STABILITY OF PEDIATRIC SUNSCREEN EMULSION 379 is lower than the density of water. This interval was previously established in the labora- tory form the production and testing of three consecutive and identical batches of the emulsion. The values obtained were between 0.986 g/m3 ± 0.00153 and 0.993 g/m3 ± 0.00306. Figure 3 shows no changes in density over time or temperature variability, re- maining constant at values between 0.988 and 0.992 g/m3. PH Analysis of the pH of the emulsion gave values ranging from 7.233 to 7.253, and 7.223 to 7.247 for the towelette preparation. These values suggest that both formulations are suitable not only from a physiological, but also from technological point of view. The Neo Heliopan Hydro used in this study is a crystalline powder in acid-insoluble form, but on addition of neutralizing bases, such as triethanolamine, it becomes water-soluble. Consequently, the pH range must be kept within the range of 7.2 to 7.5 in order to main- tain hydrosolubility. The evolution of pH values versus time and temperature did not present signifi cant differences in any sample, and thus both towel and emulsion formula- tions were deemed suitable for topical application. MICROBIOLOGICAL CONTROL Figures 4 and 5 show that both formulations under study met the requirements dictated by the RFE (100 UCF). In the emulsion samples stored at 40°C from day 15, an increase in the number of CFUs was observed, but this increase was signifi cantly lower in samples obtained from the towelette preparation. RHEOLOGICAL CHARACTERISTICS Rheological assays to measure viscosity under different storage conditions and at different times indicated that both formulations showed a pseudoplastic behavior. During the time and conditions applied, the viscosity of the sample was maintained at values between 290,087 and 316,897 cps. Viscosity was determined in cps at a speed of 5 rpm. The re- sults obtained were the average of the three independent determinations. Figure 3. Evolution of density readings for the emulsion.

JOURNAL OF COSMETIC SCIENCE 380 A direct relationship between temperature and viscosity has been observed in other stud- ies, in which viscosity decreases with increasing temperature and vice versa (26). In our case, reference values obtained after 24 hours were 290 cps, 298 cps, and 303 cps at 4°C, 25°C and 40°C, respectively (Figure 6). Slight time-dependent variations in viscosity were observed, which were more pronounced just after preparation, but they gradually stabilized over time. However, changes were more evident in samples observed at 25° and 40°C. The slight variations that were ob- served at 4°C, could be attributed to an internal rearrangement of the formulation, and for this reason, storage temperatures of between 4° and 8°C are recommended. STABILITY The three emulsion samples were subjected to a centrifugal speed of 3500 rpm for ten minutes. No phase separation was detected at any of the predetermined time intervals, showing that the emulsion possessed good physical stability. Figure 4. Microbiological results for the towelette preparation. Figure 5. Microbiological results for the emulsion.