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