To 50 ml of an aqueous solution containing 0.12% of methyl paraben and 0.01% (w/w) of propyl paraben preliminarily dissolved therein by heating to 80???-90??? C. (hereinafter, such solution is referred to as solution A), there is added 5 g of methylcellulose (Metolose 90SH 4000, Shin-Etsu Chemical Co.), and the mixture is stirred to prepare a dispersion.