Regulation of Plasma Substance P and Skin Mast Cells by Odorants

Background: Mast cells stimulate inflammation and itch sensation in the skin by releasing various mediators when they are activated. Stress exacerbates some skin diseases. We have reported that inhalation of certain odorants modulates immune reactions in the skin. Objective: The possible usage of odorants in the regulation of skin inflammation and itch sensation was to be examined. Methods: Female volunteers were subjected to interview stress with or without odorant inhalation. Mice were immobilized while inhaling odorants. Toluidene blue-stained sections were analyzed for activated mast cells. Plasma substance P level was determined by enzyme-linked immunoassay. Results: Interview stress induced plasma substance P only in volunteers who did not inhale odorants containing 2% 1,3-dimethoxy-5-methyl benzene (DMMB). Immobilization stress induced mast cell activation in mice and the activation was blocked by exposure to DMMB. Conclusions: Stress causes mast cell activation via an increase in substance P. The effect of stress is suppressed by inhalation of DMMB.