303 CONSUMERS TRANSFER INORGANIC SUNSCREENS
The packaging materials were also purchased from Amazon, including 2 oz clear plastic
bottles with flip caps (ZWLFLF), 2 oz clear glass jars with metal lids (Pinnacle Mercantile),
2 oz aluminum jars with lids (Yvjnxxan), and 2 oz soft silicone squeeze tubes with flip caps
(SYBL).
Plastic is the most common packaging for cosmetic and personal care products. Common
types of plastic include polyvinyl chloride, typically used for clear plastic bottles
acrylonitrile butadiene styrene, often used for sturdier compact containers and styrene-
acrylonitrile resin (SAN), typically formed into clear jars.7 The plastic bottle in this study
was made of polyethylene terephthalate (PET), and the cap of polypropylene (PP). PET is an
aliphatic polyester with great clarity, high flexibility, and good dimensional stability.8 PP is
a type of polyolefin that is physically sturdy and relatively chemically resistant with a low
density and high heat resistance.9 While clear plastic packaging is popular, transparency of
the container may allow light degradation of a sunscreen formulation.
Primarily derived from silicate, glass packaging is known to be impermeable to outside
contaminates and unlikely to react with the products it contains, making this packaging
type an ideal carrier for many cosmetic and personal care products.10 Additionally, many
consumers are turning to products in glass packaging not only because of the more
sustainable impact, but also because it enhances the consumer experience with its look
and feel.11 However, its brittleness, fragility, and transparency do not make this material a
practical option for manufacturers to produce. While amber or green colors are available
to account for light instability, transporting glass packaging is less cost-effective due to its
heavier weight and special handling.
Aluminum packaging is lightweight, cost-effective, flexible, and the most common metal-
based packaging material for cosmetics. While these properties may be advantageous,
other factors need to be considered, such as chemicals, like chelating agents, leaching into
the product, expansion of the containers in higher temperatures, and corrosion.12
There is very limited information on silicone packaging found in the literature. However,
a review by Colas et al. briefly discusses how silicone tubing used in pharmaceutical
applications can absorb ingredients with low molecular weight.13 The chemical composition
of the silicone tubing was not specified by the manufacturer, but this behavior aligns with
the results found in this study. Further research needs to be conducted on the composition
and properties of silicone packaging in a personal care context, especially considering
that “TSA-approved” products have increased in popularity and are easily accessible to
consumers.
METHODS
Stability testing. To evaluate stability, the sunscreens were transferred from their
original packaging to alternative packaging and placed into 25°C and 45°C stability
cabinets for 12 weeks. Each sample was tested for in vitro SPF, critical wavelength,
viscosity, spreadability, pH, particle size, and aesthetics at weeks 0, 2, 4, 8, and 12.
Additionally, each sunscreen underwent three freeze-thaw cycles in each packaging
type.
There is currently no enforceable protocol on how to test the stability of sunscreens
in the United States. The only requirement the FDA has for sunscreen stability is that
they maintain a shelf-life of three years, but it is the manufacturer’s discretion on how
to test

304 JOURNAL OF COSMETIC SCIENCE
this.14 Guidelines provided by The European Cosmetic Toiletry and Perfumery Association
(COLIPA), UL Prospector website, the International Council for Harmonisation of
Technical Requirements for Pharmaceuticals for Human Use (ICH), and experts in the
cosmetic industry influenced the design of this study.
In vitro SPF and critical wavelength testing. In vitro SPF and critical wavelength were determined
based on the FDA 2011 method using the Labsphere 2000S (Labsphere, North Sutton,
NH), described in detail in our previous work.15 Two plates were scanned per sample, with
a third scanned if the variability between the prior samples were too high.
Viscosity. Viscosity was tested in triplicates using a Brookfield DV-1 Prime Viscometer
(Brookfield, Middleboro, MA) with spindle 27 and a small sample adapter at 25°C.
Spreadability. The spreadability of each sample was tested under compression on the
TA.XTPlus Texture Analyzer (Texture Technologies, Hamilton, MA) using a TTC
spreadability probe. The pre-test speed, test speed, and post-test speed were set to 3 mm/s,
and the target mode was defined as distance of 1 1 m m. Approximately 8 g of each
sunscreen was placed in the sample holder. The pre-set location was assigned at 6.5 mm.
Each sunscreen sample was tested in triplicates at 25°C.
pH. The pH of each sample was determined using a pH meter (HANNA Instruments,
Smithfield, RI) in triplicates at 25°C.
Particle size. Particle size of 30 particles from each sample was determined using a light
microscope (Amscope, Irvine, CA) at weeks 0 and 12.
Evaluation of aesthetics. Aesthetics, including color, homogeneity, and signs of separation,
were visually observed at the above-mentioned testing intervals, and photos were taken at
weeks 0 and 12.
Freeze-thaw cycles. Each sample was placed in the freezer at -18°C for 24 hours, then thawed
for 24 hours at 25°C to complete one cycle. Samples were observed for signs of separation.
Data analysis. Statistical analysis of in vitro SPF, critical wavelength, viscosity, spreadability,
pH, and particle size were determined using one-way analysis of variance (ANOVA) followed
by Tukey’s multiple comparison test using SPSS Statistics 21 software (IBM, Armonk,
NY). A p value less than 0.05 was taken as the minimal degree of statistical significance.
RESULTS AND DISCUSSION
IN VITRO SPF
SPF values measured during the 12-week period were compared to the baseline SPF
and not the SPF claimed on the bottle. An important note is that it is not uncommon
for in vitro SPF to not exactly match the claimed SPF on the bottle. Studies have shown
that in vitro SPF values can be lower than what is claimed on the bottle.16,17 Some factors
that can influence in vitro results are the pressure applied to the polymethyl methacrylate
(PMMA) plate, the speed used to spread the sample on the PMMA plate, the storage
of the PMMA plates, or using multiple testers for the sunscreens throughout the study.
Consistency is crucial for reliable and reproducible results when testing in vitro, and these
were taken into consideration in this study by utilizing only one person to follow a standard
method, storing the plates in controlled conditions, and spreading the sunscreens for the
same period with consistent pressure.