Wednesday, January 13, 2010

The sunscreen rebound effect

I’ve just returned from a few days at the beach with my family. One thing that stands out as a key function of a parent in the summer beach environment is making sure your child avoids getting sunburnt.

This got me thinking about a world without sunscreen. This cheap little cream enables us to withstand sun exposure like super-humans, avoid painful sunburn, and partake in activities that would be out of the question in a 'no sunscreen' world.

Since sunscreen allows us to tolerate so much more exposure to the sun, is it actually contributing in some way to increased incidence of skin cancer? Are the net health benefits of sunscreen actually much lower because of our change in behaviour?

 How big is the sunscreen rebound effect?

There seems to be some acceptance of the sunscreen rebound. This article states that “Sunburn may even protect against melanoma - by keeping people out of the sun.

Again here:
The Australian experience provides the first clue. The rise in melanoma has been exceptionally high in Queensland where the medical establishment has long and vigorously promoted the use of sunscreens. Queensland now has more incidences of melanoma per capita than any other place. Worldwide, the greatest rise in melanoma has been experienced in countries where chemical sunscreens have been heavily promoted.
And here:
...sunscreen use tends to prolong the amount of time people spend in the sun while they are on vacation—and that only sunburn modifies the behavior of sun-seekers
And here:
Sunscreens suppress natural warnings of overexposure to the sun and allow excessive exposure to wavelengths ofsunlight which they do not block. Because sunscreens create a false sense of security, more effective measures to reduce sunlight exposure, such as limiting time spent in the sun or use of hats and clothing, may be ignored.
My experience suggests that all of these statements are true to some degree.

If everything was held constant - time in the sun, covered clothing, etc (notice the decline in hat wearing in the past few decades?) - then sunscreen may be quite effective at preventing skin cancer. But humans have a tendency to adjust their behaviour to take maximum advantage of such innovations.

The question that remains is whether there is still a net health benefit from sunscreen. But due to the plethora of uncontrollable variable in any longitudinal study, I'm not sure that we will ever have definitive statistical evidence for this.

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