therapeutic formulations, thereby retaining their presence and function. Furthermore, glycerin has been identified as a contributor to the process of desquamation, a critical component of the dermal renewal cycle, through its ability to enhance desmosome digestion. (3)
Glycerin remains the gold standard for moisturization. It is a prime candidate for facial moisturizer formulations due to the fact that it acts on so many different parameters with a nearly non‐existent side‐effect profile . It is also an excellent example of how moisturizer components, especially those used on the face, should be considered for their ability to enhance and protect the skin. Glycerin raises the bar for moisturizers in that it is capable of enhancing, or even rescuing, the intrinsic processes that are in place to maintain the orderly maturation of keratinocytes and the barrier function of the skin. (3)
Glycerin has been implicated in the molecular mechanism controlling keratinocyte maturation, an important aspect of normal desquamation and barrier maintenance. Furthermore, its role in the maintenance of hydration for the proper functioning of proteases, especially filaggrin, is critical to the successful treatment of eczemas (7,8). In general, the maintenance of the SC along with rapid repair of disruptions to the barrier that would otherwise become larger and increase inflammation and discomfort as well seem to be central tenets in the approach to treating potential dermatoses on the face with moisturization. Therefore, facial moisturizers may represent a valuable first‐line treatment option for many dermatologic diseases and confer a number of important therapeutic benefits that go beyond the surface of the facial skin and have a critical role in the molecular mechanisms that maintain healthy skin.
Other medicinal benefits of Glycerin
Glycerin can be used as a solvent, plasticizer, sweetener, lubricant, and preservative (4). The substance has also been given intravenously or by mouth in a variety of clinical conditions in order to benefit from its osmotic dehydrating properties (5). This effect can also be used topically for the short-term reduction of vitreous volume an intraocular pressure of the eye (5). Concentrated solutions of glycerin is also used to soften ear wax (6). Suppositories with glycerin can also promote fecal evacuation (5, 6).
In addition to its direct, humectant effects on skin moisturization, endogenously produced glycerin has exhibited effects at the molecular level in knockout mouse model studies, confirming its role in maintaining SC hydration and barrier maintenance. A recent study showed that glycerin content was three times lower, SC hydration was reduced, and barrier function was impaired in mice deficient in the water/glycerin transporter protein, aquaporin‐3 (AQP3) despite normal SC structure, protein–lipid composition and ion–osmolyte content. Glycerin, but not other small poly glycols, restored normal SC moisturization and TEWL values when applied to the AQP3‐deficient mice, confirming that glycerin was physiologically necessary in the modulation of SC hydration and barrier maintenance (9).
In vitro studies (10) have also shown that dry skin is generally stiffer than normal skin, and effective treatments such as with glycerin can indeed soften the skin. Extensive experimentation with glycerin (11) has shown that it moisturizes dry skin in a dose-related relationship dependent on the concentration of glycerin. It was postulated that the water- glycerin mixtures on the skin also assist in plasticizing the stratum corneum in a less than transient manner.
1 Budavari S. The Merck Index Rahway: Merck & Co., Inc., 1989
2 Froebe CL, Simion A, Ohlmeyer H, et al. Prevention of stratum corneum lipid phase transitions in vitro by glycerol—an alternative mechanism for skin moisturization. J Soc Cosmet Chem 1990; 41:51–65.
3 Draelos ZD Cosmetic Dermatology Second Edition, 2010
4 American Pharmaceutical Association and The Pharmaceutical Society of Great Britain. Handbook of Pharmaceutical Excipients. Baltimore: The Pharmaceutical Press, 1986
5 Reynolds JEF. Martindale: The Extra Pharmacopoeia. London: The Pharmaceutical Press,1993.
6 Zimmerman DR. The Essential Guide to Nonprescription Drugs. New York: Harper & Row, 1983.
7 Hanifin JM. (2008) Filaggrin mutations and allergic contact sensitization. J Invest Dermatol 128, 1362–4.
8 Presland RB, Coulombe PA, Eckert RL, et al. (2004) Barrier function in transgenic mice overexpressing K16, involucrin, and filaggrin in the suprabasal epidermis. J Invest Dermatol 123, 603–6.
9 Hara M, Verkman AS. (2003) Glycerin replacement corrects defective skin hydration, elasticity, and barrier function in aquaporin-3-deficient mice. Proc Natl Acad Sci USA 100, 7360-5
10 Missel PJ, Bowman WD, Benzinger MJ, Albright GB. An in vitro method for skin
preservation to study the influences of relative humidity and treatment on stratum
corneum elasticity. Bioeng Skin 1986; 2:203–214.
11 Bissett, D.L. and McBride, J.F. (1984) Skin conditioning with glycerol. J. Soc. Cosmet Chem. 35 345-350.