By Bahar Gholipour, Staff Writer

Published: 07/30/2013 06:45 AM EDT on LiveScience


If you've heard it once, you've heard it a thousand times: putting on sunscreen and avoiding too much direct sunlight are important in preventing skin damage, signs of aging and cancer.


But this wasn't always a given. Although in many cultures people used to cover their bodies with oils, extracts, hats and clothing when venturing into the sun, people once thought that the sun's heat, rather than its radiation, caused the painful redness of sunburns[1] .


One of the first experiments showing that something other than heat burns the skin was done by Sir Everard Home, an English physician, in 1820. Home exposed one of his hands to the sun, while covering the other with a black cloth. Only the exposed hand got sunburnt, but a thermometer showed the temperature around the covered hand was a few degrees higher.


Later, in 1889, Johan Widmark proved that it was mainly the ultraviolet rays, rather than luminous rays, that caused the redness of sunburned skin. His findings preceded the first medical recommendations of protection against sunlight, advice that continues to this date.


Sunscreens have since been evolving -- from pastes to creams, to lotions and sprays, and perhaps someday a pill. Here are five interesting things to learn about sunscreens:


1. Early sunscreens



Apart from umbrellas and hats, ancient cultures used a variety of sunscreens made from herbal extracts or mineral crusts to protect against the sun's rays. These early sunscreens included ingredients like rice bran oil, iron, clay and tar.


In more contemporary times, sunscreens were developed from horse chestnut extracts in the 1910s. This pasty sunscreen was sold under the name of Zeozon. In the 1930s, Ambre Solaire was introduced, an oily sunscreen that was easier to apply to the skin.


Sunscreens have even been subject to "Top Secret" military research. In the 1940s, the U.S. Army and Air Force asked the American Medical Association for advice about the most effective sunscreen for soldiers. Researchers examined the effectiveness of 12 compounds and concluded that red veterinary petrolatum can be an effective, waterproof sunscreen.


One of biggest steps in sunscreen's development has been the transition from the white paste of early sunscreens to an almost invisible cream. In older sunscreens, the light-reflecting compounds could appear white because they were not small enough. With nanotechnology[2] , however, ingredients such as titanium dioxide are turned into small, invisible particles.


2. How does sunscreen work?


Sunscreens can be made of two types of ingredients: inorganic particles, such as titanium dioxide or zinc oxide, or organic components, such as herbal extracts or compounds like oxybenzone.


The particles in sunscreens provide physical protection against UV rays by blocking or reflecting sunlight. Organic components absorb UV rays and release their energy as heat, providing chemical protection.


Dr. Shannon Trotter, professor of dermatology at the Ohio State University, says it is optimal to use a combination of both types of sunscreen, those providing chemical protection and those offering physical defenses. You can tell which is which by looking at the labeling required by the FDA[3] .


Most sunscreens today have both types of ingredients.


The concept of sun protection factor (SPF) was introduced in the 1960s. SPF indicates how long a sunscreen protects the skin. Physicians recommend SPF 15 and SPF 30. Higher SPFs may not actually provide longer hours of protection, especially because the cream is usually washed off or absorbed after two hours.


3. Does sunscreen prevent people from getting vitamin D?


The body needs sunlight to produce vitamin D. So should we worry that wearing sunscreen may lead to vitamin D deficiency?


Studies have yielded mixed results, but large trials have shown that although sunscreen does lower the amount of vitamin D produced by the skin, these effects are not significant.


The American Academy of Dermatology does not recommend getting vitamin D from sun exposure; instead, the academy recommends getting this nutrient from the diet, by eating foods naturally rich in vitamin D[4] , and from vitamin supplements. Foods that have high levels of vitamin D include fish oil, salmon and sardines, soy milk, eggs, fortified dairy products and mushrooms.


4. The most recent sunscreens: spray-ons


The innovation of spray-on sunscreen brought ease of application to a whole new level. But are these products effective and safe?


Recently, the FDA warned against wearing spray-on sunscreen near open flames. In five incidents, people wearing the spray-on protection near sources of flame suffered significant burns. Although the specific products linked with these cases were recalled and are no longer on the shelf, many other spray-on sunscreen products may contain flammable ingredients, such as alcohol, and could catch on fire if they are too close to flames.


Trotter said spray-on sunscreen is effective if applied properly[5] . "Some people spray it from too far away and only get a mist," she said, "The biggest challenge is to know how you actually use enough to cover all the areas of the body."


Another concern with sprays is toxicity. The FDA is investigating the health risks of accidentally inhaling spray-on sunscreen. Trotter recommended using a lotion for areas near the mouth and using spray for hair-bearing areas where it's difficult to apply a cream.


5. Little bites to remember


You need a volume of one shot-glass–worth of sunscreen to cover the body, and you should apply sunscreen 15 minutes before going outdoors. Don't forget the lips, Trotter said.


The Centers for Disease Control and Prevention recommends using a broad-spectrum sunscreen that protects against UV-A and UV-B rays, and has an SPF of at least 15. People should check the expiration date, because some sunscreen ingredients might degrade over time or develop bacterial growth.


It's also recommended that people with oily skin or those who are prone to acne use a water-based sunscreen. And people sensitive to para-aminobenzoic acid (PABA) should buy brands that do not contain the compound.


The FDA recommends not applying sunscreen on babies younger than 6 months old. Instead, babies should be placed in shady areas or covered with clothing[6] .


Email Bahar Gholipour[7] or follow her @alterwired . Follow LiveScience @livescience[9] , Facebook[10] & Google+[11] . Original article on LiveScience.com[12] .[8]



Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. ]]>

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  • The first sunscreen mistake is not wearing any. By now, we all know spending too much time in the sun can <a href="http://www.fda.gov/drugs/resourcesforyou/consumers/buyingusingmedicinesafely/understandingover-the-countermedicines/ucm239463.htm" target="_hplink">increase risk for both skin cancer</a> (the <a href="http://www.cancer.org/cancer/cancercauses/sunanduvexposure/skin-cancer-facts" target="_hplink">most common of all cancers</a>) and premature skin aging. On top of that, <a href="http://www.huffingtonpost.com/2013/06/03/sunscreen-skin-aging-_n_3380828.html" target="_hplink">a new Australian study</a> out this week found daily sunscreen use could slow skin aging. But even those of us with the best intentions can make mistakes when it comes to sunscreen -- mistakes that can be costly for our skin. So now that summer is almost upon us, we asked David J. Leffell, M.D., professor of dermatology and surgery at the Yale School of Medicine, and Lisa Garner, a dermatologist in practice in Garland, Texas, to sort through eight of the most common mistakes. First, a caveat: SPF, which stands for sun protection factor, applies only to the sunburn-causing UVB rays, meaning you'll need to look for the words "broad spectrum" somewhere on the bottle to address the skin-damaging UVA rays. For more on how to choose the right sunscreen for you, <a href="http://www.huffingtonpost.com/2013/06/03/sunscreen-skin-aging-_n_3380828.html" target="_hplink">click here</a>.




  • You've Been Using The Same Bottle For The Past Three Summers


    When it comes to sunscreen, expiration dates really do matter. The active ingredients in sunscreen can deterioriate over time, Garner says, which means the protection won't be as effective. What's more, an open bottle is more likely to become contaminated with germs over time, as the preservatives meant to prevent that can also lose their efficacy. You might want to read the suggested storage conditions on the label, too -- stuffing your bottle in a glove compartment or a beach-bag in the trunk might be convenient, but exposure to hot temperatures can hamper effectiveness, Leffell says.




  • You Count On The SPF In Your Makeup To Do The Trick


    A two-in-one foundation/sunscreen certainly seems handy, but that doesn't mean it works. Part of the problem is quantity: a dab of foundation isn't the same as the amount of sunscreen you'd slather on your face. "I don't think that most women wear heavy enough makeup to get an adequate SPF from their makeup," Garner tells HuffPost. Makeup also wears off during the day ("I can't even tell I put any on this morning now that it's the end of the day," she says), and chances are you aren't religiously re-applying the way you should with sunscreen. "It's a good belt and suspenders approach but I would not rely on sunscreen in a product that was intended for another purpose," Leffell says. In other words, if your foundation promises some added protection, great. But you still need to apply the real deal under your makeup every day. The good news? If you're bent on a two-in-one product, moisturizer with SPF <em>does</em> do the trick.




  • You Only Use A Dab


    When it comes to sunscreen, less is <em>not</em> more. But in the real world <a href="http://onlinelibrary.wiley.com/store/10.1111/phpp.12017/asset/phpp12017.pdf?v=1&t=hhhp4xtq&s=7e66c77e342f5dd3f350bb9292fe75fa3d39e9da" target="_hplink">many of us don't use</a> enough, which means the white stuff can't live up to its full protective potential. The classic rule of thumb is to slather on about a shot glass full of sunscreen to cover the whole body. The problem with that advice, though, is that a 110-pound woman is going to have less surface area than, say, a 250-pound man, Leffell explains. "I avoid giving specific amounts," he says. "Use enough to evenly cover the skin and massage it in, and be systematic about it." When in doubt, slather more on: Both experts agree there's no such thing as too much. "It's always more than you think you should put on," Garner says. (She also recommends the "teaspoon rule" to figure out how much to apply on exposed skin when you're clothed -- for more on that <a href="http://onlinelibrary.wiley.com/store/10.1111/phpp.12017/asset/phpp12017.pdf?v=1&t=hhhp4xtq&s=7e66c77e342f5dd3f350bb9292fe75fa3d39e9da" target="_hplink">click here</a>.)




  • You Put Your Sunscreen On At The Beginning Of The Day -- And Forget About It After That


    "If you're in the sun, your sunscreen is good for a max of two hours, and depending on the sunscreen it might not even last that long," Garner says. The skin literally "uses up" the active ingredient in the lotion over time, meaning it can't do any more. Sweating and swimming causes the sunscreen to wear off even faster, so consider reapplying every hour in those conditions. And be sure to let the reapplied sunscreen soak into the skin for a few minutes before diving back into the water, otherwise it'll wash right off.




  • You Count On Waterproof Sunscreen When You're Swimming


    Turns out, there isn't such a thing as "waterproof" sunscreen. In fact, a relatively <a href="http://www.fda.gov/forconsumers/consumerupdates/ucm258416.htm" target="_hplink">recent iteration of FDA rules</a> no longer even allows the word to be used on sunscreen bottles (along with "sweat-proof" or "sunblock"). Instead, based on testing, they can claim to be "water resistant" for either 40 or 80 minutes. After that? Reapply, reapply, reapply. "I can't tell you how many patients come in and say, 'But I put my sunscreen on,'" Garner says. "[But] did you put it back on?"




  • You Only Apply Sunscreen On Sunny Days


    A cloudy day is <em>not</em> a sunscreen hall pass. Just because you can't see (or feel the heat from) the sun doesn't mean it's not doing damage. "UV penetrates through haze and fog and you can easily get a sunburn," Leffell says. "UV radiation is invisible: you can't smell it, taste it, hear it, see it." And that means it doesn't necessarily need to be warm or sunny to cause some real damage, whether or not you see it. "People only think they need to put sunscreen on when it's hot," Garner says. "It never fails that here in Texas I see several sunburns in March." UVA rays, which penetrate the skin more deeply and are a culprit in skin aging, in particular, can reach the skin even through thick clouds (and glass, for that matter).




  • You Shell Out The Big Bucks For The Highest SPF Possible


    Many skin experts recommend using a sunscreen that carries an SPF of at least 30. So does that mean SPF 60 is <em>twice</em> as protective, or lasts twice as long? Nope, according to the experts. An SPF of 30, when applied in the appropriate amount, will block out about 96 percent of the sunburn-causing UVB rays from the sun, Garner says. As you go up from there, you only see a very small difference (about 98 percent with SPF 50 and still under 99 percent with SPF 75) -- there's no way to block out 100 percent of the sun's rays with sunscreen. If you feel more comfortable with those extra couple of percentage points, go for it. But it doesn't change how often you'll need to reapply or how long you can be in the sun.




  • You Count On Sunscreen For Total Sun Protection


    Your sunscreen can't block out 100 percent of the sun's UVB rays, and it shouldn't be your only defense against sun damage. "Sunscreen does not protect you completely from the sun," Garner says. The rest of the work -- wearing a hat, sunglasses and protective clothing and avoiding the sun during the most intense hours -- is up to you. Remember, too, that sunscreen isn't a free pass to spend the day baking in the sun. "Sunscreen should be used to protect you when you have to be in the sun during the intense part of the day," she says. "It should not be used to allow you to be in the sun longer just because you want to." And avoiding a burn doesn't mean you've properly protected your skin, she adds: "Once you've tanned, you've damaged skin."