Hyaluronic acid is now recognized as one of the best moisturizing ingredients found in nature. It is widely distributed in various tissues of the human body and is also found in abundance between cells in the subcutaneous layer. For the skin, it acts as a water retainer and maintains skin elasticity.
Hyaluronic acid, as well as its sodium salt, sodium hyaluronate, are widely used moisturizing ingredients. Its ability to absorb up to 1,000 times its own body weight in water gives it unrivaled hydrating power. But in reality, hyaluronic acid is also a physiologically active substance that promotes tissue repair, cell protection and immune cell proliferation, among other things.
As powerful as hyaluronic acid is, there are some question marks. For example, can hyaluronic acid (or sodium salt) applied to the skin penetrate through the stratum corneum and be absorbed by the skin?
Those of you who have some knowledge of the molecular weight of hyaluronic acid will surely know that it comes in different molecular weights. It can be roughly categorized into:
- High molecular weight: greater than 1,800KDa
- Medium molecular weight: between 200KDa and 1,800KDa.
- Low molecular weight: less than 200KDa
In fact, hyaluronic acid’s ability to penetrate varies by molecular weight.
In 2016, Dr. Essendoubi, a French pharmacologist, published a paper in the prestigious dermatology journal Skin Research & Technology. He used Raman spectroscopy to track the penetration of hyaluronic acid (HA) in the skin. It was found that three different molecular weights of hyaluronic acid can be absorbed into the skin, but exhibit variability in skin permeability.[1]
In the figure, A control glycerol; B negative control water; C high molecular weight HA; D medium molecular weight HA; E low molecular weight HA.
The spectral image shows the signal of low molecular weight HA, which has a wavelength of about 100 lm (Figure E), while the wavelengths of medium and high molecular weight HA are about 50 lm and 25 lm, respectively (Figures C and D).
Based on this experiment, we can conclude that high molecular weight hyaluronic acid is mainly distributed in the stratum corneum, while low molecular weight hyaluronic acid can penetrate past the stratum corneum.
Hyaluronic acid can reach the dermis.
In 1999, Dr. Brown T J, an Australian biologist, and others proposed in the Journal of Investigative Dermatology that the skin has active transport capacity for hyaluronic acid, which means that hyaluronic acid does not penetrate through the epidermis by passive diffusion; the researchers labeled 250-400 kDa hyaluronic acid by the isotope of hydrogen 3H and found that hyaluronic acid can be transported from the skin surface to the dermis. Hyaluronic acid was found to be absorbed from the surface of the skin and to pass rapidly through the epidermis and into the deep dermis.[2]
Brown made tests on both human and mouse skin and found that hyaluronic acid can not only enter the epidermis, dermis, and lymphatic epithelium, but also found that the absorption is not limited to small molecules of hyaluronic acid, and the absorbed hyaluronic acid is completely metabolized to water and acetic acid in lymph nodes, liver and kidney, and a small portion of which is discharged through the kidneys, which will not cause any harm to the body.
Stanford Chemicals Company (SCC) is at the forefront of hyaluronic acid development, offering sodium hyaluronate powder in various molecular weights. For more information or specific applications, please visit our homepage.
[1] Human skin penetration of hyaluronic acid of different molecular weightsas probed by Raman spectroscopy [J]. Skin Research and Technology,2016,22(1):55-62.
[2] Absorption of Hyaluronan Applied to the Surface of Intact Skin[J]. Journal of Investigative Dermatology, 1999, 113(5):740-746.