Prospective Efficacy of Cutotype-Specific Personalized Topical Postbiotic Emollients in Females: A Single-Center, Cluster-Based, Pre-Post, Nonrandomized Controlled Trial in South Korea

Skin, the human body's largest organ, hosts diverse microbiomes that regulate host immunity and maintain skin physiology [1]. With advancements in metagenomics sequencing [2], our understanding of microbial diversity and composition has significantly expanded. Its composition substantially varies between individuals; therefore, several studies have identified distinct cutotypes, or microbial sub-community clusters, in various ethnic populations [3]. Our previous study established a comprehensive set of criteria to classify South Koreans' cutotype into 12 groups, considering both biophysical characteristics and microbiome composition [4]. Each of the four skin groups—HL (high in tone/elasticity but low in oil/water), LH (low in tone/elasticity but high in oil/water), LL (low in both), HH (high in both)—is further stratified by age groups (young, 10–34 years; aging, 35–50 years; old, ≥ 51 years) [4].

Given the complex interplay between the application of skincare products and the skin microbiome, it has been a novel objective for skincare products to maintain the skin microbiome. A previous study underscored the positive role of Staphylococcus in increasing skin moisture, Rothia in mitigating inflammation, Cutibacterium in boosting nutrition, and Streptococcus in improving elasticity [5]. Skincare products tailored to an individual's cutotype may help address specific skin concerns more effectively by balancing the unique microbial system on the skin. Moreover, supporting the natural balance of the skin microbiome may further contribute to long-term skin health, maintaining the skin's protective barrier. Thus, we aimed to develop a microbiome postbiotic emollient, with different microbiome compositions for each cutotype, for Korean females with low tone/elasticity (i.e., LL and LH) and evaluate the effects of these products on skin hydration, elasticity, and tightness.

The mean age of the 126 participants was 45.06 (standardized deviation, 15.19) years, with ages ranging from 20 to 67 years. Baseline characteristics, such as sleep time, sunlight exposure, smoking, and phase of menstrual cycle, are detailed in Table 1. Improvements in skin hydration, elasticity, and tightness were observed across all age groups for both cutotypes (Table 2). The most significant increase in skin hydration was observed in aging LH, with a mean difference of 1.76 (95% CI, 1.25–2.28), whereas the greatest enhancements in elasticity and tightness were found in young LH (elasticity, 0.60 [95% CI, 0.33–0.87]; tightness, −1.03 [95% CI, −1.36 to −0.70]). Similarly, for LL, three age groups showed enhanced skin hydration, elasticity, and tightness. The most considerable increase in skin hydration was found in young LL (4.39 [95% CI, 2.52–6.26]), while aging LL exhibited the most significant enhancements in elasticity and tightness (elasticity, 0.72 [95% CI, 0.22–1.22]; tightness, −0.76 [95% CI, −1.25 to −0.27]). No significant safety problems were reported during the study, although 3.17% (4/126) of participants reported itchy skin after the microbiome emollient.

This study showed the efficacy of microbiome-based emollients tailored to specific cutotypes in improving skin hydration, elasticity, and tightness. The results underscore the potential therapeutic applications of such products in personalized skincare. However, these findings should be interpreted with caution due to several limitations. The lack of investigation into changes in the microbiome composition hinders the direct assessment of this emollient's impact on the skin microbiome. In addition, we only recruited females, limiting our ability to generalize the findings to broader applications. Moreover, due to the nature of the pre–post-test study design, selection bias, and time-related bias may influence the changes observed between pre- and post-tests. Last, although the short duration of the intervention (2 weeks) was chosen to observe initial short-term effects, longer-term studies are needed to assess sustained outcomes.

Based on our novel classification of skin types, we developed skin care products for each cutotype. The microbiome skin care products customized for LL and LH cutotypes appear safe and effective, with significant improvements in skin hydration, elasticity, and tightness across all cutotype groups; however, the short intervention period and small sample size limit conclusions on long-term effects, warranting further research. This study may serve as a milestone for future studies investigating the association between cutotype and skin health.

D.K.Y. had full access to all of the data in the study and took responsibility for the integrity of the data and the accuracy of the data analysis. All authors approved the final version of the manuscript before submission. Study concept and design: J.O., H.J.K., D-.G.L., and D.K.Y.; acquisition, analysis, or interpretation of data: J.O., H.J.K., D-.G.L., and D.K.Y.; drafting of the manuscript: J.O., H.J.K., D-.G.L., and D.K.Y.; critical revision of the manuscript for important intellectual content: all authors; statistical analysis: J.O., H.J.K., D-.G.L., and D.K.Y.; study supervision: D.K.Y. D.K.Y. supervised the study and served as a guarantor. J.O. and H.J.K. contributed equally. H.J., D-.G.L., and D.K.Y. contributed equally as corresponding authors. The corresponding author attests that all listed authors meet the authorship criteria and that no one meeting the criteria has been omitted.

The authors declare no conflicts of interest.