New study by Rhoto reveals modified hyaluronic acid’s capability in restoring skin barrier function under dry conditions

Hyaluronic acid is a valuable functional ingredient for the skin. It occurs naturally in the human body and is found in high concentrations in the skin, joints, and eyes.

It helps maintain and regulate water balance in tissues and more importantly, acting as a lubricant and cushion in joints and hydrating agent in the skin.

In a collaborative research initiative, Rohto Pharmaceutical teams up with Saga University to examine the impact of hyaluronic acid on percutaneous absorption – how substances penetrate the skin relative to the applied amount.

The study involved the cultivation of a three-dimensional skin model for 14 days under varying conditions: normal conditions with a relative humidity of 95% or higher and dry conditions with a humidity of less than 60%. Alkylated hyaluronic acid was introduced daily starting from the third day.

Following the cultivation period, microscopic examinations were conducted on cross-sections of the skin model and corneocytes. Measurements were taken for both the thickness of the stratum corneum (i.e., outermost layer of the skin) and the area of corneocytes (i.e., cells on stratum corneum).

Influences of alkylated hyaluronic acid on the formation of skin structures  ​

Researchers observed variations in the state of the formed stratum corneum when conducting epidermal formation in a three-dimensional artificial cultured skin model under different humidity conditions.

In low humidity and dry conditions, the stratum corneum exhibited increased thickness and a looser structure, causing individual cell sizes to become uneven and larger. This suggest that the stratum corneum developed under dry external conditions, such as in winter, is more susceptible to peeling and lacks an adequate skin barrier function.

Upon adding alkylated hyaluronic acid during epidermal formation under these dry conditions, a thinner and denser stratum corneum was observed compared to conditions without the acid. This resulted in more uniform cell sizes, illustrating the formation of a more typical or normalised epidermis.

Future directions ​

In recent years, Rohto Pharmaceutical has delved into the percutaneous absorption behaviour of hyaluronic acid, examining differences in molecular weight and modification through a three-dimensional artificial cultured skin model.

The study’s findings unveil the pivotal role of alkylated hyaluronic acid in regulating stratum corneum formation and has discovered a new function of normalising stratum corneum formation under dry conditions.

Given the stratum corneum’s significance in skin barrier function, alkylated hyaluronic acid is considered beneficial for combating the diminished skin barrier function associated with dryness.

Encouraged by the results, researchers aim to continue the functional studies on hyaluronic acid, with a goal to develop formulation technologies that effectively harness the newly identified functions, propelling the creation of more satisfying products that address diverse skin concerns.

“As various modified hyaluronic acids are expected to have new functionalities beyond skin moisturisation, we will continue to work towards solving various skin concerns and developing products that satisfy our customers.”​ The researchers wrote.

The content of this research was presented and received the Poster Award at the 61^st​ Annual Meeting of the Japan Oil Chemists’ Society took place September 7 to 9,2023.