4 things you didn't know about sunscreen

Good, bad, ugly.jpg

Starting next year, sunscreen—and the way its marketed—will change. This is good news. The changes correct some rather glaring examples of consumer misinformation. And it's also important news ... at least, from the perspective of this redhead.

New Food and Drug Administration regulations mean that, by the summer of 2012, there will be no such thing as "waterproof" sunscreen. That's because, frankly, there already wasn't such a thing. A sunscreen might be more water resistant than a competitor. But you can't assume that one application of the "waterproof" stuff will stay with you through hours of pool time. Next year, sunscreen bottles will be honest about that fact, and they'll tell you how long you can expect water resistance to last.

The other big change: What the sunscreen protects you from. Under the new regulations, only broad-spectrum sunscreens—the kind that protect you from both the UVA and UVB wavelengths of solar radiation—with SPF values of 15 and higher, can claim to prevent skin cancer. Anything else must tell you that it's just for preventing sunburn.

These changes bring marketing into line with evidence, which always a good thing where public health is concerned. But, to me, they also bring up an important issue that remains unresolved. More and more Americans are using sunscreen. But that's not the same thing as more Americans understanding sunscreen. Information is important, and packaging can only be expected to do so much. With that in mind, I present this short guide to the seldom-discussed details behind an everyday product.

1) There's not absolute proof that sunscreen prevents cancer. You should still use it, anyway.

Here's the funny thing about cancer: It doesn't happen instantly. Instead, you get exposed to a carcinogen and, maybe (depending on how much carcinogen you were exposed to, how long you were exposed to it for, and other factors like genetics) you might develop a cancer 30 or 40 years later. By then, it's very difficult to determine cause and effect, both for the carcinogens themselves AND for things that prevent cancers from happening. This is a fact that's easy to forget. But it rears its head every time we try to talk about cancer—whether it's skin cancer caused by the sun, fears about brain cancers caused by cell phones, or the cancers that follow a nuclear power plant meltdown.

Here's the funny thing about sunscreen: Americans haven't been using it for very long. "The connection between sun exposure and skin cancer wasn't even talked much about at all just 30 years ago," says Christopher Arpey, M.D., professor of dermatology at the Mayo Clinic. "To say, 'you did this when you were 20 and now here you are 40 years later, and this is why you've got skin cancer or don't have it,' that's hard to do. It takes a really long time to build that evidence."

We do know that using sunscreen prevents sunburns and premature aging of the skin, but those are different things from cancer. The risks and the evidence available also depend on the type of cancer. Reynold Tan, Ph.D., is an interdisciplinary scientist with the FDA's Office of Nonprescription Products/Division of Nonprescription Regulation. He says there's stronger evidence supporting sun exposure as a cause of, and sunscreen use as a preventative of squamous cell carcinoma—a specific type of skin cancer that's been strongly linked to repeated, chronic skin damage from solar radiation. On the other hand, you have something like melanoma, which is known to have a strong genetic component, and there the outlook is still a lot more hazy.

But, despite the uncertainty here, sunscreen is still important. While we don't have all the evidence yet, the weight of evidence that does exist supports sunscreen use as a way to prevent skin cancer. "We know that regular sunscreen users develop fewer precancers over time," Dr. Arpey says. Even if sun exposure isn't the only cause of skin cancer, there's a good chance that it's an important cause. There's a lot we don't know, but we can still act on the information we do have.

2) SPF isn't a percentage, and it is kind of relative.

To understand what Sun Protection Factor really means, you have to know what happens in the studies that determine which sunscreen gets awarded what SPF value. These experiments are done with people, volunteers who have sunscreen applied to some parts of their bodies, but not to others. Then, they're exposed to UV light, and researchers measure how much longer it took the protected parts to burn compared to the unprotected parts.

SPF 30 just means that it took a dose of UV 30x larger to induce a sunburn on the protected skin, compared to unprotected. But that's not the same thing as saying that, if you put on some SPF 30, you can stay out in the sun 30x longer.

"It's a dose," Tan says. "And dose is intensity and time. So, depending on the intensity of the sun on that particular day, it's not necessarily 30x longer. Also the 30x higher dose is measured in a laboratory. When you're outside, you're sweating and you're rubbing it off on your clothes."

One downside to the new regulations is that they'll make this even more confusing. That's because the experiment I just told you about, and the SPF rating that comes out of it, really only applies to UVB wavelengths—the stuff that's most associated with causing sunburns. It says nothing about protection against UVA, which is most associated with causing cancer.

Beginning next year, companies will have a big incentive to get their products certified as "broad spectrum," protective against UVA and UVB. To do that, the FDA runs a different test, putting sunscreen on a slide and examining it with a spectrophotometer. By observing which wavelengths of light get absorbed, and which don't, the researchers can see how well the sunscreen does at protecting a person from UVA.

The SPF ratings on "Broad Spectrum" certified sunscreens will take this into account, Tan says. But those ratings will be relative only to other sunscreens. "Broad Spectrum SPF 30, compared to Broad Spectrum SPF 15, provides higher UVA and UVB protection," he says. "But you can't really say it's double the UVA protection. The only way to objectively measure that would be to look at absorption curves themselves and see how well a product works against each individual UVA and UVB wavelengths, but that's not very helpful for consumers."

3) You don't use enough sunscreen

At least, not enough to assume that the SPF rating on the bottle applies to you. Remember the experiment that determines a sunscreen's SPF rating? In those studies, sunscreen is slathered on thick—2 milligrams per centimeter squared, according to Reynold Tan. In real life, he says, people use something like 1/2 to 1/4 as much.

This isn't necessarily a problem, Dr. Arpey says. He's more worried about compliance—whether people are using sunscreen at all—than whether they're following manufacturer's instructions to the letter. If you're more likely to use sunscreen when you put on less, then put on less. But just remember that, when you do, your sunblock isn't operating at the advertised strength.

4) Sunscreen absorbs solar radiation.

Well, anyway, some sunscreens do. There are really two types. You can get sunscreen that works by simply being a physical barrier, reflecting the light away from you. That's how products with zinc oxide or titanium dioxide as the active ingredients work.

Everything else involves large molecules that mimic natural melanin by absorbing energy from the light, rather than blocking it. And that brings up another question: What do the molecules of active ingredient in those types of sunblock do with all that energy? The answer involves atoms and electrons.

You know that electrons go around the nucleus of an atom. The regions of space those electrons move through are called "orbitals." It's helpful—although not wholly accurate—to imagine them as the Sun, encircled by the orbits of planets. Unlike planets, though, electrons can move from one orbital to another, when they absorb the right amount of energy. Imagine Earth bouncing up suddenly from its orbit to that of Mars. That's essentially what happens with the electrons in the atoms of your sunscreen's active ingredient are hit with solar radiation.

"Electrons dispel the energy by moving to a higher orbital," Tan says. "Then they come back to stable lower orbitals." This process happens quickly, he says, over and over and over during the time you're wearing sunscreen. And it gives the radiation energy from the sun something to do besides penetrate your skin.

Image: Beer, cigarettes and sun block: Roskilde Festival 2009 essentials., a Creative Commons Attribution (2.0) image from wouterkiel's photostream


  1. Maggie, I think I once heard that sunscreen expires (like milk eventually), but I don’t know if it’s true. I typically use sunscreen in the summer, then, it sits there on the shelf over the winter. I’ve never seen a bottle with an expiration date (I assume they won’t do it until they have to). Do sunscreens expire? I figure you might know. (Great article!)

      1. all of my sunscreens have expiration dates

        Moist make-up (as opposed to powders) should generally be dumped after six months. Unless you’re trying to flesh out your zombie look with styes and carbuncles. If you’re using sunscreen seasonally, you should consider dumping it at the end of the season and buying fresh every year.

  2. Interesting. Definitely somethings I did not know. I’ll be rereading the backs of my SPF lotion bottles.

  3. The ironic picture of sunscreen, beer and cigarettes. Really, why bother putting it on at all? Slather some coconut oil and and bake while you smoke and drink.

    In other news, sunburns are my least favorite thing, having had one so bad a few years ago that the only relief I could find from the subsequent itching involved cold concrete and ice baths.

    Great story on sunscreen btw, I didn’t know some of that.

      1. My best advice is barely-warm tub of water with a lot of baking soda. Soak until the water is starting to be too cool for comfort, which should take several minutes, so bring a book.

    1. Your story is exactly why a person who smokes and drinks would bother with sunscreen. Sure, cancer may kill me later but sunburns suck NOW. Nothing like painful feedback to encourage sunscreen use.

    2. I have seen plain, non-fat yogurt —slathered on, wait for 15 minutes (or more), then rinse— take a sunburn to a tan, with no pain. It’s amazing. It has to be plain, non-fat. Others will make the pain worse.

      I’ma gonna try the apple cider vinegar thing that Trixie suggests, if I get a burn this year. Never heard that one before.

      But I know personally that the yogurt trick works.

  4. It seems to me that the best answer is just to avoid the evil day star as much as possible. I’d much rather moderate my exposure than try to sort through complex and incomplete data about how products may or may not protect me from the dangers of the sun.

    1. Sunlight does your body some good, too, mind you. No amount of vitamin d supplementation through diet can counteract not getting enough sunlight exposure to help your body make use of it, for example. We’re all designed to be out in the sunlight for at least part of every day.

      1. Sure, we all need sunlight. Like most other things, though, moderation is important. I’d rather expose myself to a moderate amount of sun than to get tons of it and try to guess which products will and won’t protect me.

    2. I’m with you .100%. The sheer complexity of sorting through sunscreens, running molecular comparisons, and reading the directions on the back are exhausting. Not to mention The Death Star, which indeed is an evil, evil place.

  5. Great information Maggie.
    One question, what kind of energy do the electrons release when dropping down again? Is this energy released as heat or some other kind of radiation? (basically the question is, at what frequency is the energy that is released?)

    1. Typically sunscreens absorb light from 380nm-200nm and beyond they undergo non-radiative decay through heat, however there are some that can weakly fluoresce. If you get some sunscreen on your clothes and go moonlight bowling you’d glow a bit blue. Especially on your clothes.

      Some sunscreens are triplet sensitizers that can actually generate singlet oxygen (highly reactive oxygen species that essentially destroy any non-aromatic unsaturated hydrocarbon molecule and DNA). This is a double edge sword as singlet oxygen can actually cause cancer as well, however the permeability of sunscreen and singlet oxygen through the skin is very debatable as scientists haven’t studied it (to my knowledge) extensively.

      Full disclosure I’m getting my PhD in Photochemistry.

      1. Oh, rats. All I get is some flourescence and heat? Here I was all set to get Henna-style body doodles with a circuit-drawing pen and charge my phone while I laid on the beach….

  6. I certainly agree that government regulation on advertising is helpful for the cause of public health. However, I noticed that this news gathered a surprising number of comments on CNN regarding government interference with personal rights. The issues of personal rights and corporations’ rights (which in this case is the right to make unsupported advertising claims) are clearly distinct. As such, it is frustrating to see people champion corporations’ rights as their own.

    Reading your thoughtful opinions regarding science and public policy is refreshing.

  7. “4 things you didn’t know about sunscreen” …do i get a cookie if i did indeed know those things? (plus at least two more not widely known) i demand for sake of scientific formality that error estimates be placed on any future wild use of the public “you”, e.g.: “you +/- 0.13%” thankewverrrymuch.

  8. This is the most helpful thing I have read on sunscreen ever, and I have actively looked for good information on what kinds of sunscreens are best to buy.

    I’ve been using sunscreen since I was a kid (I’m not fond of the sun anyway, but I really don’t want sun damage either) and I often wonder how much good what I have is doing or whether I’m better off with a physical block, whether the higher SPF is worth it because I spend most of my day indoors and it has probably worn off by the time I leave but it’s hard to find good straightforward information that isn’t more or less just advertising.

    Hats and clothing with sleeves help too. Where I live the sun is overwhelming, you really need some kind of sunscreen even if you don’t spend a lot of time outdoors.

  9. 5. Transparent sunscreens were one of the first wide-scale deployments of nanotechnology in a consumer product. They’re transparent because the TiO2 or ZnO particles are smaller than the wavelength of visible light, and so don’t scatter it. Scattering of visible light by large TiO2 particles is the reason that white paint is white, and also why ‘old fashioned’ sunscreen looks a lot like white paint. Nano-sized TiO2 and ZnO particles still absorb UV like their bigger cousins, so badda bing badda boom transparent sunscreen.

    Do smaller particles interact differently with our skin? We’re not really sure. Small particles means a higher surface area (important for chemical reactions) and also more chance of squeezing through protective barriers in the skin. The first link I could find on Google: http://www.nanowerk.com/spotlight/spotid=714.php

    The jury’s out but it’s one of those things that deserves far more testing before such wide-scale deployment.

  10. I’d rather have melodrama than melanoma.

    By your whitey thighs I can tell you could use some Vitamin D.

  11. Not one mention of nanoparticles used now for almost all sunscreens? Nanoparticles can enter the blood stream quite easily through the skin. Also, titanium dioxide, the main ingredient in most sunscreens is a known carcinogen. It’s in a lot of makeup now as well. Added SPF protection was the “now with zero transfat” of 10 years ago. And who knows ago zinc oxide when it has been reduced to nano size. America, the human guinea pig!

    Effectively, when we use sunscreen we are turning ourselves into the tinman from oz (the movie version tinman, with the metal body paint). You used to be able to see the sunscreen as you slathered it on. But because of the nanoparticaling of the metals, it’s more translucent and people like that better. I worry about the aerosol version of sunscreen, the one I inhale as the overprotective mother sprays her childs entire face and body with.

      1. Which could have been prevented by a balanced diet. Vit D is not hard to come by in foods or supplements.

        1. Vitamin D (D2) may be present in various supplements and foods but pro-Vitamin D (what your body makes with sunlight) is not. And it’s the pro-Vitamin D that is highly anti-carcinogenic. Vitamin D in your pill or your milk may prevent rickets but there’s no solid evidence of it helping with cancer when in supplement form. Pro-Vitamin D (which your body can convert to Vitamin D) is just not available from any source other than sunlight, period.

    1. “And who knows ago zinc oxide when it has been reduced to nano size.”

      Well, YOU don’t, so maybe lay off the unfounded paranoia.

      Did you know that there’s no proof that reading this comment doesn’t give you cancer? WE JUST DON’T KNOW!

    2. You may want to do some research before you go freaking out. Here’s a link to a paper on the topic. http://www.ncbi.nlm.nih.gov/pubmed/20354643

      Notice the first sentence of the abstract is “Based on the current weight of evidence of all available data, the risk for humans from the use of nano-structured titanium dioxide (TiO(2)) or zinc oxide (ZnO) currently used in cosmetic preparations or sunscreens is considered negligible.”

      Sort of like how the odds of tea giving us cancer is negligable. Or coffee. Or pickled vegetables.

      1. Personally I’m not worried that titanium dioxide is a hazard to users of sunscreen/cosmetics. But the production of TiO2 has discharged dioxins into the local environment of the chemical plants in the past. in the US DuPont has had to pay remediation costs. Here’s an inadequate but scientific source: http://pubs.rsc.org/en/Content/Database/HAZ2206001777

        I don’t know whether they’ve changed their production methods, but I avoid buying TiO2-based products for now.

  12. It should be noted: The Environmental Working Group (EWG) really pushed for changes to sunscreen regulations. They also publish a list of sunscreens that actually work and don’t contain harmful chemicals.

    They are also not very happy with the final rules put in place and feel they are only a slight improvement of the previous rules.

    And everyone knows menthols have more vitamin C and so are better for you than regular cigarettes.

  13. Although I agree that too much sun exposure isn’t good for the skin, I’m dubious about repeatedly slathering my body with chemicals that react with sunlight and then get absorbed into my body through the skin. The long terms of effect of this?….

  14. I’m less worried about cancer. I’m probably going to die from cancer if I don’t have a heart attack. This is because I worked with high gloss enamel paints for years and I have an arrhythmia. So, I exercise, don’t smoke, try to drink lightly and whatnot but the truth is I’m probably going to die of cancer or a heart attack (if I don’t get murdered or die in a car accident of course)

  15. No one’s mentioned the clear nominative determinism here yet? Reynold Tan, Ph.D.? Dr Tan? Anyone?

  16. “You ever read the ingredients in sunblock? I’ve never seen those words anywhere!
    You don’t even know what you’re putting on your face, do you? ‘Oh no, the sun’s out, ahh’ – it could be zebra cum, you don’t know!”

  17. Question, I always thought that sunscreen absorbed the energy by making your skin a color that’s invisible to us on the spectrum (like bee purple). I can’t remember if someone told me this, or if I made up the explanation myself. Any truth to this?

  18. Most sunscreen is also tested by putting it on so thick the person looks like they have been slimed in it. Further, almost all sunscreens have ingredients that aren’t even deemed safe by the FDA. This website has the down low on just about every brand out there. You’ll be shocked…http://breakingnews.ewg.org/2011sunscreen/

    Look at this kid’s sunscreen for example, insane what is in it. http://breakingnews.ewg.org/2011sunscreen/about-the-sunscreens/381143/Coppertone_Kids_Sunscreen_Stick%2C_SPF_30/

  19. Ever since they added UVB protection, I’ve noticed that the stuff gets EVERYWHERE and leaves grey/white stains on chairs, leather car seats, even handprints on cabinets. It’s gross. Any brands that are less disgusting? I wear a lot less of the stuff now, but my wife and kids still wear it and gets it all over everything. It did not used to be like this.

  20. I generally try to avoid the Yellow Face, but if I have to go out, Epicuren clear-drying zinc oxide is the best. It dries really…dry, so you don’t feel greasy. However, at $40 for 2.5 oz, it’s only for the face.

  21. That’s because, frankly, there already wasn’t such a thing. A sunscreen might be more water resistant than a competitor. But you can’t assume that one application of the “waterproof” stuff will stay with you through hours of pool time.

    I’ve surfed 8 hours straight in large waves with tons of thrashing around underwater with tropical sun bearing down on me. I don’t know about other brands, but clear Bullfrog stays on in those conditions and keeps me from burning wherever I put it. I was pleasantly surprised over the years to see Bullfrog grow from just surfers like me using it to the general populace.

    I honestly don’t know how healthy that kind of stuff is to be absorbed in the skin, but it definitely meets my definition of waterproof sun protection as far as burning goes.

    That said, before Bullfrog, I used to try other brands that claimed “waterproof” protection and I got burned.

  22. “I’ve surfed 8 hours straight in large waves with tons of thrashing around underwater with tropical sun bearing down on me.”

    That’s hot.

  23. Very nice. Now can they include info about which sunscreens will stain the @&$*! out of your clothing if you have iron in your water, like many of us on wells do? I can’t tell you how many light-colored shirts and shorts I’ve ruined from those orange stains – but the labels on the stuff is next to useless when it comes to staining.

  24. These experiments are done with people, volunteers who have sunscreen applied to some parts of their bodies, but not to others. Then, they’re exposed to UV light, and researchers measure how much longer it took the protected parts to burn compared to the unprotected parts.

    As someone who actually participated as a “lab rat” in one of these sunscreen tests during college (hey, it paid like 100 bucks!), what I found amusing (and wasn’t mentioned in this article, darnit) was that the parts of their bodies has to be areas “not previously exposed to sunlight”, or in other words, how the experiment got the nickname of the “ass-burning” experiment among my friends. (Of course a bunch of us did it- that’s beer and pizza money!)

    Sigh- I miss doing stupid things for free money in college.

  25. How dare the gubmint infringe on the freedom of speech rights of sunscreen manufacturers!!


  26. “Electrons dispel the energy by moving to a higher orbital,” Tan says. “Then they come back to stable lower orbitals.”

    Not exactly. Electrons absorb energy in the form of a photon (light particle) and use it to transition to a higher-energy orbital. Then they dissipate that light energy in a nonradiative (non-light-emitting) form, via vibrational and rotational energy. Like if someone goosed you (electron goes up) resulting in lots of little goosebumps (vibrational dissipation).

    Or something.

  27. Implying that most sunscreen has titanium dioxide in them?…

    Well if it is, it’s certainly not an active ingredient in the vast majority of the ones I find at my local stores. I know, because I’ve looked at every single sunscreen that is local. My wife is allergic to any sun screen that isn’t based on the zinc/titanium setup. So she mostly uses the Neutrogena Baby kind that’s like $3+ an ounce.

    And if it’s not an active ingredient then why use nano size? I would think the whole point of adding it would be to lighten or make the cream white…

    1. TiO2 is definitely a component in some sprays here. But TiO2 is photo-active too: it is used to make window panes UV-activated self cleaning.

      Thus, I wouldn’t think that it is more innocent than more complex organic molecules. OTOH TiO2 will stay more on the skin surface and it would have to activate another molecule first before that would delever energy somewhere in living skin?

  28. This is going to sound like a really dumb question, but how do I get a tan with high factor sunscreen?

    I’ve got a relatively dark complexion (Mediterranean), and wearing SPF15 sunscreen prevents sunburn even if I only apply it once in the morning. Am I taking a huge risk by doing this?

    1. The short answer is yes, it’s a risk. If you are tanning, you are damaging your skin and exposing yourself to increased risk of skin cancer. How much is hard to say, but it’s a myth that tans are safe(or even protective!) and that only burns increase your risk of cancer.

  29. “More and more Americans are using sunscreen. But that’s not the same thing as more Americans understanding sunscreen.”

    I’d be willing to bet you could pick almost any noun to replace “sunscreen,” and the statement would remain true.

  30. I always use sunscreen. That is, always since the day I forgot to put some on, went sailing, and ended up with sun poisoning and oozing sores all over the top half of my face. They took days to scab, and the scabs took weeks to come off.

    Oh, and I had blisters on the top of my earlobes, too. Puffy, fat blisters filled with serum. I didn’t think that was even possible.

    The threat of not using sunscreen is no longer abstract to me, nor to any of the people who saw me the next day…

  31. I also want to know more about how black people tan. My boyfriend is of the brown persuasion and insists on not wearing any sunscreen. This bothers me. I’m of the super pale persuasion and get burned if I’m in the sun for only 10 minutes. I know his color may not change as dramatically as mine, but I wonder if he still is at risk for cancer by not using sunscreen.

    1. White-skinned people get way more melanoma than dark-skinned people, but detection is a significant problem on dark skin.

  32. So, where were all the skin cancers before sunscreen? Certainly there were plenty of folks getting major exposure to their hands, necks, arms prior to these products.
    Not so long after sun_screen_ was brought to market we begin the ‘epidemic’ of skin cancer.

    1. Actually I collect old medical books of diseases of the skin and they had lots of skin cancers back then! They not only had cancers, they also didn’t know what to do with some of them and often got people in only after they had developed some amazingly disturbing symptom.

      History… it’s so much better when you don’t rely on your own recollection of the past.

    2. – The class of people who had any access to medical care, thus medical records, deliberately tried to stay as pale as possible as a sign of wealth and leisure.
      – Everybody stayed covered from neck to toe and wore gloves and hats, or went to jail for indecency.
      – Ozone layer?

      1. Cancer also used to be a fairly taboo subject; you would see a lot of families generalizing illness or calling it a mystery in public.

        1. A lot of people did not know the difference between certain cancers and syphilis. It was a sign of depravity, and thus very shameful. Since a lot of people have something to be ashamed of…

  33. The FDA? Another evil gubmint organization that steps on the throat of the corporations who want nothing but our good?

    When you use sunscreen, you’re sunbathing with Stalin!

  34. Australia has had these laws about honest sunscreen labeling for 20+ years. It tripped me out to see SPF 1,000,000+* sunscreens in stores in America. Do any brands in America currently list accurate figures for duration of waterproof effectiveness?


      1. And getting it removed doesn’t guarantee it not coming back and/or spreading to other parts of your body and killing you 10, 15, 20 years later.

  35. Another question.
    Why is the “good” sunscreen — the oxide-based kind — so much more expensive?
    Economies of scale?
    Simply more expensive?
    Low demand?

  36. 76 comments in and not a single mention of the humorous fact the sunscreen expert quoted is called Professor Tan?

    1. Actually, I count you as being the fourth to mention that so far…

      But don’t worry, I said the same thing when I was the second to mention it.

  37. Sunscreen is far too expensive, governments of the world need to subsidize it. The cost of subsidizing it would be easily paid for the money saved in skin cancer treatment.

  38. I have never understood why anyone would want to put a chemical on their skin that makes it not work properly. It’s insane.

  39. Maggie- you’d really enjoy speaking with John Barrow, a Harvard-educated, science-minded Aussie and entrepreneur based in Minneapolis. He started Coolibar.com several years ago and has been doing some extraordinary research in the area of sun protection.

  40. Thanks, Maggie, for shedding some light on the sunscreen issue. People are grossly misinformed about it and this helps. However, there is a lot more to consider. Things are more complicated than you describe and certainly more than anyone can cover in a 3 minute slot on Good Morning America or a 5 minute doctor’s visit. This video of a lecture by Edward Gorham, PhD at UDSD has the most thorough examination I have found:


    It is long and dull, but the guy is funny like my dad is funny…that is to say, not very, but endearing nonetheless.

    To summarize it as best I can (I know you could do way better!): UVA seems to cause melanoma (deadly) as it contains vastly more radiation. Both UBA and UVB can cause Basal Cell Carcinoma over years of tanning and burning but mostly in fairskinned people. Basal Cell Carcinoma is basically never deadly and is usually easily found and removed by a dermatologist. Both UVA and UVB cause melanin to be created deep in the skin. Melanin migrates to block cell nucleii from the radiation from UVA.

    Suncreens of ALL kinds prevent this process of melanin creation and protection from happening! It is important to get some sun. It is also important not to burn. Sunscreen that doesn’t contain Titanium Dioxide and Zinc Dioxide is WORSE than just getting sun until you start to burn because it blocks the UVB but doesn’t block UVA which is linked to Melanoma (deadly).

    I haven’t even mentioned Vitamin D yet, which is thought to be protective from cancer in general and is synthesized by the skin when exposed to the sun. It is synthesized in huge amounts, way more than you can get by any diet. Our skin is thought to have evolved with the sun, some evolving lighter pigmentation to synthesize more Vitamin D, some evolving darker pigmentation to have more protection from the radiation by the melanin.

    His advice is pretty simple really: Listen to your skin. If you burn easily, get a little sun (every day) and then cover up. If you tan, get a tan. Don’t burn. If you are dark skinned you need even more sun to make Vitamin D. If you start to burn, cover up. Go to a dermatologist to check for basal cell carcinoma every couple years for a mole check.

    I add: If you don’t want wrinkles, spots and moles, grow up. You’ll be happier if you’re healthy.

  41. One more important thing: he says melanin is red in some people (people who don’t tan, I suppose). I don’t remember how to tell if you are getting a healthy melanin-pink or burning. I tan, so that part didn’t sink into my long-term memory. Sorry.

    I also want to add that I wear a hat when I’m in the sun a while because it would be nice to avoid too many wrinkles on my face at least. I didn’t want to sound too snarky about that. Nobody wants to look old.

  42. ‘”Electrons dispel the energy by moving to a higher orbital,” Tan says. “Then they come back to stable lower orbitals.”‘

    If this is really what happens, then it worth noting that this process results in the emission of a photon – a “packet” of light – back out of the molecule equal in energy to the difference between the energy level of the orbital vacated by the electron and the orbital to which it drops. That photon, presumably, could go in any direction upon leaving the sunscreen, including back into your skin. Geometry would suggest that if the sunscreen molecule in question is positioned exactly on the surface of the skin, half of the stimulated photon emissions would do go into the skin and half would travel away from the skin. The wavelength of the emitted photon may or may not be better for you than the original light that came from the sun.

  43. All you need to know here:

    I recommend:
    “SPF 233—Close your eyes. Good. Now imagine a world without poverty and disease, where children of all races and religions join hands and sing old Negro spirituals, a place where the vicious cycles of boom and bust are replaced by never-ending Wonder Wheels of boom . . . and boom. SPF 233 is not inexpensive. But, in the war against the evil that is the sun, can you put a price on freedom?”

    1. One of the most hilarious, belly laugh inducing pieces of writing I’ve read in weeks. Thanks for the link.

  44. Using 2 milligrams per cm squared everyday you would prefer to buy a new one after 2 weeks! Anyway, some girls used to wear it just because avoiding getting darker skin. You can’t go outside under solar radiation without any protection. A label with “preventing cancers” shows a new generation for sunscreen!

  45. If for some reason the sun screen thing doesn’t work well for you, or you want to limit how much you spend on the stuff, and you want to be outside in the sun, you still have a few other options for low exposure to solar radiation.

    Wear a UPF shirt or a “rash guard shirt” when outside. The rash guard shirt is useful when swimming. You’d still need to apply sun screen to your face. Not swimming? Wear a broad-brimmed hat and a UPF shirt. Check places like Patagonia, REI, Sierra Trading Post, LL Bean, Lands End. A UPF or rash guard shirt doesn’t get sweated off and you needn’t re-apply after a number of hours spent in the water. A rash guard shirt means no chemical warfare on marine life. Sure, the manufacturing process and fiber of that shirt is petroleum-o-riffic, but one decent shirt will last way longer than plastic tubes and bottles of annually purchased goo.

    Wearing one of these shirts also mean you don’t to wait the requisite 30-45 minutes so often specified in sun screen package directions. If you’re not applying your sun screen, then waiting 30 minutes before solar exposure and/or entering water, you’re doing it wrong. Sun screen needs time to sink into your skin in order to perform.

    Other option? Avoid the sun during its strongest period of radiation when it’s at its highest angles in the sky (for North Americans that’s something like 10 am – 4 pm).

    1. “Other option? Avoid the sun during its strongest period of radiation when it’s at its highest angles in the sky (for North Americans that’s something like 10 am – 4 pm). ”

      if that’s the final word i’ll take it, but i remember coming across an article proposing that the low-angle times of day might be worse???

      and then there’s this: “Ultraviolet B (UVB): wavelength 280–315 nm. UVB can cause sunburn yet is also what enables vitamin D production in the skin. Depending upon the angle at which the sun’s rays reach the earth, optimal UVB exposure is between 10:00 am–2:00 pm and in the summer (70% of a person’s yearly dose is received in summer). UVB does not penetrate glass and most is blocked by the ozone layer.”

      so the best time of day to get cancer is also the best time to prevent it. i now see the value of those uv disc thingies they sell through thinkgeek– maybe. i think.

  46. Visible light certainly can be scattered by particles smaller than the wavelength. It’s why the sky is blue.

  47. Very nice information. This message should be shared by everyone. This cosmetice peolpe making fool to us. This is really very unethical. If you are selling something must have some fact and it should work by making fool you can’t survive for a longer period.

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