Why is skin cancer more prevalent now than in ancient times?
When I was a kid, I spent every summer at the local pool. I was very tanned because there was no such thing as sunblock. I suspect things were pretty much the same throughout the entire history of mankind. Yet modern medical research tells us almost any exposure to the sun without protection could lead to skin cancer. Did societies such as the ancient Egyptians suffer from high rates of skin cancer, or are these alarms being sounded to help manufacturers sell more sunscreen?
[A rebuttal of this column appears at the end]
You seem to have been fortunate enough to avoid any experience with “black herpetic type lesions,” as Hippocrates described skin cancer circa the fifth century BC. Good for you and your leathery skin. But before you start slathering on the baby oil, consider this: the median age of onset for melanoma (the most deadly type of skin cancer) is 55, with the highest incidence rates found in the 65-plus demographic. I’d keep a closer eye on those irregularly-shaped moles if I were you.
There’s definitely cause for general concern: in the last 20 years, overall skin cancer incidence in the United States has increased 300 percent. While non-melanoma skin cancers are the most common, we’ll focus specifically on melanoma because it’s the scariest — according to the American Cancer Society, one person dies of melanoma every hour. Of the seven most common cancers in the U.S., it's the only one whose incidence is increasing — one Connecticut study found an incidence rate for men 18 times higher in the mid-2000s than in the early ’50s.
Another fun fact: about 86 percent of melanomas can be attributed to exposure to ultraviolet radiation from the sun. Why, then, didn’t the ancient plebeians toiling in the fields all drop dead from malignant skin tumors? Mostly because they dropped dead from a lot of other things first. So yes, cancer was actually very uncommon for the Egyptians, but not because solar UV is no big deal. Life expectancy for the pharaohs only reached 40 to 50 years, and they mostly stayed inside and got fanned with palm fronds. Laborers tended to live maybe 25 to 30 years, so while they likely did receive serious sun exposure, they generally didn’t get old enough for the melanoma to show up. Other reasons for the apparent rarity of skin cancer (and of cancers generally) in antiquity could be the difficulty of detecting tumors in ancient remains, or the increasing carcinogenic factors in our modern environment: pollution, industrialization, depletion of the ozone layer, etc.
There is evidence of bone-penetrating skin cancer from as far back as 2,400 years ago in Incan mummies in Peru, and mentions of skin cancer in the medical literature have increased over the years as both life expectancy and diagnostic skills improved. But what accounts for the fantastically higher incidence rates in the last half-century? The short answer is that the pastiest-skinned among us are baring our bodies at unprecedented levels, and in areas of the world that white skin is ill-equipped to handle.
People with paler skin are 20 times more likely to develop skin cancer than those with darker skin. Additionally, melanoma develops most frequently in those with excessive sun exposure early in life. This explains why the incidence of melanoma in Australians and New Zealanders — whose populations consist largely of transplanted (very pale) northern Europeans — is two to three times higher than in the U.S., where the population is less white and the UV rays less strong.
In other areas of the world, the way we spend leisure time has had a big impact. First of all, we have more of it. The workweek has shortened by a third since 1880, resulting in numerous surplus hours to spend on newly popular outdoor activities. Around 1900 sun exposure was prescribed as a cure for tuberculosis and other illnesses, and tanned skin began to be viewed as healthy, rather than as suggestive of an impoverished lifestyle. Fashion also changed, encouraging people to expose more skin to the sun. Beach holidays boomed in the ’50s, and bikinis took off (and were taken off, in France) in the ’60s. The last straw was the proliferation of indoor tanning centers, which increase your cancer risk even more than the sun. The first one opened in the U.S. in 1978; ten years later there were 18,000 of them.
Analysis of current data suggests that the incidence rate of melanoma is likely to keep increasing for the next two decades at the very least. Attempts to raise sun-exposure awareness haven’t done much, although there’s some sign that in Australia, where one might reasonably be freaked out by the cancer stats, behavior and incidence may have responded slightly to years of high-profile campaigns (Slip! Slop! Slap! Seek! Slide!).
Is skin cancer real? Yes. Can we do anything about it? Doubtful. As any parent of a teenager knows, trying to get people to cover up who don’t want to is pretty pointless. So, barring some global reversal in fashion, skin cancer is just one of those problems the modern world is going to have to learn to deal with.
A rebuttal: it's all your mom's fault
It appears Mr Adams (or his flunkies) were too busy to do much research on this topic. For one thing, chronic sun exposure is protective (if anything) for melanoma. It's not a risk factor for it.
The association between UV exposure and melanoma is quite interesting, but there is agreement in the literature that, while intermittent sun exposure might increase a risk of melanoma, chronic sun exposure helps prevent it (or, at least, doesn't change your risk at all). See here or here for example.
From the first cite:"Analytic epidemiologic studies have shown only modest risks related to sun exposure in melanoma development; three systematic reviews have demonstrated similar estimates for the role of intermittent sun exposure (i.e., odds ratios [ORs] of 1.6 to 1.7). Chronic sun exposure, as observed in those occupationally exposed to sunlight, is either protective or without increased risk for the development of melanoma."
From the second cite:"Chronic exposure, indicated by days of outdoor activity during adolescence and by occupation in recent adult life, was associated with significantly reduced risk."
This leads the cynical among us to realize it must be overprotective mothers and sunscreen lotion that is giving you melanoma. There is certainly no evidence that chronic exposure to UV does. Maybe rich white folk get intermittent exposure because they can afford the beach vacations, and that's why we have this perceived notion that UV causes melanoma when it's really just a risk of white skin and UV itself is actually protective.
So...get your kid outside, throw away his umbrella, and keep him outside.
I acknowledge I didn't draw a distinction between chronic and intermittent sun exposure, and should have. However, to suggest that "overprotective mothers and sunscreen lotion [give] you melanomas" is ridiculous, not to mention irresponsible, and isn't supported by the sources you cite.
Here's what your sources say:
“Intermittent sun exposure is, by definition, sporadic, and is commonly associated with recreational activities, particularly among indoor workers who use weekend or vacation time to be outdoors and whose skin has not adapted to the sun… Intermittent sun exposure seems to be the most important risk factor for melanoma.”
The last point is precisely what was argued in the column: recreational outdoor activities and beach vacations have become more common among countries with paler-skinned populations, causing more people to experience intermittent sun exposure and therefore develop melanoma later in life.
As you rightly note, chronic sun exposure – typically experienced by those occupationally exposed to sunlight – might be without risk or even protective. This is perhaps another reason why melanoma was less common among the Egyptians, and why increased sun exposure has been more harmful lately, when people spend most of their time inside.
But that's my point: the vast majority of adults in countries with high melanoma rates (Europe, the U.S., and Australia) work indoors. For these people, the claimed benefits of chronic sun exposure fact are largely irrelevant. No one can seriously recommend that the way to reduce skin cancer is for everyone to work outdoors. This particularly applies to children, who are legally required to spend most of the day indoors in school. Because of this, any sun exposure they get will be intermittent and therefore dangerous. Lastly, there are numerous studies showing that outdoor workers have vastly greater incidence of non-melanoma skin cancers — UV rays cannot be considered unequivocally safe. In sum, I wouldn’t go telling off any sun-screening mothers just yet if I were you.