EVALUATION OF COSMETIC PRESERVATIVE EFFICACY 325 to the sodium borate in this formulation. The predicted times for complete destruction of S. aureus, Bacillus sp. and P. aeruginosa were calculated to be 63, 30 and 6 hr, respectively. These times were corroborated by APC at 1 or 3 d. The antibacterial properties of this face cream and face cream samples containing different concentrations of the parabens were studied using S. aureus as the test organism. This is shown in Figure 2. Although the samples were taken immediately o 0 2 3 5 Hours Figure 2. Survivor curves showing the effects of different concentrations of parabens on the rate of death of S. aureus in face cream. Symbols: ©--© = face cream with no parabens (control), m--m = face cream with 0.12% methyl- and 0.08% propyl-paraben, and a•--, = face cream with 0.2% methyl- and 0.1% propyl-paraben.

326 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS after inoculation, the APC of the samples containing the parabens were lower than the APC in the control sample. This was not due to the order of sampling, because data for control samples were essentially the same when they were set up first or last. The D-values for the face cream control, the cream with the lower and the cream with the higher concentrations of parabens were 18, 4 and 0.6 hr, respectively. The times predicted for complete destruction of S. aureus in these samples were 63, 19 and 3 hr for the control, the face cream with the lower and the face cream with the higher concentration of parabens, respectively. This estimate was corroborated by APC of 10/ml at the 3-day sampling. The data shown in Figure 3 compare the antibacterial properties of hand lotion containing glyceryl dilaurate with lotion containing glyceryl monolaurate. The Hours Figure 3. Survivor curves showing the effects of substituting glyceryl monolaurate for glyceryl dilaurate on the rate of death of S. aureus in lotion. Symbols: ©--© = lotion with glyceryl dilaurate (control), and I--I = lotion with glyceryl monolaurate.