91av

Winter is the season when the weather-worn British most envy Australians
and their seemingly inexhaustible supply of sun, sand and surf. But if the
focus of your envy is the proverbial bronzed Aussie, think again. For on
Bondi beach this summer life savers are wearing long-sleeved shirts, children
are sporting neck-to-knee ‘UV Zootz’, and young entrepreneurs armed with
spray guns are squirting sunscreens onto beachgoers who have forgotten to
bring their own.

The suntan is fast fading from fashion in Australia – and it isn’t hard
to see why. Rates of melanoma and other skin cancers have doubled there
over the past ten years, prompting a wave of hard-hitting health campaigns
about the dangers of UV radiation and heightening concern about the impact
that ozone depletion might have in the future.

These days, skin protection is all and sun-screen sales are booming.
A leading manufacturer estimated that Australians would spend about A $50
million ( £23 million) on sunscreens in 1993, with sales from pharmacies
up a hefty 30 percent over 12 months. This year Australians will use an
estimated 500 000 litres of sunscreen.

But behind the healthy beach scenes, researchers, doctors and manufacturers
are at loggerheads over the scientific basis of the claims used to promote
sunscreen preparations. Some specialists are dismayed at what they see as
the intrusion of commercial interests into public health issues, while others
are beginning to question whether sunscreens eliminate all the biological
damage that contributes to skin cancer. How these controversies are resolved
could affect sunscreen users everywhere.

The main row centres on SPFs, the numerical sun protection factors that
supposedly tell you how much protection the lotion provides. Members of
the sunscreen committee of Standards Australia, the independent body which
sets standards for the country’s sunscreen industry, are divided on the
meaning of SPFs and whether manufacturers should be allowed to continue
using them to label their products.

‘The current system of labelling by SPF numbers is a laboratory grading
which is misleading to the consumer,’ says Robin Marks, a dermatologist
and national spokesman for the Australian Cancer Society. ‘I don’t have
any problem with manufacturers saying their product filters out 99.95 per
cent of radiation, but I don’t think they should use the SPF rating in their
promotion.’ The rating system implies that sunscreens with an SPF of 30
are twice as good at protecting you from skin cancer as those with an SPF
of 15. But this is far from true, says Marks.

His reasoning follows from the way manufacturers measure SPFs. In the
procedure that is mandatory in Australia testers take 10 volunteers and
irradiate patches of skin – with and without sunscreen – using lamps that
simulate the ultraviolet spectrum of sunlight. The dose of UV radiation
is kept to a minimum, just enough to redden the skin and produce slight
sunburn. The SPF number comes from dividing the average time needed to burn
protected skin with the average time needed to burn unprotected skin. An
SPF of 8 means that, on average, the lotion slows down the burning process
by a factor of 8; in other words, that the sunscreen stops 87.5 per cent
of the UV light that affects the epidermal and dermal cells of the skin.

The Australian procedure is much more rigorous than those used in other
countries. In Germany, for example, manufacturers don’t bother to use lamps
that closely simulate sunlight, and one major British manufacturer doesn’t
even use human subjects. But despite the rigour of the Australian test,
the SPF numbers it produces suffer from the same hidden complication: people
don’t live forever. What is the point, asks Marks, of using an extra-high
SPF sunscreen that – according to conventional reasoning – can stave off
skin tumours for hundreds of years, when a sunscreen with a lower SPF (and
correspondingly reduced price tag) can offer a lifetime’s protection? Sunscreens
rated at SPF 15 reduce the risk of developing tumours to such a low level,
says Marks, that for all practical purposes they protect just as effectively
as SPF 30 sunscreens.

Marks bases his opinion mainly on animal experiments conducted in the
1930s and 1940s, which suggest that each person’s risk of developing a skin
tumour grows as their cumulative exposure to sunlight increases. ‘If you
halve the total dose of ultraviolet radiation to which you are exposed,
you double the time before onset of the tumour,’ says Marks. According to
this rule of thumb, regular use of an SPF 4 sunscreen will delay the onset
of a tumour by a factor of 4, and an SPF 15 sunscreen by a factor of 15.

Delayed action

Since the tumour induction time for squamous and basal cell carcinomas,
two common forms of skin cancer in humans, is at least 20 years, argues
Marks, an SPF 16 sunscreen would delay the onset of a tumour – if you got
one – until the age of 320.

Not necessarily so, says Gavin Greenoak, director of the Australian
Photobiology Testing Facility, which is supported by industry, and the University
of Sydney’s representative on the sunscreen committee of Australia Standards.
He argues that an ultra-high SPF is worth having because the relationship
between UV radiation and skin cancer is complex and unclear. Until it is
better understood, he says, public health advice should err on the side
of caution, and manufacturers should continue to produce sunscreens with
SPFs of 30 or higher.

‘Among skin cancers other than melanoma, experiments with mice have
shown that it is not only the total dose of UV, but also the rate, which
will have a bearing on the time of onset and the number of tumours induced,’
says Greenoak. If radiation dose rate could be confirmed to be an important
risk factor for skin cancer, manufacturers might be able to justify claims
that an SPF 30 sunscreen is twice as protective as an SPF 15 sunscreen –
for it would halve not only the total radiation dose but the rate at which
skin is irradiated.

The picture with melanoma is less clear. Can-cer of the melanin-forming
cells in the skin occurs in people of all ages, and often not on those areas
of the body most exposed to sunlight. Some experts believe melanoma is the
result of one-off high exposure to UV light, rather than cumulative exposure
over months or years, but research is hampered because no one has yet been
able to make sunlight cause melanoma in laboratory animals. If, however,
melanoma is closely related to short-term high doses of radiation, regular
use of extra-high-protection sunscreens makes sense.

Most sunscreens available in Australia have SPFs of between 17 and 40,
but none can be labelled with an SPF rating higher than 15+. Some imported
products – such as the Bullfrog brand, popular among Australian surfers
– have SPFs in excess of 100, but they too are labelled 15+. Most other
countries do not have an SPF ceiling, although the US Food and Drug Administration
recently proposed a ceiling of SPF 30. The 15+ ceiling was imposed by the
Australian sunscreen committee partly to stop manufacturers getting into
a ‘numbers game’, and competing to produce the highest-rated sunscreen.
The committee also feels that ever-higher SPFs will encourage people to
abandon the hat and shirt, and rely solely on sunscreens.

Others point to a yet more fundamental question: how can we be sure
that sun-screens – even those with extra-high SPFs – really protect against
all the damaging biological effects of UV radiation, especially damage that
occurs in the absence of visible sunburn? UV radiation appears to cause
skin cancer in two ways: by damaging DNA in the skin’s cells, and by suppressing
the skin’s immunity to tumour cells (see ‘The resistible rise of skin cancer’,
91av, 16 May 1992). Researchers in New South Wales at the Royal
Newcastle Hospital showed in 1987 that human subjects exposed to UV radiation
from solarium lamps suffered a decline in their immune response even though
they were using an SPF 15+ sunscreen. Later experiments by the same team
suggest the decline is caused by UV-A radiation, which falls in a lower
energy band than UV-B.

Most sunscreens in Australia are now labelled ‘broad spectrum’, which
means they are supposed to filter out both the UV-B and UV-A regions of
the ultraviolet spectrum. But because UV-A radiation is of lower energy
than UV-B, its impact on skin tends to be swamped by UV-B’s effects, and
is therefore hard to measure. And even if there was an accurate way to measure
UV-A, it would not allay all concerns. Researchers at the University of
Pennsylvania in the US showed in 1980 that repeated daily doses of UV radiation,
especially UV-A, each too low to induce sunburn, had a ‘build-up effect’
and could produce sunburn on human skin after four or five days.

The most outspoken pessimist is Vivienne Reeve, a biochemist at the
University of Sydney, who says there is still a lack of compelling evidence
to support the view that sunscreens protect humans against skin cancer.
‘Mouse experiments show that sunscreens protect some from getting skin
cancer, but the mice are not exposed to the sunlamps in the same way humans
are exposed to sunlight. For example, the mouse only sees the sunlamps when
it’s wearing the sunscreen, but humans are exposed with and without sunscreen.’

Optimists, by contrast, point to a recent study by three Melbourne researchers,
Marks included, claiming regular sunscreen use can prevent solar keratoses,
discoloured spots which are a precursor of squamous cell carcinoma and
a risk factor for melanoma. In trials in 1991 and 1992 in Victoria among
50 people who already had solar keratoses, those who used a broad-spectrum
SPF 17 sunscreen every day during one summer developed fewer new keratoses
than an age-matched group who used a cream without sunscreen. They also
experienced more remissions.

Marks is encouraged by this trial. ‘We’ve been recommending sunscreens
for 20 years and this is the first time we’ve been able to show in humans
that these products have an effect on carcinogenesis,’ he says. But sceptics
such as Reeve see things differently. ‘Sunscreens have been around for quite
a while, but there’s been no slackening in the rate at which new skin cancers
are appearing,’ Reeve says. ‘So maybe we don’t really understand how sunscreens
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