Unilever introduced an improved version of Planta’s margerine. But as Planta’s sales curves soared, Dutch doctors began getting patients troubled by a strange and painful itch.

Early last month, when a splashy advertising campaign urged Dutchmen to “taste the improvement” in their favorite spread, thousands of housewives obediently followed directions. Most of them agreed that there was indeed something different about the new version of their old friend Planta, the good-eating margarine made by Van den…