Contact: Rebecca Spargo
BMJ-British Medical Journal
Does too much sun cause melanoma?
Is sun exposure a major cause of melanoma?
are continuously bombarded with messages about the dangers of too much
sun and the increased risk of melanoma (the less common and deadliest
form of skin cancer), but are these dangers real, or is staying out of
the sun causing us more harm than good?
Two experts debate the issue on BMJ.com today.
Shuster, a consultant dermatologist at Norfolk and Norwich University
Hospital, says that sun exposure is the major cause of the common forms
of skin cancer, which are all virtually benign, but not the rarer,
truly malignant melanoma.
Shuster says that the common skin
cancers develop in pale, sun exposed skin and are less frequent in
people who avoid the sun and use protection. In contrast, melanoma is
related to ethnicity rather than pigmentation and in 75% of cases
occurs on relatively unexposed sites, especially on the feet of
Africans. Melanoma occurrence decreases with greater sun exposure and
can be increased by sunscreens, while sun bed exposure has a small
inconsistent effect. Therefore, he concludes, any causative effect of
ultraviolet light on melanoma can only be minimal.
good evidence that the reported increase in melanoma incidence is an
artefact caused by the incorrect classification of benign naevi as
malignant melanomas, this, he argues, explains why melanoma mortality
has changed little despite the great increase in alleged incidence.
recognises that ultraviolet light causes the common, mainly benign skin
cancers and, like smoking, wrinkles the skin. But he says, this is not
a good enough reason for a blanket ban and we have to strike a balance
with the sun's many other effects on health—from psychological and
immunological, to the synthesis of vitamin D essential for bones and
apparent protection against many major organ cancers.
Professor Scott Menzies, from the University of Sydney at the Sydney
Melanoma Diagnostic Centre, argues that melanoma is far more common on
body sites receiving more sun exposure and in people of races who tend
to burn rather than tan.
According to Menzies, there is
considerable evidence that intermittent sun exposure and sunburn are
strong independent indicators of the risk of developing melanoma in
He argues that there is a clear association
between increasing cases of melanoma and increasing environmental
ultraviolet light. Genetic evidence is also supportive, he claims, with
the major genes causing melanoma showing ultraviolet light "signature"
mutations, while people deficient in repairing ultraviolet light
genetic damage have a 1000 times greater risk of developing the disease.
points to data from Australia which shows that cases of melanoma among
young adults fell between 1983 and 1996 and this coincided with strong
public health messages to use sun protection.
examine the geographical, sun exposure and genetic evidence together,
sun exposure is clearly a major cause of melanoma, he concludes.