SUN CARE
Organic versus inorganic sunscreens While the photodegradation of organic UV filters is commonly recognised and understood, the photoactive risks associated with inorganic UV filters are not well publicised. Eileen Zhang of Hallstar Beauty explains the differences between the two sunscreen filters and how to protect them.
O
insufficient to inhibit all their photoactivity. As a result, common inorganic sunscreens used today convey a false sense of security to the consumer.
DPPH monitoring test To reveal and monitor the photoactivity of inorganic filters, Hallstar proposed a test utilising the well-studied chemistry of DPPH (1,1-diphenyl-2-picrylhydrazyl), used as a free
rganic UV filters are a group of
There is a common misconception that
radical indicator. DPPH is a stable radical
carbon-containing compounds
inorganic filters are safer than organic
that scavenges other more reactive radicals.
designed to absorb UV
ones because they only reflect, scatter
When used in a solution, it has a deep violet
radiation. To maintain
and refract sunlight. Yet TiO2 and ZnO are
colour. When it reacts with and is neutralised
effectiveness over time, they should not alter
both semiconducting materials capable
by other radicals, the solution becomes pale
chemically after repeated UV irradiation.
of absorbing UV energy, which contributes
yellow to colourless.
Yet when many common organic UV filters
most of their UV shielding ability. After
absorb UV radiation and enter an excited
absorbing UV energy, these mineral
of 0.01 percent (w/w) DPPH were used to
state, they are often unable to release
particles become photoactive.
disperse TiO2 particles. The solution was
energy quickly to return to their ground state.
TiO2 and ZnO are well-known active
During a typical test, ethanolic solutions
irradiated under simulated or natural
This is when they are stable and ready to
photocatalysts used extensively in
sunlight. Solutions with a common
absorb additional UV energy.
heterogeneous photocatalysis to destroy
commercially surface treated TiO2 turned
Common inorganic sunscreens used today convey a false sense of security to the consumer
to pale yellow, indicating the generation of abundant free radicals. Yet when AvoBrite was added to the solution, it prevented the photogeneration of free radicals in a dosedependent fashion. This was indicated by
environmental pollutants that are organic
the different shades of DPPH in the presence
time in the sun, losing their absorption
in nature.1 When photoactivated by UV
of different amounts of AvoBrite.
capability and generating photoproducts,
light, they are known to generate highly
This test can easily be implemented in a
which haven’t been investigated
oxidising radicals such as hydroxyl (OH)
lab, giving sunscreen producers a quick way
for their safety on human skin. One
and other reactive oxygen species like
to evaluate the photoactivity and photo-
example is Avobenzone (INCI: Butyl
H2O2 and singlet oxygen, 1O2. H2O2 and
safety of inorganic sunscreens. To provide
Methoxydibenzoylmethane). Although it’s
1O2 are known to be cytotoxic and/or
the market guaranteed safety for inorganic
common and globally approved UVA filter,
genotoxic. OH radicals photogenerated
filter solution, Hallstar manufactures pre-
Avobenzone is notoriously unstable under
from photoactive TiO2 specimens extracted
protected inorganic dispersion products –
UV radiation. Hallstar, represented locally
from commercial sunscreen lotions induce
the HallBrite EZ-FLO TDX (TiO2 dispersion) and
by Millchem, was one of the first companies
damage to DNA plasmids in vitro and to
HallBrite EZ-FLO ZDX (ZnO dispersion) series. •
to discover its photodegradation and
whole human skin cells in cultures.2 To
dedicated many years of research to
restrict the photoactivity of inorganic UV
developing a range of solutions to stabilise
filters, all TiO2 and ZnO used in sunscreens
REFERENCES
the filter. The result was cutting-edge
needs to be surface treated. Unfortunately,
1. Nick Serpone, Daniele Dondi, Angelo Albini. Inorganica
photostabilisation products SolaStay S1
the quality of such treatment is not well
and Polycrylene, as well as the new China
controlled or monitored and is often
Unstable UV filters photodegrade over
Chimica Acta 360 (2007) 794-802 2. R.Dunford, A. Salinaro, L. Cai, N. Serpone, S. Horikoshi,
H. Hidaka, J. Knowland, FEBS Lett. 418 (1997) 87
compliant photostabiliser, AvoBrite.
Inorganic UV filters These are a group of mineral oxides such as titanium dioxide (TiO2) and zinc oxide (ZnO). They are often referred to as physical filters, making them inorganic.
The results of Hallstar’s DPPH test on TiO 2 , with and without the photostabiliser, AvoBrite
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| JULY 2019 | P C Review
ABOUT THE AUTHOR
Eileen Zhang is the global product manager for sun care solutions at Hallstar Beauty. She also leads Hallstar’s business development efforts in Korea, Japan, Australia/ Oceania and southeast Asia.
Hallstar – www.hallstar.com Millchem – www.millchem.co.za
