Kose Corporation (Headquarters: Chuo-ku, Tokyo; President and CEO: Kazutoshi Kobayashi) confirmed that there is a correlation between the number of skin resident bacteria and some skin conditions such as "rough skin," "large pores," and "strong redness" in people with more bacteria than those with fewer. This is a result of establishing a simple method of measuring the number of bacteria on the skin, and giving a new evaluation axis of "bacterial numbers" in addition to the indicator of the presence ratio of bacteria that has been common in skin research. The results of this study were published in the September 2023 issue of the Journal of the Society of Cosmetic Chemists of Japan (SCCJ Journal) and won the "Best Paper Award for 2023" in the same journal in May 2024. ※
※Page of the Journal of the Society of Cosmetic Chemists of Japan (SCCJ Journal) where the excellent paper award was published

Background of the study

Skin has invisible resident bacteria, and in the field of skin research, it has been common to analyze the types and presence ratio of resident bacteria using genetic analysis technology. In healthy skin, these resident bacteria form a skin microbiome with a unique ratio for each person, and it is known that the existence ratio of these bacteria does not change much even before and after using moisturizer for one month (Figure 2). Therefore, it was considered that the resident bacteria ratio has limitations in explaining skin conditions. In this study, we focused on the "number" of skin resident bacteria and investigated the relationship with skin condition by establishing a method of measuring them.

Establishment of a method for measuring skin resident bacteria

As a method for understanding bacterial numbers, we first considered counting them by culturing as an existing method, but there was a problem with coverage because some skin bacteria are difficult to culture. Next, we considered using genetic analysis technology for analyzing the types of bacteria, but there was a challenge of lack of quantification due to the different numbers of target genes for each bacteria.
Therefore, we found a target gene called "tuf gene" that is common to bacteria and established a method of measuring skin resident bacteria with comprehensive and high quantification through repeated investigation of experimental methods.

Relationship between skin resident bacteria and skin condition

To investigate the relationship between the number of skin resident bacteria and skin condition, we collected part of the skin on the cheek of 269 general women aged 20 to 80 years old using the tape stripping method (a collection method for obtaining skin surface by attaching tape to the skin). When these were analyzed by the measuring method developed this time, it was found that the number of bacteria varies widely from several hundred to several hundred thousand per 1cm2 depending on the person, and there is a 100-fold difference in the number of bacteria between those with more and those with less (Figure 1). In addition, as age increased, the number of bacteria tended to decrease.

When we compared the skin condition of the top 53 people who had a lot of bacteria with that of the bottom 53 people who had less bacteria, we found that the roughness of the skin score was significantly larger and that the pores were larger. This may be because rough and porous skin makes it easier for resident bacteria to live. It was also found that people with more bacteria have more redness on their skin. This may be due to the fact that inflammation of the skin is easily triggered by resident bacteria or their metabolites. It was suggested that the amount of sebum, which is the source of nutrition for resident bacteria, is also larger in people with more bacteria. The amount of sebum is known to decrease with age, but it was also found in the age-specific analysis that people with more bacteria tended to have more sebum (Figure 3).

On the other hand, there was no correlation between factors that seem to be related to the growth of bacteria, such as stratum corneum moisture content and pH, and the number of bacteria. Therefore, it is considered that the effect of the number of bacteria on the face is greater than that of moisture content or pH, and that the number of bacteria, the number of pores, and the roughness (the degree of unevenness) of the skin are important factors in explaining skin conditions.
From these results, we can say that "bacterial numbers" are an important evaluation axis in researching the relationship between skin condition and skin resident bacteria.

Based on the results of this demonstration, Hitachi High-Tech and Hitachi will collaborate with various stakeholders such as material manufacturers including Sekisui Chemical to develop a more user-friendly environment and challenge One Hitachi to commercialize services using this system in Fiscal Year 2025. After the service is commercialized, Hitachi High-Tech will use its broad distribution network as a sales agent to expand to domestic and overseas product and material manufacturers. Companies (buyers and sellers) that participate in this business are being asked to join. Hitachi will work with Hitachi High-Tech and Sekisui Chemical to promote system development toward commercialization. Sekisui Chemical will continue to actively promote initiatives toward achieving a circular economy in 2050 by collaborating with Hitachi High-Tech and Hitachi.

From this study, it was found that the "number" of skin resident bacteria is an important evaluation axis in skin and bacteria research. Resident bacteria on the skin are beneficial for the human body because they produce moisturizing components to protect the skin and prevent the establishment of pathogenic bacteria by immune responses. We will continue to study the relationship between skin and resident bacteria and work on creating useful results for skin health in the future.