world cancer report - iarc

Climbing plants on trellis at end
reduces indirect UV radiation whilst
admitting cooling breezes.
Side flap
reduces indirect
UVR
Means of sun protection include the provision
of shade that falls in the right place at
the right time of day (Fig. 4.13). Shade barriers,
which may be either structures or
trees, need to be of sufficient size, and provide
at least 94% protection against direct
ultraviolet radiation [9]. Natural shade is
attractive because of its aesthetic appeal,
cooling effect and fewer disposal problems
than with built shade. Advantages of the
latter include the precision with which
shade needs can be met and other uses
including rainwater collection and solar
power generation. Provision of adequate
and appropriate shade requires planning,
an aspect of which is a “shade audit” to
determine the adequacy of existing shade.
Planning additional shade requires consideration
of safety, site usage patterns, climatic
conditions, aesthetics, sightlines and
the possibility of vandalism.
Most summer clothing provides protection
factors against sunburn of greater than 10;
more than 85% of fabrics tested have protection
factors of 20 or more. Factors that
affect the protection offered by fabrics
against sunlight include weave, colour,
weight, stretch and wetness [10]. By comparison
with other options, scant attention
142 Prevention and screening
Low reflective soft fall matting
Front extension
increases size of
shaded area
Low reflective
grass surface
Fig. 4.13 Structural and other design features of a garden shelter designed to provide protection from
exposure to the sun.
is given to sun-protective clothing in relevant
groups [11].
Sunscreens are available worldwide as
consumer products; the European Union
and USA account for 75% of the world
market. Sunscreens are regulated either
as cosmetics (European Union, Japan,
South Africa and South America) or as
drugs (USA, Canada and Australia).
Investigations of sunscreen usage have
included determination of who uses them,
in what circumstances are they used, why
sunscreens are used, and what has been
the experience of users. It is evident that
sunscreen usage affects other sun-related
behaviour, such as deliberate engagement
in sun exposure, the duration of such
exposure, and the duration of incidental or
intentional sun exposure [12].
Sunscreens absorb ultraviolet radiation
across the 290-400 nm spectrum.
Efficacy is expressed through the “sunscreen
protection factor” (SPF) which is
the ratio of the least amount of ultraviolet
energy required to produce minimal erythema
on skin protected by the sunscreen
in question to the energy required for the
same effect on unprotected skin. Most
commercial preparations are presented as
having SPF values of up to 15-20. “Active”
ingredients of sunscreens are the chemicals
included to reduce the amount of
ultraviolet radiation that reaches viable
cells of the skin. Sunscreen formulations
typically contain UVA absorbers (examples
being cinnamates and derivatives of
para-aminobenzoic acid) and UVB
absorbers (such as the benzophenones)
together with solvents, wetting and suspending
agents and preservatives [13].
Outcome
A range of end-points may be employed to
assess the efficacy of sun-protective activity
as a means of preventing skin cancer. A
high proportion of sun protection campaigns
incorporate some measure of outcome,
although few studies of large-scale
community interventions have been
reported. In assessing the results of particular
campaigns, it is important to consider
whether people change their behaviour
in ways that counteract the benefits of
a sun protection campaign [13].
The efficacy of particular interventions in
reducing risk of cancer has been most
comprehensively studied in relation to sunscreens.
Sunscreens undoubtedly prevent
sunburn. In experimental studies, sunscreens
have been definitively shown to
prevent squamous cell carcinoma induced
by solar-simulated radiation in mice. The
prevention of skin cancer in humans is less
clearly established, determination of the
issue being complicated by a number of
factors. These include the consideration
that use of the sunscreen may determine
(and perhaps even encourage) sun exposure.
Approximately half the relevant casecontrol
studies recently reviewed by IARC
(8/15) recorded significantly higher risks
for melanoma in users of sunscreens than
in non-users, while a minority of such studies
showed lower risk for melanoma in
users compared to non-users [13]. Some
findings imply that sunscreen use may
encourage prolonged sun exposure, a scenario
which obviously complicates
attempts to demonstrate protective
effects of sunscreens. In contrast to the
data concerning risk of melanoma, corresponding
studies in relation to squamous
cell carcinoma constituted “limited” evi-