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When exposed to the sun, the skin's defences should
be supported by the use of a suitable sunscreen. The most essential
constituents of a sunscreen are the filter substances that act as
a shield between the sun and the skin.
Basically a distinction is made between physical and chemical UV filters:
 Physical UV filters
are inorganic substances. The UV radiation reaching their surface
is reflected and/or scattered and does not penetrate the skin. These
are normally mineral pigments, such as titanium dioxide. An important
new development is micronized pigments with a particle size between
10 and 50 nm. When present in a suitable base (cream, lotion), physical
light protection is not a cosmetic problem.
Chemical filters
are organic, aromatic compounds that can absorb UV radiation. Depending
on the wavelength absorbed one differentiates between UVB, UVA, and
broadband filters. The absorbed energy is emitted again as thermal
radiation.
Not all sunscreens prevent the emigration of the Langerhans` cells
and the dispersion of the systemic immunosuppressor interleukin 10
(IL-10). Sunscreens with the UV filter octyl triazone, such as the
products in the Eucerin® Sun Sensitive Skin series (Protective Lotion,
Protective Cream, Protective Gel, Anti-Ageing Face Cream, Protective
Spray, Children's Lotion and Children's Cream), protect the Langerhans`
cells of the epidermis from the immunosuppressive effect of UVB radiation,
thus guaranteeing an effective immune response.
A
medically effective UV protection is attained through a combination
of UVA and UVB filters (so-called broadband preparations) with the
addition of antioxidants, which reduce the formation of free radicals.
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According to W. Raab, 1993 Schematic diagram of
the effect of chemical UV filters and mineral micropigments.
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source: Schauder, S.,
Göttinger Liste, 1996 |
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UVB
protection factor:
The UVB protection factor (SPF) of a sunblock has been determined
since 1997 according to the COLIPA standard - a new, standardised,
Europe-wide method. The reproducable individual results measured demonstrate
the high reliability of the COLIPA method. This standardisation makes
it possible for users to obtain a comparable product performance with
the same UVB protection factor throughout Europe.
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Protection factor |
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UVA
protection factor:
Since the effects of UVA radiation on the skin are long-term, a generally
accepted method for determining a UVA protection factor is lacking.
For a long time no uniform standard existed. In Australia, the local
regulatory authorities developed a photometric process for estimating
the reduction of the UVA radiation, which delivers a reproducible,
reliable measurement. This standard (Australian standard AS 2604:93),
which is the only one of ist kind in the world, requires that sun
protection products absorb at least 90%. |
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UVA filtering according
to the Australian standard |
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Water
resistance:
Since water is permeable to UV radiation, a product´s protective capacity
in water - and its resistance to water - is of great importance. The
test of a product´s resistance to water, however, gives no indication
as to how friction affects the water-resistance of a product. Friction,
for example from towelling, can remove up to 80% of a sunscreen, leaving
it on the towel. After bathing, as well as after the subsequent drying,
even a waterproof sunscreen must therefore be reapplied.
A consistent, optimal photoprotection requires the combination of
effective, medicinal sun protection products and other measures such
as wearing of photoprotective textiles.
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Photostability:
UV filters can become unstable through the action of light and the
influence of skin enzymes, among other causes. Research has shown
that benzophenone, for example, displays a very high level of photostability,
while other filter substances such as octyl-dimethyl-PABA degrade
more quickly. Because of the trend towards using a high protection
factor in sunscreens, substances should be used that are also UV-stable. |
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SUMMARY:
To protect the skin from UV radiation, photostable UV filters
should be used in sunscreen products as much as possible. There
are two basic types of UV filters, physical and chemical. The
UVB protection factor (SPF) is determined according the COLIPA
method, and the UVA protection factor according to the Australian
standard. |
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more
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