302 JOURNAL OF COSMETIC SCIENCE
Per TSA regulations, liquid cosmetics and personal care items are restricted to only 3.4 oz
or less in a passenger’s carry-on bag, while liquids over 3.4 oz are only permitted in checked
baggage.2 Since there are weight limitations and extra fees for checked baggage, travelers
frequently bring only carry-on luggage and, therefore, must abide by the TSA’s carry-on
regulations. Purchasing travel-sized (i.e., 3.4 oz or smaller) products after already purchasing
full-sized cosmetic and personal care products can be expensive and inconvenient, especially
when major retailers such as Walmart and Amazon sell a wide variety of generic travel-
sized containers to transfer products in, often marketing them as “TSA-approved.”
Sunscreens are over-the-counter drugs in the United States that provide photoprotection
against harmful ultraviolet (UV) radiation to prevent sunburn, aging, and skin cancer.
Skin cancer, caused by UV radiation, is the most common cancer in the United States,
affecting more than 9,000 people per day.3 Therefore, daily use of sunscreen is essential,
and sunscreens are often packaged when traveling.
Inorganic sunscreens have gained popularity over chemical sunscreens in the United
States over the past five years due to the combination of legislative changes, safety and
environmental concerns, and content created on social media. Under a recent rule proposed
by the Food and Drug Administration (FDA) in 2019, only zinc oxide (ZnO) and titanium
dioxide (TiO
2 )are considered generally recognized as safe and effective (GRASE) in
sunscreens.4 Inorganic sunscreens have also been gaining traction among social media users,
with over 151.3 million views under hashtags #mineralsunscreen, #inorganicsunscreen, and
#physicalsunscreen on TikTok5, while hashtags #chemicalsunscreen and #organicsunscreen
have 34 million views. Additionally, the term “mineral sunscreen” has been searched up to
376% more on Google than “chemical sunscreen” over the past five years.6
It is crucial that sunscreens maintain their integrity over time and keep their consistency,
aesthetics, and performance the same. While transferring sunscreens to alternative packaging
may seem trendy or convenient when traveling, it may change their overall stability, safety,
and efficacy. The aim of this study was to evaluate and compare the stability, quality, and
performance of inorganic sunscreen emulsions containing ZnO, TiO
2 ,and a combination of
ZnO and TiO
2 as UV filters in plastic (P), glass (G), metal (M), and silicone (S) packaging
during 12 weeks at 2 different temperatures (25°C and 45°C). To our knowledge, this is the
first study that focused on the stability of inorganic sunscreens and evaluated four different
types of packaging.
MATERIALS AND METHODS
MATERIALS
Three commercial sunscreens currently on the market were purchased from
Amazon, including Coppertone® Pure and Simple Kids SPF 50 containing ZnO
in 24.08% (Lot #TN00CD0, Beiersdorf, Stamford, CT), Ombrelle® Kids
Sunscreen Lotion SPF 50+ containing TiO
2 in 15 %(Lot #20W20Z, Garnier,
Montreal, Canada), and Banana Boat® Sport Sunscreen Lotion SPF 50+ containing
ZnO in 4.5% and TiO
2 in 6.5% (referred to as combination, Lot #210425117,
Edgewell, Shelton, CT). Table SI shows the ingredients in each sunscreen. The
intention of selecting sunscreens that were all SPF 50 was to test and compare
sunscreens with the same amount of protection. Additionally, caprylyl methicone
(Dow, Midland, MI) was used to dilute the sunscreen samples to evaluate particle
size.

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