A total of 32 rosacea patients (25 with the papulopustular type of rosacea and 7 with the erythematotelangiectatic type) and 32 healthy persons were single-blind tested with a solution of 5% lactic acid and pure water applied to their cheeks. Twenty-four patients and 6 controls reacted positively as "stingers" (p<0.001) in this objective test of sensitive skin. All 7 of the patients with erythematotelangiectatic rosacea, but only 17/25 with the papulopustular type, were stingers (n.s.). The reason why some patients react with subjective symptoms, such as itching, burning, stinging, prickling or tingling, is unclear. The findings in this study are not surprising, but do support the theory that impairment due to different stimuli, most likely because of vascular sensitivity, is a central mechanism in the aetiology of rosacea. The correlation between sensitive vessels and sensitive skin has, however, not yet been determined.