Disclosed is a one-step permanent cosmetic composition that comprises 1.0 to 5.5 wt. % of a reducing agent; 0.1 to 9.5 wt. % of an alkaline agent; 0.1 to 7.0 wt. % of a catalyst; 1.0 to 15.0 wt. % of an alcohol; and distilled water or ion exchange water for the residual percentage by weight, using a solvent having an alkalinity (representing a consumption of 0.01 N HCl for 1 mL of a test sample) of 1.0 to 4.6 and having a pH value of less than 9.6; and also a one-step permanent cosmetic composition that comprises 1.0 to 5.5 wt. % of a reducing agent; 0.1 to 9.5 wt. % of an alkaline agent; 0.1 to 7.0 wt. % of a catalyst; 1.0 to 15.0 wt. % of an alcohol and additionally 1.0 to 4.5 wt. % of a viscosity enhancing agent; and distilled water or ion exchange water for the residual percentage by weight, using a solvent having an alkalinity (representing a consumption of 0.01 N HCl for 1 mL of a test sample) of 1.0 to 4.6 and having a pH value of less than 9.6.