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There are many warnings of skin cancer due to exposure to sun, which have turned sunscreen lotions/creams/sprays into a big industry.

Apart from the problem in the product, my question is, are sunscreens needed? Today's average Joe is less exposed to sun (housing, covered vehicles, clothes) than ever before. If the sun was not a problem for thousands of years of human history, and if even today a majority of world population has not even heard about sunscreens, how valid are these health concerns? Or, does it dependent on certain geographic areas (US is somehow in the high-skin-cancer-risk-sunlight area)? Do the problems with the solution(toxicity, suspicious ingredients) outweigh the benefits?

EDIT: I did find two interesting links about possible reasons, and also that melanoma is old

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    It's about more than cancer. Sunburn can be very painful and damaging. I know people who have been hospitalized for it. – DJClayworth Jun 14 '11 at 17:35
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    As a sidenote; the toxicity of a compound can also be dependent upon the exposure route. Nanoparticle TiO2(for example) is the compound used in many sunscreens - the carcinogenicity of the compound is mostly related to its size - as a powder, it tends to accumulate in the alveolar region of the lungs. In a sunscreen, it is bound into solution and as such, the toxicity of the compound is reduced. – Darwy Jun 14 '11 at 17:41
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    @CMR: You've got to consider, though, that prehistoric people might have had much higher melanin levels than we do now. And maybe they sat in caves or under trees for much of the day. And their lifespans were also probably 1/4 what ours are now, so cancer was probably rarely an issue. As for current day, again, many people in Africa/Asia have higher melanin content than Caucasians, so they'll be less affected. It's also a bit of a misnomer to say the Sun is stronger. I know what you mean, but it's the same strength everywhere; some regions just physically get more of it. – erekalper Jun 14 '11 at 18:40
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    Today's man also lives to 72ish instead of 30 or 40. If you don't want to live past 40, then no, it sunscreen is not necessary. The flaw in pretty much all "But we made it 10,000 years without..." arguments is that we live longer now than we have for most of that 10,000 years. – Russell Steen Jun 14 '11 at 21:16
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    CMR, I'm a white New Zealander. 10 000 years ago my ancestors where living in Northern Europe and they didn't have an ozone hole. Today I'm exposed to more sun than they were, and more UV (though the ozone is getting better). Almost everywhere in the world you can see gradients of skin colour, where people living closer to the equator have darker skin. This is good evidence that skin cancer has killed people in the past, and natural selection has favoured dark skin as a result. – david w Jun 14 '11 at 21:58
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Yes. Sunscreen reduces the incidence of skin melanomas. And skin melanomas kill.

Taking those two claims separately:

  • Does sun-screen reduce melanomas?

ABC News reported in December 2010 on some randomly-controlled research, with 1600 people participating, and published in the Journal of Clinical Oncology.

"It provides the first scientific data that shows that sunscreen can be beneficial for melanoma prevention," [...]

[...]

They randomly assigned participants to either receive standard advice on how to use SPF15+ sunblock, or to were given sunblock along with careful instructions and supervision.

After 15 years, there were twice the number of melanomas in the group members who applied sunblock 'now and then', compared to the daily use group.

Original Study: Reduced Melanoma After Regular Sunscreen Use: Randomized Trial Follow-Up, Adèle C. Green, Gail M. Williams, Valerie Logan and Geoffrey M. Strutton, JCO January 20, 2011 vol. 29 no. 3 257-263, doi: 10.1200/JCO.2010.28.7078]

  • Are melanomas serious?

NationMaster.com have mortality statistics for malignant melanomas. The incidence depends on the country, but with 7,420 reported deaths in the USA, it is quite serious (per year? it isn't 100% clear, but that's my assumption.)

It is difficult to compare countries due to different reporting systems, but Australia has only 7% of the population of the USA, but 14% of the malignant melanoma deaths (and a health care system that is at least comparable), suggesting that some countries have a more serious problem with melanoma deaths than others.


Update:

A critical review of the existing evidence for sun-screens has been published.

According to it:

Routine use of sunscreen has been shown to be effective at reducing the development of both [Squamous cell carcinoma] SCC and actinic keratoses, which are known precursors to SCC. However, a statistically significant protective benefit of sunscreen has not been demonstrated against either [basal cell carcinoma] BCC or malignant melanoma.

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    @johanvdw, sure, both of those hypotheses have been suggested. Wikipedia argues "Because of [...] uncertainty, it is difficult to estimate the impact of ozone depletion on melanoma incidence." (en.wikipedia.org/wiki/Ozone_depletion) No doubt, another aspect is sunny weather and outdoor lifestyles that take advantage of that - including a significant beach culture. A thirty-year long campaign promoting sunscreen has seen a drop in some skin cancers, but not melanomas (en.wikipedia.org/wiki/Slip-Slop-Slap). – Oddthinking Jun 15 '11 at 8:37
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    I realize that "double" is a large difference, but the rate never seems to be mentioned in these studies. For instance, if Melanomas are only 1 in 10,000 then doubling gets me 1 in 5,000, which may not be something I want to worry about, as something else is likely to kill me first. – Kibbee Jun 15 '11 at 17:37
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    There has been significant question of late as to the safety of the chemicals in sunscreen. Yes, they are effective at preventing melanoma, but if they are causing some other cancer in return it likely isn't worth it. Of course, this almost certainly varies depending on the formulation. – Muhd May 10 '12 at 22:18
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    @Muhd: as it stands, that comment is just fear mongering. If there is good evidence that sunscreens are carcinogenic, you should link to it in an answer so we can evaluate it. Even if it is true, we need to evaluate the relative risks between the two regimes: it likely causes less fatalities than sun exposure. – Oddthinking May 11 '12 at 0:05
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    @Muhd, no, not any position. But any position that scares people away from important health decisions with the spectre of cancer should be substantiated. The point of comments is to seek/provide clarification to improve an answer, not to offer secret short-cut to enable significant claims without evidence. I do look forward to your answer. – Oddthinking May 11 '12 at 1:47
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There are many alternatives to sunscreen, the most obvious of which you already put in your question: just stay out of direct sunlight during midday. At best sunscreen is convenient.

Furthermore, this well-referenced article argues that there may be health risks to the pervasive use of sunscreens. The article is a bit old, though, so it doesn't take into account the study which Oddthinking provided, but most of it is still relevant.

A summary of the articles' points:

  1. Sunscreen may give people an unwarranted sense of security since not all sunscreens completely block UVA radiation.
  2. Most "chemical" sunscreens (sunscreens that do not use particles as a "physical" reflective barrier) contain benzophenone or its derivatives (oxybenzone is one of them--see this article by the EWG on oxybenzone, it also references a number of studies) which is likely not good for one's health.
  3. Use of sunscreen significantly reduces Vitamin D production, and low blood levels of Vitamin D are associated with increased risk of colon and breast cancer (which have a higher rate of mortality than melanoma)

The article goes on to make some recommendations many of which are good, and some I wouldn't agree with. The most relevant for the discussion at hand (which I agree with) is that you should use sunscreens which use reflective particles to block UV rays (zinc oxide or titanium dioxide). I note that these are not absorbed through the skin the way other sunscreens are.

Another recommendation I agree with (unless you are very fair) is to get moderate doses of sunlight to produce vitamin D and build up a natural resistance to the sun.

  • "Stay out of direct sunlight during midday". So if I (an Australian) want to swim at the beach, what do I do? The sun is equally damaging at 10am or 3pm as it is at midday, so this recommendation doesn't help. What are the other alternatives? You then go on to say that the article recommends a zinc/titanium oxide sunscreen, but that you don't agree with some points in the article (why not?). Do you agree with this specific recommendation? – jozzas May 11 '12 at 4:35
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    "The sun is equally damaging at 10am or 3pm as it is at midday". This is false. The damaging effects of the sun are inversely proportional to the length of your shadow. I would recommend swimming when your shadow is as tall as you are. The vast majority of people do not have to go out in the sun during midday if they don't want to, certainly not to swim. Other alternatives involve wearing clothes and/or using a parasol (if you aren't swimming, or if you are a very talented swimmer). – Muhd May 11 '12 at 5:45
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    To answer your other questions, I don't agree with eating a low fat diet. I believe that saturated fat and (to a lesser extent) monounsaturated fat are some of the best ways to get calories. Avoiding polyunsaturated fats from processed vegetable oils is likely a good idea. I also don't agree with supplementing antioxidants. – Muhd May 11 '12 at 5:57
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    Actually, I'm not sure my advice about the length of your shadow is the best rule of thumb since you are in Austrailia. Probably better to just check the UV index. – Muhd May 11 '12 at 6:03
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    This critical review rejects some of the claims, including vitamin D problems, nanoparticle problems, oxybenzone problems, etc. – Oddthinking Dec 27 '12 at 15:48

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