Investigation of the Relationship between Skin Condition and Bacterial Counts by Establishing a Method for Quantifying the Bacteria per Unit Area of Facial Skin

Abstract

There are bacteria that cannot be seen by the naked eye on human skin. A predominance of Staphylococcus genus in the skin microbiota is known to worsen atopic dermatitis, indicating a relationship between the ratio or diversity of the skin microbiota and the skin condition. However, the skin is homeostatic and the specific bacterial ratio rarely changes in healthy individuals. We hypothesized that not only the ratio, but also the number of bacteria, can affect the skin condition. In this study, we collected skin microbes from the cheeks of 269 women, and determined the total number of bacteria per unit of skin area by performing quantitative polymerase chain reaction targeting the bacterial Tu（tuf）gene. We analyzed the relationship between the number of bacteria and various scores of skin conditions. Significant differences were found between the group with a high bacterial count and the group with a low bacterial count, i.e., the amount of sebum, pore count, texture count, dermis thickness, and redness level were higher in the high bacterial count group than in the low bacterial count group. These results suggest the possibility that the number of bacteria affects the skin condition. Thus, the total number of bacteria should also be examined when analyzing the relationship between the skin microbiota and the skin condition.