Kao Analyzes Factors Influencing Hair Softness and Develops Softness Control Technology

- Stress at Slight Strain upon Touch to the Hair is a Factor Affecting Perception of Hair Softness.
- Stiff Hair from Damage Attributed to Reduced CMC*1 Flexibility Inside Hair Fibers. Glycylglycine Utilized to Soften CMC for Softer Hair.

The Beauty Research Center, Kao Corporation (President and CEO: Motoki Ozaki), has engaged in research on hair fibers from diverse perspectives from surface to the inner structure of hair fibers in pursuit of achieving beautiful and healthy hair. In the recent study, Kao analyzed factors affecting perception of hair softness and developed hair softening technology in response to consumers who were concerned about stiff and unruly hair.

Women feel hair softness upon casual daily touch, for example, when finger combing or adjusting the hair by hand. As a result of detailed study on fiber alignment and stress when finger combing, Kao identified that there occurred only very slight strain on hair tress (<0.5%) with these movements, but the subtle stress (i.e. less than five grams per hair fiber) influenced how women felt hair softness when touching their hair. Evaluation conditions for this research differed from those in the conventionally used evaluation method for hair tress (i.e. strain by more than approx. 1%; stress by more than five grams per fiber). Measurement of stress upon slight strain of hair enables evaluation of women's daily perception of their hair texture.

It is known that when damage is further developed due to ultraviolet rays, perms, hair color, and heat from the hair dryer, the hair becomes stiff and dry and thereby increases consumers' concerns about such hair texture. Kao found that reasons included the fact that lowered flexibility of cell membrane complex (CMC*1 ) between cortical cells, which form inner hair fibers, increases stress against slightly strained hair fibers upon touch. To counter that, glycylglycine was found to be a substance effective in softening CMC inside hair fibers to provide soft feel of the hair.
These research findings will be announced at the 16th International Hair Science Symposium "HairS' 09," held from September 9 to 11, 2009 in Weimar, Germany. At the same time, the findings will be applied to develop Kao hair care products for stiff or rigid hair.

Research Background

Concerns about Stiff Hair

In November 2008, Kao conducted a consumer fact-finding survey on stiff hair on 419 women living in the Tokyo metropolitan area. The survey revealed that 28% of them felt that their hair was stiff, and approximately 60% of them answered that they were "Very Concerned" or "Concerned" about their hair.

When damaged due to ultraviolet rays, perms, hair color, and heat from the hair dryer, the hair loses suppleness prompting consumers' concerns about stiff and dry hair, although the diameter of the individual fiber remains unchanged. This change is more obvious for coarse hair. Additionally, women with such damaged hair are concerned about their misaligned and unruly hair.

Based on these facts, Kao conducted the research with the aim of developing hair care products that enable these consumers to actually feel their hair softened.

Research Results

Stress at slight strain upon touch to the hair is a factor affecting perception of hair softness (Figure 1).

At a physical parameter evaluation of the hair softness, stress generated by strain on hair tress is measured. In the conventional method, measurement of slight stress was difficult; therefore, it was evaluated within a region where a hair fiber was strained by more than 1% and stressed with more than five grams per hair fiber. However, in reality, women feel their hair softness while engaging in daily casual touch to their hair, for example, when finger combing and adjusting the hair by hand. For this reason, Kao studied in detail fiber alignment, stress and strain on hair tresses upon finger combing.

As a result, it became apparent that through such gentle touching of hair, hair was exposed to imperceptible stress of less than five grams per hair fiber. With this level of minor pressure, the strain rate of the hair fiber was also very small or less than 0.5%. Measurement of stress at slight strain on hair tresses enables evaluation of the hair stiffness that women feel in their daily lives. Kao has named the region where only very little stress was generated by this minimal strain the "Slight Strain Region."

Stiff hair due to damage is influenced by reduced CMC flexibility inside hair fibers. For the solution, glycylglycine softens CMC for softer hair (Figure 2).

It is known that when damaged due to ultraviolet rays, perms, hair color, and heat from the hair dryer, the hair becomes stiff and dry prompting consumers' concerns about their hair texture. Kao has evaluated the damaged hair and confirmed that the hair feels stiff for the reason that the resistance in the "Slight Strain Region" is increased when the hair is damaged. Based on these facts, Kao analyzed factors that generate the subtle change of the resistance up to the cell level to consider solutions.

The hair fiber consists of a bundle of dozens of long, thin cells, called cortical cells, which are relatively hard cells, including crystalline protein. Cell membrane complex or CMC, a thin membrane organization comprised of protein and lipid exists between the cortical cells. To understand the micro structure of hair fiber, Kao studied the distribution of stiffness inside hair fibers through the "elastic modulus distribution measurement with scanning probe microscope*2 ," which can estimate the stiffness in a microscopic region.

As a result, it was found that CMC in the healthy hair is flexible, while that in the damaged hair became stiff. From these findings, Kao has clarified that CMC related to the physical parameters in the Slight Strain Region and reflected as a factor that influences perception of hair softness.

Furthermore, Kao studied technologies to improve the property in the Slight Strain Region in pursuit of healthy hair. The Company tested approximately 100 substances that are possible to work on CMC inside hair fibers, in terms of their functions affecting the Slight Strain Region. As a result, it was proven that glycylglycine functions to soften hair fibers. From the analysis of the mechanism of the action, it was confirmed that glycylglycine increased the CMC flexibility in the damaged hair fibers, which provided softness to the hair.

Additionally, damaged hair becomes unruly due to "meandering" or frizziness; however, since glycylglycine provides softness to the hair, flow of hair tends to be easily aligned during the process of hair drying, resulting in manageable hair. It was also clarified that when hair tress was aligned, the perception of hair softness was further enhanced.

*1 cell membrane complex between cortical cells which form hair strands

*2 By slightly stressing the surface of the samples with a micro probe for measurement of nanometer-order (one nanometer equals to one billionth meter), local stiffness is estimated. The distribution of stiffness can be grasped through repeated measurement by changing the stressing points with a probe in the target region.