Unexplained increases in skin cancer

A couple of weeks back I estimated the number of lives saved in New Zealand per year by the Montreal Protocol. Without it, the number of annual deaths would have doubled from around year 2060, with a continued rapid increases thereafter. Following that, my colleague Arjan van Dijk from the Netherlands passed on the bombshell plot below, which shows that since the 1990s, the incidence rates of skin cancer in the Netherlands have skyrocketed, and are now already about a factor of four greater than in 1990. He’s currently looking into updating the plot, and seeing how widespread the problem is. Is it just The Netherlands?

That recent rate of increase - for all types of skin cancer - is far faster than the predicted changes due to ozone depletion with or without the Montreal Protocol, as shown by the coloured curves above. Or as also discussed here.

There are several candidate possibilities to explain these increased rates. Arjan tells me about 30! The ones I can think of include an ageing population, changing lifestyles (including a more indoor lifestyle with occasional episodes of extreme UV exposures during summer vacations at holiday hot-spots), and improvements in diagnosis through increased public awareness of the issues. But the changes seem too large for any of those.

Perish the thought, could it also be related to increased sunscreen use? Although not proven, it has been suggested that earlier sunscreens that contained paraben may have led to increased risk from skin cancers. And harmful effects from assimilation of other chemicals in sunscreens have not yet been ruled out completely. I don’t think that’s the problem in New Zealand though because fortunately we haven’t seen correspondingly large increases in our rates of skin cancer since sunscreen use became more prevalent. But, perhaps another reason to use mineral-based products like zinc oxide that don’t get absorbed into our bodies….?…

It’s also been suggested that reduced levels of vitamin D due to sun avoidance practices may be exacerbating the problem. I don’t buy into that theory either, but more work is clearly needed to explain those increases.