Discovery of a Turning Point in Skin Microbiome: Children's Skin Changes at Age 11.6?

Nippon Menard Cosmetic Co., Ltd. (3-18-15 Marunouchi, Naka-ku, Nagoya, Aichi; President: Junichi Nonogawa) conducted a study on the relationship between the skin microbiome and skin properties in healthy females aged 6 to 18. The results revealed that the balance of the cheek skin microbiome changes significantly around the age of 11.6. Furthermore, it was confirmed that in the 6-11 age group, higher bacterial diversity correlates with better skin barrier function, and in the 12-18 age group, a higher proportion of Cutibacterium acnes correlates with higher stratum corneum water content. This study suggests that the state of the skin microbiome changes with age, potentially significantly impacting skin barrier function and hydration. This achievement provides new insights into skin changes during childhood and adolescence from a microbial perspective and is expected to be applied in the development of future skincare cosmetics. Human skin is home to a diverse range of resident bacteria, including Cutibacterium acnes and Staphylococcus, which form the skin microbiome. Its composition is thought to change due to lifestyle, external stimuli, and individual differences, but research on the skin microbiome of minors has been limited, and its details were not fully understood. In this study, the relationship between the skin microbiome and skin properties was analyzed in healthy females aged 6 to 18. The results showed that the composition of the cheek skin microbiome undergoes a significant change at the age of 11.6. A detailed investigation before and after this turning point revealed that in the 11-and-under group, the proportions of Staphylococcus, Streptococcus, and Corynebacterium were higher, and higher bacterial diversity was associated with lower transepidermal water loss (TEWL), indicating better skin barrier function. In the 12-and-over group, the proportions of Cutibacterium acnes and Staphylococcus were higher, and a higher proportion of Cutibacterium acnes was specifically linked to higher stratum corneum water content. These results suggest that changes in the skin microbiome associated with growth may influence skin barrier function and hydration. Going forward, the company aims to develop skincare products focusing on the unique skin environment of each age group by clarifying the relationship between age-specific skin microbiome characteristics and skin concerns. The results of this study will be presented at the 125th Annual Meeting of the Japanese Dermatological Association, to be held in Kyoto from June 11 to 14, 2026. 1. Analysis of the Skin Microbiome Skin resident bacteria were collected from the cheeks of 24 healthy females aged 6 to 18 using a swab method, and the skin microbiome was comprehensively analyzed using a next-generation sequencer. The results confirmed that in the 6-11 age group, the proportions of Staphylococcus, Streptococcus, and Corynebacterium were high, while in the 12-18 age group, the proportions of Cutibacterium acnes and Staphylococcus were high (Figure 1). Figure 1: Proportion of each bacterium in the skin microbiome of each subject Furthermore, a segmented regression analysis for each bacterial species revealed that the turning point for the proportion of Cutibacterium acnes in the microbiome was 11.6 years of age, after which its proportion increased. Conversely, the proportions of Streptococcus and Corynebacterium decreased around the same time (Figure 2). These results indicate that the composition of the skin microbiome in healthy females changes at the turning point of 11.6 years of age. Figure 2: Changes in the proportion of each bacterium in the skin microbiome with age 2. Relationship between the Skin Microbiome and Skin Properties Based on the turning point of 11.6 years, where the microbiome composition changes significantly, subjects were divided into two groups: the 6-11 age group and the 12-18 age group. The relationship between the skin microbiome and skin properties was analyzed for each group. Analysis of the relationship between the skin microbiome and skin properties in the 6-11 age group revealed a negative correlation between the alpha diversity index (Shannon Index), which indicates bacterial diversity, and transepidermal water loss (TEWL), an indicator of skin barrier function (Figure 3). This means that higher bacterial diversity is associated with lower TEWL and a healthier skin state with better barrier function. Figure 3: Relationship between bacterial diversity and TEWL Furthermore, the Shannon Index showed a positive correlation with the proportion of Streptococcus, while showing a negative correlation with the proportions of Staphylococcus and Corynebacterium (Figure 4). Figure 4: Correlation between the proportion of each bacterium and alpha diversity (Shannon Index) These results suggest that in the 6-11 age group, appropriately controlling the balance of Streptococcus, Corynebacterium, and Staphylococcus to increase the diversity of the skin microbiome may lead to the maintenance and improvement of healthy skin. Analysis of the relationship between the skin microbiome and skin properties in the 12-18 age group revealed a positive correlation between the proportion of Cutibacterium acnes and stratum corneum water content (Figure 5). This indicates that a higher proportion of Cutibacterium acnes is associated with better skin hydration. Figure 5: Relationship between the proportion of Cutibacterium acnes and stratum corneum water content These results suggest that maintaining a skin microbiome where Cutibacterium acnes is dominant may lead to healthy skin in the 12-18 age group. While Cutibacterium acnes is commonly associated with acne, it inherently plays a crucial role in supporting the skin barrier by breaking down sebum to produce fatty acids and glycerol, maintaining the skin's slightly acidic pH to inhibit the growth of harmful external bacteria, and preserving skin moisture. On the other hand, excessive proliferation of Cutibacterium acnes due to factors like oversecretion of sebum can promote the production of inflammatory substances, leading to the development of acne with redness and pus. Therefore, maintaining an appropriate balance of the skin microbiome is crucial for preserving healthy skin. [Supplementary Material] Skin Microbiome in Adults* Skin samples were collected from the forehead and cheeks of 30 healthy individuals (15 females, 15 males; aged 24-48) using a swab method, twice in summer and winter. The skin microbiome was comprehensively analyzed using a next-generation sequencer. The results showed that Cutibacterium acnes was the most abundant bacterium, followed by Staphylococcus epidermidis, regardless of sex, body site, or season. *International Journal of Cosmetic Science Vol.45 No.3 Relationship between skin fungal and bacterial microbiomes and skin pH