Endothelial and axon reflex vasodilatation to acetylcholine in rosacea-affected skin.

Rosacea is a chronic skin disorder, characterized by persistent painful facial flushing and often accompanied by papules and pustules. To investigate the mechanism of facial flushing in rosacea, acetylcholine was administered by iontophoresis to a 10-mm diameter site in the forehead of 31 patients with rosacea and in 29 controls of similar age and sex distribution. During the iontophoresis, current strengths doubled in eight steps from 2.5 to 320 μA. For each step, skin blood flow was monitored during 60 s of iontophoresis and for 2 min afterwards with laser Doppler flow probes at the site of iontophoresis and 5-8 mm away in the region of axon reflex vasodilatation. Vascular responses to acetylcholine were similar in patients and controls, but stinging sensations were greater in patients than in controls at the most intense current strength. In addition, axon reflex vasodilatation was greater in patients with severe than mild rosacea. These findings suggest that activation of nociceptive nerve fibres contributes to skin sensitivity in patients with rosacea, and that axon reflexes augment flushing in patients with the most severe symptoms.