Sunscreens
How do sunscreens work?
he fact that overexposure to the sun can
be harmful has been
well-publicised. A multitude of
authorities, including Cancer
Research UK and the
Department of Health,
recommend the use of
sunscreens as part of ‘sun safe’
behaviour (www.sunsmart.org.uk).
T
Mike Brown
Suncare Scientific
Advisor at Boots,
explains the science
behind sunscreens...
But how much do we understand
about what sunlight actually does
to our skin and how sunscreens
help combat its effects?
What does sunlight do
to the skin?
Most of the damage from the
sun comes from UV (ultra
violet) rays – UVA and UVB.
UVC in sunlight is completely
absorbed by the upper
atmosphere. UVB penetrates
into the outer layer of the skin
and damages the cells causing
the skin to be inflamed or
sunburnt. UVA rays penetrate
more deeply causing direct
damage to supporting tissues
leading to ageing effects. Both
types of rays are attributed to
causing different skin cancers.
How do sunscreens
work?
The main component of a
sunscreen product is the
UV-filter or filters. Their job
is to stop ultraviolet light from
reaching the skin. UV-filters can
do this in one of two ways: they
can either absorb the UV-light
by 'soaking it up'; or they can
scatter it and reflect it away
from the skin. Consequently,
there are two different types
of UV-filter and these are:
Absorber filters (organic filters)
Absorber type UV-filters work
by absorbing ultraviolet light
much like a sponge soaks up
water. Each tiny sunscreen
'sponge' soaks up ultraviolet
light, and then ‘drips’ it back out
after converting it into lower
energy and less dangerous
infrared light. These filters can
be thought of as ‘energy
converters', converting
dangerous ultraviolet light
into safer infrared warmth
(see below.)
Reflector filters (mineral or
inorganic filters)
Unlike the absorber type UVfilters, reflectors tend to be less
specific about the type of UVlight they reflect and tend to
protect against both UVA &
UVB. These sun filters act in a
different way. Instead of soaking
up the ultraviolet rays in the
way that the absorber sun filters
do, these materials reflect and
scatter the ultraviolet light away
from the skin without changing
it to anything else. They can be
thought of as thousands of tiny
mirrors each reflecting ultraviolet
light away from the skin.
The most commonly used UVfilters are the absorbers because
these are more efficient (you
get more sun protection for the
same amount of ingredient).
However they are often
supplemented with reflectors.
Sunscreens
However, some customers with
sensitive skin or maybe with
certain allergies may prefer a
product with less of these
absorber type filters in them. In
order to ensure that the product
still provides the required
amount of UV-protection, the
absorber filters are replaced with
reflector sunscreens. Allergy and
reaction to sunscreens is very
rare and so the large majority of
users find absorber type sun
filters suit their needs.
Because different UV-filters tend
to be effective against different
wavelengths of UV-light, most
sun protection products include
several different UV filters to
provide a broad spectrum of
protection across the whole
range of UV. Including multiple
different filters in the product
also helps to achieve the high
levels of sunburn protection
(the sun protection factor,
SPF value) that are demanded
by consumers today.
Another thing to know about all
sun filters is that many of them
will not dissolve in water. This
means that sun products must
contain oil ingredients to help
dissolve the sun filters. Manufacturers try to keep the oil content
to an absolute minimum to
prevent the finished product
from being greasy, but a small
amount in the product is essential.
New innovations
Sunscreen that will stay on
the skin for longer
Sunscreens are always
vulnerable to rubbing-off
whether by simple abrasion,
towelling or swimming and so it
has always been recommended
to reapply them every one to
two hours. However in recent
years new products which are
considerably more substantive
have been developed. These
novel longer lasting products
rely on new formulation tricks
to stay longer on the skin. Some
products incorporate ingredients
which facilitate penetration of
the UV-filters into the upper
layers of the stratum corneum
where they are protected from
being rubbed-off. Others use
active ingredients which attach
to the skin, whilst several rely on
the technique of embedding the
UV-filter in a continuous film of
water and abrasion resistant
material which binds tightly to
the skin. Whatever the
technology, the end result is a
product that continues to
protect for many hours after
application.
Antioxidant Sunscreens
As previously described,
sunscreen products work by
filtering the UV-light that reaches
the skin. But filters are exactly
that – a filter. So whilst they
filter out a large proportion of
the UV that falls on the skin,
they will inevitably let some UV
pass through and into the skin.
This UV can then interact with
natural components of the skin
and generate free radical
molecules which can then
damage vital skin components
through energy transfer
mechanisms. Antioxidant
ingredients can block these
energy transfers or neutralise any
free radicals that are generated
and thus provide a secondary
level of UV-protection.
New formats
Manufacturers are constantly
innovating around new ways of
presenting products. New
formats such as roll-ons and
sprays help make the experience
for the user easier and more
comfortable. Clear sunscreens
are an example of this type of
innovation.
Most sun creams are opaque,
i.e. they look creamy. That is
because they are ‘emulsions’.
Emulsions are made by mixing
oil-loving and water-loving
ingredients together (which
under normal circumstances
would not mix together), and
stabilising the mixture through
the use of special materials
called emulsifiers. UV filters are
usually either water-soluble or
oil-soluble and an emulsion will
contain a combination of these
filters. A transparent product can
be achieved if the formulation is
a single phase, i.e. not a mixture
that leads to an emulsion.
Transparent formulations have
been around for quite a long
time, BUT, the problem in the
past was that it was difficult to
achieve an even distribution of
UV filters on the skin, thus the
SPFs available in transparent
formulations have to date been
low, and previous examples
include the low SPF oils.
It is now possible to formulate
a ‘transparent’ or ‘clear’
sunscreen that is not only
non-oily but also one that offers
medium to very high protection.
It is possible to achieve this
through the use of special
polymers that allow for an even
distribution of UV filters on the
skin along with the use of an
effective combination UV filters
which are all soluble in water
or denatured alcohol.
The CTPA is the trade association for the UK cosmetic, toiletry and perfumery industry.
For further information on cosmetic products and their regulation, visit www.ctpa.org.uk