Why is flushing limited to a mostly facial cutaneous distribution?
Despite the systemic nature of many agents that provoke flushing reactions, the erythema is most prominent in the "blush area." To elucidate the physiologic basis for such a limited distribution, two types of flushing challenges were studied in normal volunteers. Nicotinic acid provokes flushing through a direct action of vasodilator prostaglandins on vascular smooth muscle. The flushing reaction provoked by oral thermal challenge is mediated via neural mechanisms. Both agents led to increases in cutaneous blood flow at both malar and forearm sites. Both absolute and proportional increases were consistent with the view that the greater vascular capacitance in the visible, superficial cutaneous vasculature in the blush area accounts for the limited distribution of flushing in response to a systemic stimulus.