# Why is skin cancer more prevalent now than in ancient times? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [December 12, 2014, 3:00pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034 "2014-12-12T15:00:37Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [December 22, 2014, 8:46pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/21 "2014-12-22T20:46:00Z")
> [@rob\_bast](#): > > While sunscreen does protect people in the short-term, it gives them a false sense of security. Once the protection runs out, the ingredients of sunscreen actually increase the odds of cancer. Evidence? (Your chart merely shows correlation, not causation.) Powers &8^] ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [December 24, 2014, 12:06pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/22 "2014-12-24T12:06:36Z")
> [@Powers](#): > > Evidence? (Your chart merely shows correlation, not causation.) > Powers &8^] There is no hard evidence of this, but it is a little more than just a “correlation.” Chronically sun-exposed individuals have a neutral or diminished risk for melanoma. Intermittently high-exposed individuals have a somewhat higher risk for melanoma. If it were the sun (UV) causing melanoma, this would not be the case. If it were sunscreen, it would be. If it were getting sunburned that causes melanoma, use of sunscreen would diminish the risk. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [December 24, 2014, 1:12pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/23 "2014-12-24T13:12:39Z")
No one has posted a link to the column yet? [http://www.straightdope.com/columns/read/3192/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times](http://www.straightdope.com/columns/read/3192/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times) ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [December 24, 2014, 7:25pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/24 "2014-12-24T19:25:10Z")
I believe the increase in skin cancer is caused by the increased use of cell phones. I mean, look at the charts. Cell phones cause cancer. That and the increased use of air bags in autos. ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [December 24, 2014, 7:57pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/25 "2014-12-24T19:57:25Z")
[Over a million mummified bodies found in Egypt.](http://www.livescience.com/49144-million-mummy-cemetery-photos.html) I don’t know what most people call that, but I call it **data**! ---
**Author:** ![dropzone](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dropzone/32/7515_2.png) [@dropzone](https://boards.straightdope.com/u/dropzone)\ **Post date:** [December 24, 2014, 7:59pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/26 "2014-12-24T19:59:39Z")
> [@smithsb](#): > > I believe the increase in skin cancer is caused by the increased use of cell phones. I mean, look at the charts. Cell phones cause cancer. That and the increased use of air bags in autos. I thought it was caused by gluten and vaccinations. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [December 25, 2014, 6:27pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/27 "2014-12-25T18:27:57Z")
> [@Chief\_Pedant](#): > > Chronically sun-exposed individuals have a neutral or diminished risk for melanoma. It’s more complicated than this. For instance, chronic sun exposure has been shown to _double_ the risk of getting one type of melanoma ([lentigo maligna melanoma](http://dermatologytimes.modernmedicine.com/dermatology-times/news/modernmedicine/modern-medicine-feature-articles/lentigo-maligna-melanoma-uv-l?page=full)). Add in the heightened risk of other skin cancers (squamous cell carcinoma and basal cell carcinoma) and chronic overexposure to sun (especially without sunscreen protection) is not a good idea (even if you avoid skin cancer, the damage from lots of sun over time prematurely ages you and does not contribute to a flattering appearance). ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [December 25, 2014, 9:29pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/28 "2014-12-25T21:29:12Z")
> [@Chief\_Pedant](#): > > Intermittently high-exposed individuals have a somewhat higher risk for melanoma. > > If it were the sun (UV) causing melanoma, this would not be the case. > If it were sunscreen, it would be. > > If it were getting sunburned that causes melanoma, use of sunscreen would diminish the risk. Not necessarily. The primary culprit is thinking you’re protected when you are not. If you start applying sunscreen and think that will protect you for 6 hours, but it absorbs or sweats off in 30 minutes, and you don’t keep applying more, you’re going to get the sunburn exposure and going to get it more frequently because you are taking more opportunities to get in the sun/more exposure when you do get in the sun. ---
**Author:** ![qazwart](https://avatars.discourse-cdn.com/v4/letter/q/5fc32e/32.png) [@qazwart](https://boards.straightdope.com/u/qazwart)\ **Post date:** [December 25, 2014, 10:10pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/29 "2014-12-25T22:10:54Z")
> [@dropzone](#): > > I thought it was caused by gluten and vaccinations. No. It’s caused by Youtube Kitty Cat videos. The data proves it! ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [December 29, 2014, 12:57pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/30 "2014-12-29T12:57:04Z")
> [@Jackmannii](#): > > It’s more complicated than this. For instance, chronic sun exposure has been shown to _double_ the risk of getting one type of melanoma ([lentigo maligna melanoma](http://dermatologytimes.modernmedicine.com/dermatology-times/news/modernmedicine/modern-medicine-feature-articles/lentigo-maligna-melanoma-uv-l?page=full)). > > Add in the heightened risk of other skin cancers (squamous cell carcinoma and basal cell carcinoma) and chronic overexposure to sun (especially without sunscreen protection) is not a good idea (even if you avoid skin cancer, the damage from lots of sun over time prematurely ages you and does not contribute to a flattering appearance). Of course it’s more complicated. If it weren’t it wouldn’t be controversial. But it is controversial, and Cecil’s column makes the issue appear way more black and white than it is according to the available studies. You cite a “for instance” wrt to UV and lentigo maligna melanoma as if this is one of many examples proving a relationship between UV and melanoma. LMM is pretty much the only example, and in any case this was a limited study done by some derm residents using some generous extrapolations (what state you live in determines your UV exposure) and applies to that very specific subtype of melanoma which accounts for about 15% of all melanomas. (And, I think, there is broad agreement that LMM’s precurson, LM, is UV damage-related.) This study rose to the level of a Poster at a dermatology meeting. That doesn’t mean it’s wrong, but neither is it earth shattering. Finally, you sort of forgot this line from your cite: _"Overall, women and men born in an area of high UV index faced a 37 percent higher risk of LMM and a much lower relative risk of other melanoma subtypes, Dr. Linos says. "_ Dermatologists have it drilled into them as gospel that UV causes melanoma. That’s just plain wrong. UV actinic damage causes skin cancers such as basal and squamous cell, and increases the relative risk of lentigo maligna subtype of melanoma on the order of 1.5 or so. The discussion of lentigo maligna is beyond the scope of this post, but precisely because it is in sun exposed areas and has only a 5% or so transformation to “melanoma,” it sort of sits in its own category. And 85% of melanomas probably have nothing to do with chronic UV exposure. To date the only available literature supports no such contention, since for chronically UV-exposed skin, the effect seems to be protective. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [December 29, 2014, 1:13pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/31 "2014-12-29T13:13:14Z")
> [@Chief\_Pedant](#): > > You cite a “for instance” wrt to UV and lentigo maligna melanoma as if this is one of many examples proving a relationship between UV and melanoma. LMM is pretty much the only example I think that in this post you forgot to emphasize the following: _“There is no doubt that intermittent, intense sun exposure - the kind that frequently leads to sunburn, for example, on tropical vacations - is associated with the development of many melanomas”_ [http://www.skincancer.org/skin-cancer-information/melanoma/melanoma-causes-and-risk-factors/nature-or-nurture-which-is-responsible-for-melanoma](http://www.skincancer.org/skin-cancer-information/melanoma/melanoma-causes-and-risk-factors/nature-or-nurture-which-is-responsible-for-melanoma) Yes - chronic, lower level sun exposure doesn’t pose the same melanoma risk - but it does put people at markedly higher risk of other skin cancers and prematurely ages the skin. Physicians need to do their part to [explode](http://www.mdanderson.org/patient-and-cancer-information/cancer-information/cancer-topics/prevention-and-screening/skin-safety/sunandskincancer.html) [myths](http://www.snopes.com/medical/myths/sunscreen.asp) about skin cancer - including pervasive ones that suggest that skin cancer is not related to sun exposure, and that sunscreen is harmful. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [December 31, 2014, 2:51pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/32 "2014-12-31T14:51:23Z")
> [@Jackmannii](#): > > I think that in this post you forgot to emphasize the following: > > _“There is no doubt that intermittent, intense sun exposure - the kind that frequently leads to sunburn, for example, on tropical vacations - is associated with the development of many melanomas”_ > > [http://www.skincancer.org/skin-cancer-information/melanoma/melanoma-causes-and-risk-factors/nature-or-nurture-which-is-responsible-for-melanoma](http://www.skincancer.org/skin-cancer-information/melanoma/melanoma-causes-and-risk-factors/nature-or-nurture-which-is-responsible-for-melanoma) > > Yes - chronic, lower level sun exposure doesn’t pose the same melanoma risk - but it does put people at markedly higher risk of other skin cancers and prematurely ages the skin. > > Physicians need to do their part to [explode](http://www.mdanderson.org/patient-and-cancer-information/cancer-information/cancer-topics/prevention-and-screening/skin-safety/sunandskincancer.html) [myths](http://www.snopes.com/medical/myths/sunscreen.asp) about skin cancer - including pervasive ones that suggest that skin cancer is not related to sun exposure, and that sunscreen is harmful. I have already presented cites showing some data that intermittent exposure to sun is associated with a higher risk of melanoma. But you are missing the whole point! It’s not a question of whether or not the intermittently exposed have a higher incidence (and fwiw, the notion that those are the folks who got sunburned is an assumption, since the chronically exposed could just as easily get burned along the way). It’s a question of causality, not simply concluding post hoc ergo propter hoc. If UV caused melanomas, we’d see a high incidence of melanoma in people exposed to a lot of UV. If sun screen causes melanoma, we’d see a high incidence of melanoma in people using a lot of sun screen. If UV increases LMM and is protective against the 85% of other melanomas, what kind of evidence is that sun exposure is net harmful? I have no idea what causes melanoma. But there is no more evidence that it is the sun’s UV than that it is some other factor such as sun screen. And the fact that chronic exposure to UV is protective should make the knee-jerk association with UV fail the sniff test for an assumption of causation. Beyond that, instead of reading a Snopes opinion about an article, why not read the original publication? It’s [here](http://onlinelibrary.wiley.com/doi/10.1111/joim.12251/pdf) and it basically says women who don’t get as much sun have excess mortality. “The mortality rate amongst avoiders of sun exposure was approximately twofold higher compared with the highest sun exposure group, resulting in excess mortality with a population attributable risk of 3%.” The irony, of course, is that the reason they had the 20-year data to look at in the first place was because of the sun/melanoma panic leading to the MISS study. Now that’s irony! Physicians should be all about exploding myths and relaying instead what the data show. For melanoma it’s a fascinating nest and I recommend sticking to original literature since the Sun=Danger myth is so friggingly and pervasively ingrained that nearly every lay author and frankly a great many medical authors take it as a default position. Even worse, the available data show that avoiding the sun may be a greater risk than not avoiding it, melanoma be damned. In the old days a Cecil column would have tackled and analyzed the fine points. This one doesn’t. It just spouts the superficial assumptions. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [December 31, 2014, 3:05pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/33 "2014-12-31T15:05:15Z")
> [@Jackmannii](#): > > Physicians need to do their part to [explode](http://www.mdanderson.org/patient-and-cancer-information/cancer-information/cancer-topics/prevention-and-screening/skin-safety/sunandskincancer.html) [myths](http://www.snopes.com/medical/myths/sunscreen.asp) about skin cancer - including pervasive ones that suggest that skin cancer is not related to sun exposure, and that sunscreen is harmful. One other quick point: Be careful not to conflate “melanoma” with “skin cancer.” Sure; most melanomas start in the skin. But no reasonable student of the topic thinks ordinary skin cancers (basal and squamous, e.g.) are unrelated to UV exposure. Neither are they in the same league as melanoma for lethality. At issue for me are two points: 1. Is being in the sun overall beneficial or harmful? 2. Is UV exposure the cause of melanoma? See above. If instead, you just make a point that “sun causes skin cancer,” you have not given a patient enough information to decide whether or not to avoid the sun. In fact, all you’ve done is leave an impression that one should stay out of the sun. That impression has been left with many of the masses, who are slathering up with sunscreen or staying inside. Should the turn to the Straight Dope column on “skin cancer” they aren’t going to leave with the straight dope, and will instead be just as ignorant about the data as when they started. ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [December 31, 2014, 6:50pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/34 "2014-12-31T18:50:28Z")
Another aspect to changing rates that Cecil only hints at - rapid (from an evolutionary perspective) changes in where populations live. Skin pigmentation adaptations to irradiance levels take many generations but we have moved around lots over the past centuries with some dark skinned people living in low intensity areas and paler people living in higher irradiance locations. IOW, there is a geographic and lifestyle _mismatch_ between location skin pigment characteristics. See [here](http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1056&context=anthropologyfacpub) (pdf) for a discussion. > [@](#): > > Jablonski and Chaplin (2010:2) acknowledge the value > of dark skin in protecting against skin cancer in the following: > “Skin cancers are mostly a consequence of modern > human migrations and resulting mismatches between > skin pigmentation and geography or lifestyle.” > We agree with their mismatch hypothesis. The key > point they make is that dark skin protects against skin cancers. > To understand the value of dark skin, we can think of > no better natural experiment (Beall and Steegman, 2000; p > 201) than to examine skin cancer rates of those whose ancestral > homelands were in low UV environments but who > currently grew up and live in higher UV environments. If > dark skin coloration is a protective response to skin cancer > then light skinned individuals should show greater skin > cancer rates than their dark-skinned ancestors who continue > to live in their aboriginal homelands. > Skin cancer incidence rates for darkly pigmented populations > living at low latitudes are few. This is due in > part to the lower incidence rates in these groups relative > to lightly pigmented populations—since the latter have > higher mortality rates from skin cancer, research is focused > on combating this issue … > > … In addition to skin cancer incidence rates among populations > living in place, populations that have migrated > from their ancestral latitude to more equatorial climates > provide a natural experiment with which to judge the differential > effect of UVR on lightly and darkly pigmented > groups. It is widely accepted that lightly pigmented > groups living at low latitudes will suffer from skin cancer > at a higher rate than populations with darker pigmentation > in the same region (e.g., Lomas et al., 2012). Beall > and Steegman (2000) demonstrated this relationship in a > sample of African-Americans and whites living in Texas, > arguing that this natural experiment supported skin cancer > as a selective agent in skin pigmentation. This discrepancy > is also illustrated by CMM incidence in Maori and > non-Maori subjects living in New Zealand. The distance > that sun-sensitive populations living near the equator > have traveled from their ancestral latitude is substantial > and likely would not have occurred during prehistory, > but contemporary skin cancer incidence demonstrates the > clear adaptive benefit of dark skin pigmentation against > UVR. Skin cancer has been a major health issue in these > groups and the data support an increase in skin cancer > incidence over time (e.g., Birch-Johansen et al., 2010). Increases > in skin cancer incidence are also likely influenced > by changing attitudes toward sun-seeking behavior and > atmospheric depletion of ozone (Buller et al., 2011; Lemus-Deschamps > and Makin, 2012). > The relationship between UVR and skin cancer may > not be as clear as was once believed. CMM risk may also > be influenced by the presence of skin damaged by scarring, > tattoos, or burns (Camain et al., 1972; Chadwick et > al., 2012). … ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [December 31, 2014, 8:52pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/35 "2014-12-31T20:52:37Z")
> [@Chief\_Pedant](#): > > the available data show that avoiding the sun may be a greater risk than not avoiding it, melanoma be damned. Talk about missing the point. It’s not a matter of “stay indoors, don’t get exercise and have low vitamin D levels” versus “enjoy all the sun and tanning bed exposure you want”. Based on the evidence we have, there’s ample reason to employ _moderation_. > [@](#): > > If instead, you just make a point that “sun causes skin cancer,” you have not given a patient enough information to decide whether or not to avoid the sun. We have excellent evidence that skin cancer causation is related to degree of sun exposure. The epidemiology is at least as good as that showing smoking is related to various cancers. Any physician who tells or implies to patients that using sunscreen and moderating their sun exposure is likely to have an equivalent impact on their health as getting chronically tanned/sunburned is doing a severe disservice to them. It is clear that skin cancer risk overall is tied to lots of sun exposure. This is not a he-said-she-said matter (remember, the skin cancers that are non-controversially tied to sun exposure (squamous cell and basal cell carcinoma) are way way more common than melanoma). There’s a lot of crankery out there that suggests sunscreen is somehow toxic and part of a plot by Big Pharma (or at least Big Coppertone) to _cause_ cancer. It has been aided and abetted (sometimes unwittingly) by otherwise knowledgeable physicians (here’s looking at _you_, Bernard Ackerman). Physicians ought to be about opposing crankery with good evidence, not enabling dangerous behavior. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [December 31, 2014, 9:03pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/36 "2014-12-31T21:03:29Z")
Regarding hype about sunscreen harm - it runs the gamut from “respectable” sources like [Dr. Oz](http://www.doctoroz.com/article/your-sunscreen-might-be-poisoning-you), all the way into the deeply crazy ([Natural News](http://www.naturalnews.com/045676_sunscreen_cancer_vitamin_D.html)). For a science-based look at benefits and potential risks, try (surprise!) [Science-Based Medicine](http://www.sciencebasedmedicine.org/the-great-sunscreen-cover-up/). ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [December 31, 2014, 10:50pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/37 "2014-12-31T22:50:20Z")
I am not trying to persuade you that sunscreen is harmful. I am pointing out that there is no more data that UV causes melanoma than that sunscreen does (wrt the 85% of non-LMM melanoma). I’m not sure Dr Oz is a respectable source, but your mileage may vary. Feel free to post any scientific cite related to sun exposure and melanoma if you want to help me understand the data better. I prefer the original rather than a lay distillation. And once again, if you conflate “melanoma” and “skin cancer” you are going to get very confused about UV and melanoma, for the reasons I mention above. And as a last point, did you have a cite showing exposure to the sun is net dangerous? Something to offset the MISS study I set forth above? If you don’t, in your opinion what sort of behaviour should physicians be encouraging based on evidence regarding sun exposure? ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [December 31, 2014, 10:56pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/38 "2014-12-31T22:56:40Z")
> [@Chief\_Pedant](#): > > I am not trying to persuade you that sunscreen is harmful. Then you need to stop making comments like this: > [@Chief Pedant](#): > > I have no idea what causes melanoma. But there is no more evidence that it is the sun’s UV than that it is some other factor such as sun screen There is _zero_ evidence that sunscreen causes melanoma or any other cancer. On the other hand, there is evidence that sun exposure (intermittent, strong) increases risk of melanoma in general, plus the previously described link between lentigo maligna melanoma and sun exposure. This should not be so difficult to understand. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [January 1, 2015, 12:56pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/39 "2015-01-01T12:56:14Z")
> [@Chief\_Pedant](#): > > I have already presented cites showing some data that intermittent exposure to sun is associated with a higher risk of melanoma. > > But you are missing the whole point! > > It’s not a question of whether or not the intermittently exposed have a higher incidence (and fwiw, the notion that those are the folks who got sunburned is an assumption, since the chronically exposed could just as easily get burned along the way). > > It’s a question of causality, not simply concluding post hoc ergo propter hoc. > > If UV caused melanomas, we’d see a high incidence of melanoma in people exposed to a lot of UV. If sun screen causes melanoma, we’d see a high incidence of melanoma in people using a lot of sun screen. If UV increases LMM and is protective against the 85% of other melanomas, what kind of evidence is that sun exposure is net harmful? > > I have no idea what causes melanoma. But there is no more evidence that it is the sun’s UV than that it is some other factor such as sun screen. And the fact that chronic exposure to UV is protective should make the knee-jerk association with UV fail the sniff test for an assumption of causation. Melanoma (including the 85% you are stressing) is caused by sun damage from UV. Melanin is protective to melanoma. Melanin is activated by chronic sun exposure. Intermittent sun exposure leaves melanin lower, leaving greater risk for the times that the light skinned are exposed. Sun screen blocks UV. However, sun screen needs to be applied thoroughly to cover the skin, and it has problems with (a) washing off, (b) soaking into the skin, and (c) the chemicals being physically changed by the UV to make them cease working. All three problems mean that, regardless of the SPF, sun screen needs to be reapplied frequently, at least once an hour, and needs to be applied liberally. [This page](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1128750/pdf/176.pdf) discussing application says that the standard test amount is 2 mg/cm[sup]2[/sup], but many people only apply 0.5 to 1.3 mg/cm[sup]2[/sup]. That means they get less protection than the people rating the SPF expect. [This page](http://www.cancer.org/cancer/cancercauses/sunanduvexposure/skincancerpreventionandearlydetection/skin-cancer-prevention-and-early-detection-u-v-protection) says use 1 oz for your legs, arms, neck, and face. That’s about a palmful. I’m not sure reading that but I think it means 1 oz for each of those, as opposed to 1 oz total. Light-skinned people with chronic sun exposure get tanned, which protects them better than light-skinned people with intermittent exposure. Tanning also protects against sunburn. You seem to be saying that the connection between protection from sunburn associated with melanin and the protection from melanoma associated with melanin is just a coincidence, and the real culprit is sun screen use. Another confounding factor is that UV is divided into UVA and UVB by wavelength. Roughly speaking, [UVA is skin damaging UV and UVB is burning UV](http://www.sciencebasedmedicine.org/the-great-sunscreen-cover-up/). Traditionally, chemical sun screens have only been concerned with stopping the burn, or blocking UVB. Mineral sunscreens (zinc oxide, titanium dioxide) block both. The FDA is [proposing new guidelines](http://www.uspharmacist.com/content/t/dermatology/c/10106/) to label protection for both UVB and UVA. If sun screens have largely been concerned with only blocking UVB and not blocking UVA, but UVA is also cancer causing, then there is risk for cancer even when using sun screens. This could lead to people getting more exposure to the sun but thinking they are protected during the intermittent exposure, whereas those with chronic exposure get the additional protection of melanin. Thus, the risk pattern to melanoma that you cite with regards to the intermittent sun exposure being riskier than chronic exposure to the sun. > [@](#): > > Beyond that, instead of reading a Snopes opinion about an article, why not read the original publication? It’s [here](http://onlinelibrary.wiley.com/doi/10.1111/joim.12251/pdf) and it basically says women who don’t get as much sun have excess mortality. > “The mortality rate amongst avoiders of sun exposure was approximately twofold higher compared with the highest sun exposure group, resulting in excess mortality with a population attributable risk of 3%.” > > The irony, of course, is that the reason they had the 20-year data to look at in the first place was because of the sun/melanoma panic leading to the MISS study. Now that’s irony! > > Physicians should be all about exploding myths and relaying instead what the data show. For melanoma it’s a fascinating nest and I recommend sticking to original literature since the Sun=Danger myth is so friggingly and pervasively ingrained that nearly every lay author and frankly a great many medical authors take it as a default position. > > Even worse, the available data show that avoiding the sun may be a greater risk than not avoiding it, melanoma be damned. I read the study from your cite. That study is examining the role of vitamin D deficiency in mortality. They state: > [@](#): > > Ultraviolet (UV) radiation from the sun is known to heighten the risk of developing malignant melanoma (MM) of the skin. This condition is primarily responsible for increased mortality due to UV radiation exposure. The risk of MM varies widely amongst people of different skin colour, depending on the type of melanin in their skin. MM is most common amongst Northern Europeans with pale skin and is rare amongst Africans with very dark skin [1]. Individuals with red hair or a tendency to develop freckles are at increased risk of developing MM. The highest risk has been found amongst those of European ancestry living in Northern Australia [1]. This has been the basis for considering UV radiation as the major cause of MM. Programmes for avoiding UV radiation are widely implemented in societies in which a large proportion of the population is descended from Europeans [2]. Nowhere in the paper do they refute that claim. They also state: > [@](#): > > Sun exposure increases the risk of MM mainly through episodic sunburn or frequent use of tanning beds in individuals with unprotected fair skin. The incidence of MM represents the greatest increase of all cancers affecting women at lower age than men. The disease is fatal in approximately 20% of patients with MM. Basal cell carcinoma and squamous cell carcinoma often affect older individuals and are mostly associated with cumulative exposure to UV light. The incidences of both these types of tumour are increasing. I’m not sure how that is supposed to support your position that UV does not cause MM. Another quote from the paper: > [@](#): > > Low vitamin D concentrations have also been linked to thicker, more aggressive melanomas with shorter survival times [9]. Thus, opposing mechanisms may act with regard to MM and sunlight exposure. In other words, very low sun exposure is linked to more aggressive melanomas with shorter survival times. Explain again how that is the fault of sun screen. I will point out that looks somewhat like a contradiction: low sun equals melanoma, but intermittent sun equals melanoma. However, that is balancing the risks of low vitamin D against the risks of UV exposure. They point out the characteristics of the melanomas for the two conditions tend to differ. > [@Chief\_Pedant](#): > > At issue for me are two points: > > 1. Is being in the sun overall beneficial or harmful? > 2. Is UV exposure the cause of melanoma? From the [Dr Oz page](http://www.doctoroz.com/article/your-sunscreen-might-be-poisoning-you) decrying the chemicals in sun screen: > [@](#): > > UV light causes skin cancer and prematurely ages the skin, and so it’s very important to protect our skin with sunscreen. We don’t want to block sunshine completely – about 20 minutes each day is good for us – it boosts our vitamin D and improves our mood. Beyond 20 minutes, however, and our immune system suffers. We either need to spend the rest of the day inside or protect our skin with sunscreen. Even that page says 20 minutes a day is sufficient sunlight, and more is detrimental. 1. Some sun is good, a lot of sun is bad. 2. UV causes melanoma, but the protection of melanin means intermittent exposure leads to more cases than chronic exposure, and sun screen has not been great at limiting exposure to all bands of UV, so people think they are protected because they are protected from burns, but are getting more exposure via UVA so are at greater risk for melanoma. ---
**Author:** ![Chief\_Pedant](https://avatars.discourse-cdn.com/v4/letter/c/a6a055/32.png) [@Chief\_Pedant](https://boards.straightdope.com/u/Chief_Pedant)\ **Post date:** [January 1, 2015, 1:25pm UTC](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034/40 "2015-01-01T13:25:21Z")
> [@Irishman](#): > > Melanoma (including the 85% you are stressing) is caused by sun damage from UV. Read the articles in Post 13 and let me know how you came to this conclusion based on available literature. As to overall mortality, you are really confused. The Swedish study from the MISS data looked at overall mortality, and the raw data is that more sun exposure diminishes overall mortality, even taking into account any increase in mortality from malignant melanoma. While I appreciate you taking time to link out to various consumer oriented cites, I’m not interested in them. If you have some literature cites you want to parse out, I’ll try to take a look at them for you. Your notion that people with chronic exposure get tanned, and that this is what protects them, is a postulate. It may or may not be right, but there is no direct support for it. What has happened with the UV hoopla is the broad impression by the public that one should never get tanned, and avoid the effects of UV at all costs, with heavy application of sunblock and staying out of the sun where possible. This is unsupported as a route to avoid melanoma or reduce your overall mortality. To summarize: the available literature shows chronic sun exposure will reduce your mortality and diminish your overall chance of getting melanoma. As with any literature, this may be wrong. But it is the current state of the science. [Previous page](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034.md?page=1) [Next page](https://boards.straightdope.com/t/why-is-skin-cancer-more-prevalent-now-than-in-ancient-times/707034.md?page=3)