Abstract
Dandruff is an unpleasant scalp disorder common to human populations. In this study, we systematically investigated the intra- and inter-associations among dandruff, physiological conditions such as sebum of the scalp, host demographics such as gender, age and the region of the scalp, and the microorganisms on the scalp. We found that the physiological conditions were highly relevant to the host age and varied in different regions of the same scalp. The sebum quantity and water content were negatively correlated with the formation of dandruff and had significant relationships with the two dominant but reciprocally inhibited bacteria on the scalp (Propionibacterium and Staphylococcus). The dominant fungus (Malassezia species) displayed contrary roles in its contribution to the healthy scalp micro-environment. Bacteria and fungi didn’t show a close association with each other, but the intramembers were tightly linked. Bacteria had a stronger relationship with the severity of dandruff than fungi. Our results indicated that the severity of dandruff was closely associated with the interactions between the host and microorganisms. This study suggests that adjusting the balance of the bacteria on the scalp, particularly by enhancing Propionibacterium and suppressing Staphylococcus, might be a potential solution to lessen dandruff.
Highlights
Physiological conditions could affect the microbial flora living on the scalp by affecting the scalp microenvironment
We investigated the effects of host demographics on the degree of dandruff (Table 1) as well as the relationship between dandruff and three physiological conditions (Supplementary Fig. S2)
We found that dandruff was associated with the interactions between the host and the microorganisms on the human scalp (Fig. 4)
Summary
Physiological conditions could affect the microbial flora living on the scalp by affecting the scalp microenvironment. The bacterium P. acnes can release free fatty acids onto the skin and promote bacterial adherence by hydrolyzing triglycerides and can produce bacteriocins to kill other strains[19,20]. Based on the results of previous studies, scalp dandruff could be affected by many factors, including the microorganism residents and many host factors. The associations of the severity of dandruff with the composition structure of the microorganisms, host demographics, and host physiological conditions and their interaction have not been clarified to date. We constructed an association network based on pyrosequencing data of the bacterial and fungal communities on human scalp samples with slight to moderate dandruff (but not severe scaling such as seborrheic dermatitis) to attempt to systemically analyze their relationships
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