Abstract
It is widely-accepted that maintaining the scalp in a good condition is important for growing healthy hair. However, no adequate evidence is available that shows how scalp conditions affect physical properties of hair. From the observation of 101 Japanese women's scalp condition, here we found that the severer the scalp problem is, the more sebum is secreted, and moreover, the less resilient the hairs are. Based on these results, we hypothesized that irritants derived from secreted sebum cause scalp problems accompanied by the release of inflammatory factors, which affect hair follicular cells and suppress expression of genes essential to healthy hair formation. To address this hypothesis, we employed human hair follicle cell cultures. In outer root sheath cells, lipid peroxide up-regulated inflammatory cytokines such as IL-1 and IL-8, which suppressed keratin-associated protein 5.1 (KAP5.1) in hair organ cultures. KAP5.1 is known as a key molecule for cuticle strength. Furthermore, in several plant extracts we found an inhibitory effect on the increase of inflammatory cytokines caused by lipid peroxide. Taken together, it is suggested that increased inflammatory factors associated with scalp problems—at least those due to sebumderived irritants—act on hair follicle cells to deteriorate hair formation by down-regulating gene expression of key molecules, resulting in attenuation of the tensile strength and resilience of newly formed hair fibers. This consequence can be prevented with several plant extracts by suppressing the increase in inflammatory cytokines at the first step.
