Microbiome‐Based Assessment of Topical Scalp Product‐Associated Microbiome Modulation

ABSTRACT Background The scalp microbiome plays a crucial role in maintaining scalp health, yet few studies have examined how topical scalp cosmeceuticals affect bacterial and fungal communities. In this study we aim to investigate the impact of a scalp serum on the scalp microbiome and physiology. Methods In this 12‐week IRB‐approved study, changes in the scalp microbiome before, during, and after the use of a scalp serum were measured in 56 participants. The bacterial and fungal microbiomes were assessed using 16S rRNA and ITS2 amplicon sequencing and analyzed key scalp parameters such as scalp thickness, intensity, moisture and pH. Results We identified a significant increase in the bacteria‐to‐fungi load ratio after 4 and 12 weeks of product use relative to baseline, driven primarily by increased bacterial load. Fungal Shannon diversity also increased after 4 and 12 weeks of product use relative to baseline, while beta‐diversity analysis showed a significant shift in bacterial composition. Pairwise comparisons of the dominant taxa identified significant increases in Cutibacterium namnetense and Cladosporium sp. abundances, along with a significant increases in other low‐abundance species after 12 weeks of product use. Spearman's correlation testing identified a significant negative correlation between Malassezia sympodialis and scalp thickness, with additional nonsignificant trends linking microbial composition to hydration and pH. Conclusion In conclusion, this study suggests that topical treatments may support scalp health by respecting the balance of the scalp microbiome.