11'2 JOURNAL OF THE SOCIETY OF COSMETIC CItEMISTS Table V. Effects of Combining Preservatives on Effective Concentrations and Microbial Spectrum (Individual Preservatives Precede Preservative Mixtures) Anionic a Nonionic a Acid Alkaline Acid Alkaline Preservative -Result % Result % Result % Result % Bronopol S 0.05 U e 0.1 S 0.1 U e 0.1 Sodium Oreadinc S 0.1 U s.a 0.1 S 0.1 S 0.1 Bronopol q- S 0.1 S 0.1 U e,a 0.1 Ue, a 0.1 Sodium Oreadinc 0.05 0.05 0.05 0.05 Methylparaben q- S 0.15 U s 0.2 U a 0.2 Us,p, a 0.2 Propylparaben 0.04 0.05 0.05 0.05 Bronopol q- S 0.018 S 0.013 S 0.05 U a 0.1 Methylparaben q- 0.038 0.025 0.1 0.2 Propylparaben 0.009 0.006 0.0•5 0.05 Formaldehyde S 0.05 S 0.05 S 0.075 $ 0.075 Formaldehyde q- S 0.013 S 0.018 S 0.038 S 0.03S Methylparaben q- 0.05 0.075 0.15 I 0.15 Propylparaben 0.013 0.018 0.038 0.038 Gemsall U e,a 0.5 U c,a 0.5 U e,a 0.5 U e,a 0.5 Germall q- S 0.38 S 0.5 S 0.5 S 0.5 Methylparaben q- 0.15 0.2 0.2 0.05 Propylparaben 0.038 0.05 0.05 Us,l•,c, a 0.1 Methylparaben q- Us,e,a 0.1 Us,P,e, a 0.1 Us,v,e,a 0.1 0.02 Butylparaben 0.02 (I.02 0.02 U e 0.5 Germall q- S 0.5 S 0.5 Ue 0.5 0.1 Methylparaben q- 0.1 0.1 0.1 0.02 Butylparaben 0.02 0.02 0.02 0.2 MDMH NT NT Uc 0.5 U c 0.5 MDMH q- NT NT U c 0.,5 U e 0.5 Methylparaben q- 0.25 0.25 Propylparaben 0.05 0.05 Vancide 89RE U* 0.2 Up,e, a 0.2 Up,a 0.9. UP, a 0.2 Phenoxetol S 1.0 S 1.0 S 1.0 U* 1.0 Vancide 89RE q- U* 0.2 S 0.075 U* 0.2 U* 0.2 Phenoxetol 1.0 0.375 1.0 1,0 Preservative 68 U s 0.5 U s 0.5 Us,P 0.5 Us,v 0.5 Preservative 68 q- S 0.13 S 0.19 S 0.25 S 0.19 Formaldehyde 0.013 0.019 0.025 0.019 Symbols used: * = Organoleptic problems S = Satisfactory U = Unsatisfactory NT: Not Tested. Subscript figure denotes sin'rival of: s :- S. [aecalis p: P. aeruginosa c: C. albicans a = A. niger.

PRESERVATIVE REQUIREMENTS OF O/W EMULSIONS 113 tions. The level of preservative was reduced until the minimum inhibitory concentration for the most resistant organism was attained. The level that killed all organisms •vithin 7 days was considered to be the MIC. RESULTS Table II summarizes M[C data obtained on prescrvatives effective in one or more lotions. MIC data for preservative mixtures effective in one or more lotions appear in Table III. Those preservatives and preservative mixtures found to be unsatisfactory in all lotions tested are listed in Table IV. Organoleptic observations are included and noted as superscripts where applicable. •Ihey are explained at the base o[ the tables. In some cases (no- tably Vancide 89RE combinations), deterioration of aged lotions prevented further testing of lotions which were initially satisfactory. In preparing preservative mixtures, the basic approach taken was to com- bine t vo or more preservatives so as to eliminate gaps in m'•crobko_ogical spectrum, thereby accomplishing a complementary or synergistic mode of activity for the mixture. Table V presents data which illustrate this approach by comparing preservative activity of each compound when tested alone and when in combination. Only those combinations which show some kind of in- teraction are presented. Organisms unaffected by the preservative and/or the mixture are indicated by superscripts. Results of mixtures recommended by the manufacturers, such as Germall plus parabens, are also reported in Table V. Table VI summarizes the results of 174 preservation studies conducted on 4 lotion types. A total of 57 lotions (33%) were adequately preserved. Of these 57 lotions, 33 were anionic emulsions and 24 were nonionic. These results indicate a greater ease in preserving anionie emulsions. Acidic an- ionic lotions were satisfactorily preserved in 18/44 eases (41%) alkaline nonionic lotions were the most difficult to preserve of the 4 lotion types- 10/44 satisfactory (23%). Table VI Preservation According to Lotion Type Number Lotion Type Tested Acid anionic 44 Alkaline anionic 42 Total anionics 86 Acid nonionic 45 Alkaline nonionic 43 Total nonionics 88 Number Per cent Satisfactory Satisfactory __ 18 41 15 36 33 38 14 31 10 23 24 27 All lotions 174 57 33