The role of Glycerin in skin care formulations

Introduction

Glycerin, also known as glycerol, has been used in cosmetic skin care formulas for the past one hundred years. In fact, it is in the top three most common cosmetic ingredients, after water and fragrance.

This widespread use is largely thanks to its valuable moisturizing and soothing properties, and of course its low toxicity. Also known by its IUPAC name, propane-1,2,3-triol, glycerin is comprised of three hydrophilic hydroxyl groups (-OH) on a 3-Carbon backbone. Hence, glycerin is a type of “polyol” – a chemical with multiple alcohol functional groups.

Those hydroxyl groups make this compound miscible with water. Not only that, glycerin is hygroscopic, meaning it has an affinity for water so high that it actually absorbs water from its environment. In just three days, glycerol will absorb its own weight in water! This property will prove useful as we take a closer look at how glycerin behaves on the skin.

Something appealing about glycerin as a topical agent is that it’s actually produced endogenously as well – that means it is produced naturally by our skin. Endogenous synthesis of glycerin occurs in the pilosebaceous unit, which includes the hair follicle, hair shaft, and the sebaceous gland. The role of our naturally-produced glycerin is to hydrate the skin and help regulate the skin barrier.

In this article, we take a look at the different roles glycerin may play in skin care formulas, including moisturization, regulating skin barrier function, enhanced penetration of other ingredients, and accelerated wound-healing.

Glycerin for dry skin

Remember that endogenous glycerin plays an essential role in skin hydration. Glycerol is distributed throughout the stratum corneum, or outermost skin layer. It has humectant properties that allow it to absorb water from the environment and lock in moisture.

Water is essential for the stratum corneum because it acts as a plasticizer, meaning it improves skin smoothness. Without adequate moisture, the enzymes naturally present in the skin cannot function properly. The stratum corneum requires anywhere between 15-40% water. If this number dips to 10%, the skin becomes dry and scaly – which is not only cosmetically unappealing, but unhealthy and can even be painful.

The medical term for dry skin is “xerosis.” Certain skin conditions that fall into this category may be associated with a genetic abnormality. Some people are more prone to dry skin than others, and external factors like dry weather can also play a role.

In such conditions, topical glycerin can supplement the lack of endogenous glycerin. It functions in the same way, by getting distributed throughout the stratum corneum and holding in water so that the skin is restored to its healthy function.

Glycerin for skin barrier function

The skin is your first barrier against environmental stressors. Lipids are especially important to the skin barrier. They exist in a balance between solid and liquid forms. The balance between those two phases is determined by the degree of saturation of the fatty acids (i.e., how many double bonds are present), among other potential factors. Think about coconut oil, a saturated fatty acid with no double bonds, compared to olive oil, an unsaturated fatty acid. Coconut oil is a solid at room temperature and olive oil is a liquid.

The lipids in your skin can also be solid or liquid. If either of these phases is in excess, the skin barrier cannot function properly and water is quickly lost from the skin surface.

Glycerol has been shown to influence the lipid phase balance, and is thought to improve the skin barrier function, especially in photoaged or otherwise compromised skin.

Glycerin for delivery of other skin ingredients

As discussed above, glycerin has a chemical structure that allows it to interact with the protective lipid layer of skin. An added bonus of this is that glycerin can be combined with ingredients that would not otherwise be able to penetrate the skin barrier. This makes it especially useful in cosmetic formulations.

Additional benefits

Some early studies show that glycerol may play a role in speeding up wound-healing, probably due to the aforementioned hydration properties and its ability to improve skin barrier function. It is even thought to have antimicrobial effects, which would further benefit wound-healing.

Preliminary work in non-human models suggests that glycerol could have a protective effect against UV radiation, but more research is needed.

Conclusion

Glycerin is an essential chemical that is produced naturally by the skin, and has also been used in topical skin care formulas for the past century. Because of its hydrophilic chemical structure, glycerin acts as a humectant that locks moisture into the skin, hence maintaining its hydration and optimizing skin barrier function. Additional benefits of glycerin may include accelerated wound-healing, antimicrobial properties, and protection against UV radiation.

References

Becker, Lillian C., et al. “Safety assessment of glycerin as used in cosmetics.” International Journal of Toxicology 38.3_suppl (2019): 6S-22S.

Fluhr, J. W., R. Darlenski, and C. J. B. J. Surber. “Glycerol and the skin: holistic approach to its origin and functions.” British Journal of Dermatology 159.1 (2008): 23-34.