# Management of Scalp Biofilm in Local Dermatosis: From In Vivo Visualization to Optimal Treatments
## 4 Discussion
Epidermal cells require oxygen to produce ATP; however, because the epidermis lacks blood circulation, the process depends on oxygen diffusion from the atmosphere [54; 55]. The reliance of keratinocytes on direct oxygen diffusion from the atmosphere results in a constant state of mild hypoxia within the epidermis [56]. The presence of bacteria on the epidermis could potentially worsen the level of hypoxia in this tissue because of the oxygen consumption by bacteria, even if it is highly concentrated in one area [57]. Biofilms develop quickly on the scalp skin and use up oxygen in the tissues below [58]. As a result, the colonization of the skin leads to the formation of localizedbiofilm communities, which then deplete oxygen from the underlying skin tissue, leading to apparent damage to the keratinocytes throughout the skin [53]. Recent progress in the analysis of microbial gene sequences on normal skin has led to an extensive understanding of the types of microbes residing in different locations on the skin and their diversity [59]. Pioneering research has delved into shotgun sequencing methods to further investigate the taxonomic diversity and geographical distribution of microbes in small groups of healthy individuals [60]. Commensal skin microbes maintain an adaptive skin immune balance by interacting with specific subsets of antigen-presenting dendritic cells (DCs) and effector T-cell populations, consequently supporting their own survival and safeguarding against the proliferation of pathogens [61; 62]. For example, commensal skin microbes are linked to disease flare-ups in AD, which serves as a model of an atopic/allergic inflammatory disease [63]. However, the association of distinct microbial classes with biofilms on the scalp affects host physiology and causes inflammatory skin diseases, such as seborrheic dermatitis, atopic dermatitis, and psoriasis [64]. In this study, we developed an in vivo method to visualize biofilms on the scalp using erythrosine; these biofilms strongly depend on the bacteria and fungi present on human scalp. The physiological properties of the scalp significantly differ with respect to staining-positive subjects, for whom the sRA rarely decreases, and staining-negative subjects, for whom it does not. The sRA shows a medium-to-strong positive correlation with IL-8 levels and sebum production. In particular, we conclude that sebum production has a dominant effect on the scalp microbes, which leads to the formation of biofilms, as observed by changes in the sRA. Moreover, we decreased the sRA using antimicrobial agents such as CBZ and HD and the physical properties of scrubs in scalp care products. We suggest that the evaluation of scalp biofilms could be of assistance in understanding scalp physiology and investigating new approaches for the development of therapeutic products for scalp health. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app142110008/s1](https://www.mdpi.com/article/10.3390/app142110008/s1)]([https://www.mdpi.com/article/10.3390/app142110008/s1](https://www.mdpi.com/article/10.3390/app142110008/s1)), Table S1. RT-PCR primer sets, Table S2. Ingredient for hair care product and Figure S1. Individual images for _S. aureus_ and _C. acne_. Conceptualization, [PERSON]-[PERSON], [PERSON] and [PERSON]-[PERSON]; methodology, [PERSON]-[PERSON], J.K. and [PERSON]; software, [PERSON]-[PERSON] and H.R. ; validation, [PERSON]-[PERSON], [PERSON] and [PERSON]; formal analysis, [PERSON]-[PERSON] and [PERSON]; investigation, [PERSON]-[PERSON], J.K., [PERSON] and [PERSON]; resources, [PERSON] and [PERSON]; data curation, J.K. and [PERSON]; writing--original draft preparation, [PERSON] and J.K.; writing--review and editing, [PERSON], J.K., [PERSON] and [PERSON]; visualization, [PERSON]; supervision, [PERSON] and [PERSON]; project administration, [PERSON]; funding acquisition, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript. This research received no external funding.