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Some sunscreens are not
stable when irradiated with simulated sunlight.
The photostability differs is very different for different
products. Two chemical sun filters have been tested for
their dark toxicity and possible toxicity to mouse cells
in a cell culture after UV-irradiation of the filters.
Increased
toxicity as result of breakdown
of a UVB-filter, octyl methoxycinnemate, was observed. UV
radiation absorbed in the filter will lead to the formation
of breakdown products that are different from the original
filter molecules and may have different toxicity and other
chemical properties.
The UVA filter included in the tests,
butyl methoxydibenzoylmethane, was also toxic in the dark.
However, it was more chemically stable to UV-irradiation,
and was not broken down efficiently by simulated sunlight.
Its toxicity did not change significantly
after irradiation.
It
can be concluded that the two sun filters in concentrations
of 5 -- - 10 parts per million are toxic in the dark to
mouse cells under our particular laboratory conditions,
and that the toxicity may increase after UV-irradiation
of the most unstable filter.
The biological role or medical effect
of these observations are not known and extrapolation from
the laboratory experiments to the use of sunscreens in humans
must be done with caution.
Radiat Prot
Dosimetry vol 91, p 83, 2000
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