308 JOURNAL OF COSMETIC SCIENCE
white, crumbly curdles while the sample at 45°C solidified to brittle, light brown plates.
This was an obvious sign of instability.
At week 0, the combination sunscreen was bright white and shiny (Figure 1). After 12
weeks, the plastic, glass, and metal samples at 25°C and the metal sample at 45°C remained
Table II
Spreadability of Sunscreen in Plastic Packaging
Zinc oxide-based sunscreen
Time point Firmness (g) Hardness work
done (g.sec)
Stickiness (g) Adhesiveness (g.sec)
Baseline 8.62 ± 0.15 8.96 ± 1.14 −5.93 ± 0.20 −0.08 ± 0.01
25°C P 12 weeks 9.49 ± 0.86 9.56 ± 0.17 −6.68 ± 1.20 −0.08 ± 0.00
G 12 weeks 10.43 ± 0.35 9.73 ± 0.36 −7.40 ± 0.23 −0.08 ± 0.00
M 12 weeks 9.23 ± 0.50 9.02 ± 0.23 −7.17 ± 0.76 −0.08 ± 0.00
S 4 weeks 71.91 ± 5.96* 42.27 ± 3.26* −53.83 ± 3.51* −84.51 ± 2.82*
45°C P 12 weeks 9.08 ± 3.01 9.60 ± 0.62 −5.98 ± 2.42 −0.06 ± 0.04
G 12 weeks 7.45 ± 0.71 9.51 ± 0.180 −5.52 ± 0.95 −0.08 ± 0.00
M 12 weeks 7.45 ± 1.10 9.94 ± 0.69 −5.12 ± 1.65 −0.09 ± 0.00
S 2 weeks 29.2 ± 4.76* 15.00 ± 2.02 −13.48 ± 2.23* −28.81 ± 2.99*
TiO2-based sunscreen
Time point Firmness (g) Hardness work
done (g.sec)
Stickiness (g) Adhesiveness (g.sec)
Baseline 5.97 ± 0.20 8.28 ± 0.34 −4.14 ± 0.23 −0.08 ± 0.00
25°C P 12 weeks 7.10 ± 1.56 9.40 ± 0.66 −3.70 ± 3.18 −0.08 ± 0.00
G 12 weeks 8.27 ± 1.15 9.31 ± 0.27 −5.62 ± 0.75 −0.08 ± 0.00
M 12 weeks 6.23 ± 0.16 9.79 ± 0.49* −2.87 ± 2.43 −0.08 ± 0.00*
S -N/A N/A N/A N/A
45°C P 12 weeks 8.66 ± 0.06 9.96 ± 0.16 −7.07 ± 0.64 −0.08 ± 0.00
G 12 weeks 13.05 ± 0.15* 9.96 ± 0.23* −8.54 ± 0.59* −0.08 ± 0.00*
M 12 weeks 10.92 ± 0.44* 9.85 ± 0.25 −6.81 ± 0.87 −0.08 ± 0.00*
S – N/A N/A N/A N/A
N/A: products solidified and could no longer be tested.
Combination sunscreen
Time point Firmness (g) Hardness work
done (g.sec)
Stickiness (g) Adhesiveness (g.sec)
Baseline 12.84 ± 0.50 7.91 ± 0.29 −8.57 ± 0.48 −0.08 ± 0.00
25°C P 12 weeks 12.40 ± 1.71 9.59 ± 0.03* −8.02 ± 0.79 −0.08 ± 0.00
G 12 weeks 11.71 ± 1.30 9.61 ± 0.27* −7.41 ± 0.87 −0.08 ± 0.00*
M 12 weeks 14.70 ± 1.91 9.34 ± 0.26* −9.53 ± 0.54 −0.08 ± 0.00*
S 4 weeks 22.08 ± 2.38* 13.68 ± 1.17* −15.33 ± 2.15* −17.62 ± 2.60*
45°C P 12 weeks 12.55 ± 4.21 9.29 ± 1.11 −7.89 ± 3.25 −0.08 ± 0.01
G 12 weeks 7.98 ± 2.38* 9.60 ± 0.11* −4.91 ± 1.94 −0.09 ± 0.00*
M 12 weeks 15.24 ± 2.52 9.72 ± 0.28* −7.75 ± 1.02 −0.08 ± 0.00*
S 2 weeks 8.74 ± 1.41 11.57 ± 0.04* −3.72 ± 2.63* −0.04 ± 0.00*
Note: Results displayed as average ± SD.
*Significant change, p value 0.05.

309 CONSUMERS TRANSFER INORGANIC SUNSCREENS
aesthetically consistent and stable. However, the plastic and glass samples at 45°C displayed
varying amounts of separation where a mix of a colorless and yellow transparent liquid was
present on the top of the samples. These samples were considered unstable. The samples in
the silicone packaging at both 25°C and 45°C changed significantly the room temperature
sample slightly thickened and was excreting oils from its packaging, and the sample at
45°C became visibly thicker. These changes also indicated instability and would have a
negative impact on a consumer’s experience.
FREEZE-THAW CYCLES
Conducting freeze-thaw cycles indicates how a product can withstand extreme temperature
changes and is used as a quick indicator of product stability. This is especially important
when traveling, for example, as airplanes fly to altitudes with frigid temperatures. Sunscreen
separation is an indication of instability.
Figure 1. Sunscreens’ appearance at week 12, *week 2 for the silicone container with the TiO2 sunscreen.