High-throughput sequencing to analyze changes in the human scalp microbiome during the use of a shampoo.

Shampoo, a crucial personal hygiene product, holds significant economic importance. Given the complex interactions of the scalp microbiome and its impact on scalp and hair health, understanding how shampoo affects this ecosystem is vital. Results showed that 28-day shampoo use significantly increased scalp moisture content (P = 0.04) without affecting sebum secretion P = 0.23. Regarding the bacterial community, while alpha diversity indices showed no significant changes, the relative abundance of Proteobacteria was decreased significantly, and the relative abundance of Actinobacteriota was increased significantly; the relative abundance of Cutibacterium genus was increased significantly, from 11.58 to 28.66%, more abundant than Staphylococcus genus (from 16.55 to 18.37%). For the fungal community, the Chao 1 index decreased significantly, and the relative abundances of several phyla and genera changed, but retained the core microbiome (Malassezia). Canonical correspondence analysis revealed that the microbial communities shifted from an oily environment to a more moisturized environment. Network analysis showed different co-occurrence relationships between core taxa and physicochemical factors for bacteria and fungi. Functional prediction via PICRUSt2 and FUNGuild indicated that the shampoo altered metabolic pathways of bacteria and the trophic modes of fungi. In conclusion, the study described the complex community dynamics of scalp microorganisms before and after 28-day shampoo use. The results will help improve the interactions among shampoo, scalp microbiota, and scalp physiology, offering valuable insights for the development of scalp and hair care products and strategies.