Chemical structures of potassium 2,5-dihydroxyphenyl sulfonate (DHPS: A) and potassium 2,5-diacetoxyphenyl sulfonate (DAPS: B). Panels C and D show representative images illustrating the effects of DHPS (C) and DAPS (D) on dermatitis of rat ears induced by the application of benzalkonium chloride. After induction of dermatitis in both ears, the right ear was treated topically with DHPS (5% w/v; eq. to 0.22 mmol/ml) or DAPS (5% w/v; eq. to 0.16 mmol/ml), and the left ear with the vehicle alone (glycerol). The extent of dermatitis (vascular hyperpermeability) was revealed by intravenous injection of Evans blue dye. In panel E the inhibitory effects of DHPS (5%; eq. to 0.22 mmol/ml) and DAPS (2.5% and 5%; eq. to 0.08 and 0.16 mmol/ml) on dermatitis are quantified, expressing the data as the mean ± SEM of the percentage of blue-stained area relative to the total area of the ear. The number of animals used for each determination is shown in parentheses: ***p < 0.001 vs. vehicle, † p < 0.05 vs DHPS by one-factor ANOVA followed by Student-Newmann-Keuls test.