Real-Time Investigation of Skin Blood Flow Changes Induced by Topical Capsaicin

Capsaicin induces a localized inflammatory process known as neurogenic inflammation upon its topical administration on the skin, due to the release of various neuropeptides from the cutaneous sensory nerve endings. In this study, we investigated real-time skin blood flow changes that occur in neurogenic inflammation induced by topical capsaicin by means of in vivo reflectance confocal microscopy. 27 healthy subjects (15 women and 12 men, mean age ± Standard Deviation: 22.62±4.47) were administered topical capsaicin solution (Capsaicin group) or immersion oil (Control group) on the dorsal side of their non-dominant hand. At different time intervals during administration (0, 10, 25, and 40 minutes), cutaneous blood flow was evaluated using reflectance confocal microscopy and compared between the two groups. Blood flow values were higher during topical capsaicin, with significant increase after 25 (P=0.0160, Dunn's multiple comparisons test) and 40 minutes (P=0.0132, Dunn's multiple comparisons test) after its administration when compared with the initial 0 min value. Furthermore, the differences in the blood flow changes between the two groups were significant at 25 min (P=0.0182, Dunn's multiple comparisons test) and 40 min (P=0.0296, Dunn's multiple comparisons test) after capsaicin administration. Reflectance confocal microscopy allows in vivo, real-time evaluation of cutaneous blood flow changes within the capsaicin-induced inflammation, and this method might serve as a research model to test neurovascular reactivity.