Hair styled in the morning becomes wavy again during the day: Focus on CMC damage inside hair caused by sunlight, potassium hyaluronate confirmed to suppress 'wave return'

Rohto Pharmaceutical Co., Ltd. (Head office: Osaka, President: Hidetoshi Segi) is advancing hair care research focusing on internal hair structure, addressing the hair concerns that customers experience daily. In this study, we focused on 'wave return' and analyzed the internal structure of hair using the 3GeV high-brilliance synchrotron radiation facility NanoTerasu. As a result, we confirmed that sunlight irradiation damages the lipid structure including CMC (cell membrane complex) inside the hair (hereafter, CMC damage), and that 'wave return' becomes more likely to occur under high humidity. Furthermore, while exploring materials based on our hyaluronic acid research cultivated in the skin care field, we discovered that potassium hyaluronate prevents sunlight-induced CMC damage and contributes to suppressing 'wave return' under high humidity. This research leads to a new 'texture control' concept that approaches hair manageability and texture from within the hair, addressing hair concerns caused by everyday environments such as sunlight and humidity. We will apply these findings to the research and development of hair care products.

*Wave return: The phenomenon where hair styled in the morning becomes wavy again over time.

Research Highlights

・A new perspective on 'wave return' research: Confirmed changes in internal hair structure due to sunlight. ・Confirmed that lipid structures including CMC are damaged by sunlight irradiation, making hair more prone to 'wave return' under high humidity. ・Confirmed that potassium hyaluronate prevents sunlight-induced CMC damage and suppresses 'wave return' under high humidity.

Background

Wave return, where hair styled in the morning becomes wavy again over time, is a common hair concern for many customers. It not only affects appearance but also leads to difficulty in maintaining hair manageability and styling. While research on wavy hair and the development of hair care techniques to control it have been conducted, the factors causing wave recurrence during the day have not been fully clarified from the perspective of internal hair structure. Therefore, this study focused on the effects of sunlight and humidity, investigating the impact of sunlight on internal hair structure, the relationship between these changes and wave return under high humidity, and searching for effective materials. Based on our hyaluronic acid research insights in skin care and customer feedback, we evaluated the applicability to hair.

Results

1. Sunlight irradiation causes changes in CMC, not IF Using NanoTerasu, we performed synchrotron X-ray scattering measurements to compare internal hair structure before and after sunlight irradiation. SAXS (Small-angle X-ray scattering) showed no significant changes in large protein structures such as IF fibers (intermediate filaments). In contrast, WAXS (Wide-angle X-ray scattering) revealed that a peak derived from lipid structure of CMC disappeared after sunlight irradiation, confirming that lipid structures including CMC are damaged by sunlight (Fig. 1).

2. Hair damaged by sunlight is more prone to wave return under high humidity CMC is an important lipid structure that controls moisture movement within hair. Comparing hair tresses with and without sunlight irradiation, when placed under high humidity conditions, sun-exposed hair tresses showed stronger waving and expansion compared to non-exposed tresses (Fig. 2). This is thought to be because damage to lipid structures including CMC due to sunlight disrupts the moisture balance inside the hair, making it easier for hair to swell under high humidity.

3. Potassium hyaluronate prevents sunlight-induced CMC damage and suppresses wave return under high humidity To search for effective materials that suppress wave return during the day, we compared various hyaluronic acids and found potassium hyaluronate as an effective material. Hair with damaged lipid structures including CMC due to sunlight irradiation is more prone to waving and expansion under high humidity. This study confirmed that using potassium hyaluronate suppresses sunlight-induced CMC damage and inhibits wave return under high humidity (Fig. 3, Fig. 4). Furthermore, we evaluated the penetration of potassium hyaluronate into damaged hair and its effect on hair stiffness (Fig. 5, Fig. 6). Results showed that hair treated with potassium hyaluronate suppressed hardening caused by sunlight irradiation.

Discussion

In this study, while no significant changes in IF fibers due to sunlight were observed, changes in lipid structures including CMC were found. These results suggest that wave return during the day may involve sunlight-induced CMC damage followed by high humidity environment. Furthermore, potassium hyaluronate was confirmed to prevent sunlight-induced CMC damage and suppress wave return under high humidity. This achievement leads to a new 'texture control' concept that approaches hair manageability and texture by focusing on internal hair structure, rather than just treating the surface, to address wave return that causes morning styling to collapse during the day.

Future Outlook

This research demonstrates new possibilities for approaching hair changes caused by daily environments such as sunlight and humidity from within the hair structure. Going forward, we will deepen research on 'texture control' technology from inside the hair using potassium hyaluronate, aiming for application in formulation design and product development. Combining insights cultivated in the skin care field with hair research, we will continue R&D of hair care technology that resonates with customers' real experiences.