164 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I I 8OO 6OO 400 2OO I I I I 0.2 0.4 0.6 0.8 PRESERVATIVE , ø/o Figure 2. Free formaldehyde in non-protein shampoos at 23øC as a function of preservative type and concentration. ¸, DMDM Hydantoin [•, Imidazolidinyl Urea /•, Imidazolidinyl Urea II +, Quater- nium 15. formaldehyde was also determined periodically during the 2-4 days required to reach equilibrium in the Conway dish both at 23øC and 60øC. There was no indication that formaldehyde was released faster at the elevated temperature.

FORMALDEHYDE IN SHAMPOOS 165 The amount of free formaldehyde released changes when protein is incorporated into the shampoo. The amount of free formaldehyde found at 23øC (Figure 3) is now depressed for all four preservatives as compared to the non-protein shampoo. The order of free formaldehyde measured is the same for all preservatives in the presence of protein as in the absence of protein. The relationships were the same at 60øC as at 23øC in 8OO 60O 4OO 2OO . '"" I I I I 0.2 0.4 06 0.8 PRESERVATIVE, % Figure 3. Free formaldehyde in protein shampoos at 23øC as a function of preservative type and concen- tration. O, DMDM Hydantoin g], Imidazolidinyl Urea A, Imidazolidinyl Urea II q-, Quaternium 15.

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