Ultraviolet Light and Sun Protection
What Are Sunscreens?
Sunscreens are chemical agents that help prevent the sun's ultraviolet (UV) radiation from reaching the skin. Two types of ultraviolet radiation, UVA and UVB damage the skin and increase your risk of skin cancer.
UVB is the chief culprit behind sunburn, while UVA rays, which penetrate the skin more deeply, are associated with wrinkling, leathering, sagging, and other effects of photoaging. They also exacerbate the carcinogenic effects of UVB rays, and increasingly are being seen as a cause of skin cancer on their own. Sunscreens vary in their ability to protect against UVA and UVB.
What Is Ultraviolet Radiation?
UV radiation is part of the electromagnetic (light) spectrum that reaches the earth from the sun. It has wavelengths shorter than visible light, making it invisible to the naked eye. These wavelengths are classified as UVA, UVB, or UVC, with UVA the longest of the three at 320–400 nanometers (nm, or billionths of a meter). UVA is further divided into two wave ranges, UVA I, which measures 340-400 nanometers (nm, or billionths of a meter), and UVA II which extends from 320–400 nanometers. UVB ranges from 290 to 320 nm. With even shorter rays, most UVC is absorbed by the ozone layer and does not reach the earth.
Both UVA and UVB, however, penetrate the atmosphere and play an important role in conditions such as premature skin aging, eye damage (including cataracts), and skin cancers. They also suppress the immune system, reducing your ability to fight off these and other maladies.
UV Radiation and Skin Cancer
By damaging the skin’s cellular DNA, excessive UV radiation produces genetic mutations that can lead to skin cancer. Both the U.S. Department of Health and Human Services and the World Health Organization have identified UV as a proven human carcinogen. UV radiation is considered the main cause of nonmelanoma skin cancers (NMSC), including basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). These cancers strike more than a million and more than 250,000 Americans, respectively, each year. Many experts believe that, especially for fair-skinned people, UV radiation also frequently plays a key role in melanoma, the deadliest form of skin cancer, which kills more than 8,000 Americans each year.
UVA
Most of us are exposed to large amounts of UVA throughout our lifetime. UVA rays account for up to 95 percent of the UV radiation reaching the Earth’s surface. Although they are less intense than UVB, UVA rays are 30 to 50 times more prevalent. They are present with relatively equal intensity during all daylight hours throughout the year, and can penetrate clouds and glass.
UVA, which penetrates the skin more deeply than UVB, has long been known to play a major part in skin aging and wrinkling (photoaging), but until recently scientists believed it did not cause significant damage in areas of the epidermis (outermost skin layer) where most skin cancers occur. Studies over the past two decades, however, show that UVA damages skin cells called keratinocytes in the basal layer of the epidermis, where most skin cancers occur. (Basal and squamous cells are types of keratinocytes.) UVA contributes to and may even initiate the development of skin cancers.
UVA is the dominant tanning ray, and we now know that tanning, whether outdoors or in a salon, causes cumulative damage over time. A tan results from injury to the skin’s DNA; the skin darkens in an imperfect attempt to prevent further DNA damage. These imperfections, or mutations, can lead to skin cancer.
Tanning booths primarily emit UVA. The high-pressure sunlamps used in tanning salons emit doses of UVA as much as 12 times that of the sun. Not surprisingly, people who use tanning salons are 2.5 times more likely to develop squamous cell carcinoma, and 1.5 times more likely to develop basal cell carcinoma. According to recent research, first exposure to tanning beds in youth increases melanoma risk by 75 percent.
UVB
UVB, the chief cause of skin reddening and sunburn, tends to damage the skin’s more superficial epidermal layers. It plays a key role in the development of skin cancer and a contributory role in tanning and photoaging. Its intensity varies by season, location, and time of day. The most significant amount of UVB hits the U.S. between 10 AM and 4 PM from April to October. However, UVB rays can burn and damage your skin year-round, especially at high altitudes and on reflective surfaces such as snow or ice, which bounce back up to 80 percent of the rays so that they hit the skin twice. UVB rays do not significantly penetrate glass.
Protective Measures
Protect yourself from UV radiation, both indoors and out. Always seek the shade outdoors, especially between 10 AM and 4 PM. And since UVA penetrates glass, consider adding flat, tinted UV-protective film to your car’s side and rear windows as well as to house and business windows. This film blocks up to 99.9 percent of UV radiation and lets in up to 80 percent of visible light.Outdoors, dress to limit UV exposure: Special sun-protective clothes with UPF (ultraviolet protection factor) indicate how much UV radiation can penetrate the fabric; the higher the UPF, the better. A shirt with an UPF of 30, for example, means that just 1/30th of the sun’s UV radiation can reach the skin. Laundry additives can also be washed right into regular fabrics to provide higher UPFs. However, you can enhance your sun safety simply by learning to evaluate everyday fabrics’ sun protection qualities and choosing those with the best protection. For instance, bright- or dark-colored, lustrous clothes reflect more UV radiation than do pastels and bleached cottons; and tightly woven, loose-fitting clothes provide more of a barrier between your skin and the sun. Finally, broad-brimmed hats and UV-blocking sunglasses help shield the sensitive skin on your head, neck, and around the eyes — areas that usually sustain a lot of sun damage.
Sun Protection Factor (SPF) and UV Radiation
Since the advent of modern sunscreens, a sunscreen’s efficacy has been measured by its sun protection factor, or SPF. SPF is not an amount of protection per se. Rather, it indicates how long it will take for UVB rays to redden skin when using a sunscreen, compared to how long skin would take to redden without the product. For instance, someone using a sunscreen with an SPF of 15 will take 15 times longer to redden than without the sunscreen. An SPF 15 sunscreen screens 93 percent of the sun’s UVB rays; SPF 30 protects against 97 percent; and SPF 50, 98 percent. The Skin Cancer Foundation maintains that SPFs of 15 or higher are necessary for adequate protection.
Sunscreen Ingredients
Since both UVA and UVB are harmful, you need protection from both kinds of rays. To make sure you’re getting effective UVA as well as UVB coverage, look for a sunscreen with an SPF of 15 or higher, plus some combination of the following UVA-screening ingredients: stabilized a avobenzone, ecamsule (a.k.a. Mexoryl™), oxybenzone, titanium dioxide, and zinc oxide. You may see the phrases multi spectrum, broad spectrum or UVA/UVB protection on sunscreen labels, and these all indicate that some UVA protection is provided. However, because there is no consensus on how much protection these terms indicate, such phrases may not be entirely meaningful.
There are currently 17 active ingredients approved by the FDA for use in sunscreens. These filters fall into two broad categories: chemical and physical. Most UV filters are chemical: They form a thin, protective film on the surface of the skin and absorb the UV radiation before it penetrates the skin. The physical sunscreens are insoluble particles that reflect UV away from the skin. Most sunscreens contain a mixture of chemical and physical active ingredients.
FDA-Approved Sunscreens |
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Active Ingredient/UV Filter Name |
Range Covered |
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UVA1: 340-400 nm |
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UVA2: 320-340 nm |
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UVB: 290-320 nm |
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Chemical Absorbers: |
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Aminobenzoic acid (PABA) |
UVB |
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Avobenzone |
UVA1 |
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Cinoxate |
UVB |
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Dioxybenzone |
UVB, UVA2 |
|
Ecamsule (Mexoryl SX) |
UVA2 |
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Ensulizole (Phenylbenzimiazole Sulfonic Acid) |
UVB |
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Homosalate |
UVB |
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Meradimate (Menthyl Anthranilate) |
UVA2 |
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Octocrylene |
UVB |
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Octinoxate (Octyl Methoxycinnamate) |
UVB |
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Octisalate ( Octyl Salicylate) |
UVB |
|
Oxybenzone |
UVB, UVA2 |
|
Padimate O |
UVB |
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Sulisobenzone |
UVB, UVA2 |
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Trolamine Salicylate |
UVB |
Physical Filters: |
|
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Titanium Dioxide |
UVB, UVA2 |
|
Zinc Oxide |
UVB,UVA2, UVA1 |
What Is SPF?
Most sunscreens with an SPF of 15 or higher do an excellent job of protecting against UVB. SPF — or Sun Protection Factor — is a measure of a sunscreen's ability to prevent UVB from damaging the skin. Here's how it works: If it takes 20 minutes for your unprotected skin to start turning red, using an SPF 15 sunscreen theoretically prevents reddening 15 times longer — about five hours.
Another way to look at it is in terms of percentages: SPF 15 blocks approximately 93 percent of all incoming UVB rays. SPF 30 blocks 97 percent; and SPF 50 blocks 98 percent. They may seem like negligible differences, but if you are light-sensitive, or have a history of skin cancer, those extra percentages will make a difference. And as you can see, no sunscreen can block all UV rays.
But there are problems with the SPF model: First, no sunscreen, regardless of strength, should be expected to stay effective longer than two hours without reapplication. Second, "reddening" of the skin is a reaction to UVB rays alone and tells you little about what UVA damage you may be getting. Plenty of damage can be done without the red flag of sunburn being raised.
Who Should Use Sunscreen?
Anyone over the age of six months should use a sunscreen daily. Even those who work inside are exposed to ultraviolet radiation for brief periods throughout the day. Also, UVA is not blocked by most windows.
Children under the age of six months should not be exposed to the sun. Shade and protective clothing are the best ways to protect infants from the sun.
What Type of Sunscreen Should I Use?
The answer depends on how much sun exposure you're anticipating. In all cases we recommend a broad-spectrum sunscreen offering protection against both UVA and UVB rays.
Many after-shave lotions and moisturizers have a sunscreen (usually SPF 15 or greater) already in them, and this is sufficient for everyday activities with a few minutes here and there in the sun. However, if you work outside or spend a lot of time outdoors, you need stronger, water-resistant, beachwear-type sunscreen that holds together on your skin. The "water resistant" and "very water resistant" types are also good for hot days or while playing sports, because they're less likely to drip into your eyes. However, these sunscreens may not be as good for everyday wear. They are stickier, don't go as well with makeup, and need to be reapplied every two hours.
Many of the sunscreens available in the US today combine several different active chemical sunscreen ingredients in order to provide broad-spectrum protection. Usually, at least three active ingredients are called for. These generally include PABA derivatives, salicylates, and/or cinnamates (octylmethoxycinnamate and cinoxate) for UVB absorption; benzophenones (such as oxybenzone and sulisobenzone) for shorter-wavelength UVA protection; and avobenzone (Parsol® 1789), ecamsule (Mexoryl™), titanium dioxide, or zinc oxide for the remaining UVA spectrum.
How Much Sunscreen Should I Use and How Often Should I Put it On?
To ensure that you get the full SPF of a sunscreen, you need to apply 1 oz – about a shot glass full. Studies show that most people apply only half to a quarter of that amount, which means the actual SPF they have on their body is lower than advertised. During a long day at the beach, one person should use around one half to one quarter of an 8 oz. bottle. Sunscreens should be applied 30 minutes before sun exposure to allow the ingredients to fully bind to the skin. Reapplication of sunscreen is just as important as putting it on in the first place, so reapply the same amount every two hours. Sunscreens should be reapplied immediately after swimming, toweling off, or sweating a great deal.
Common Myths
Wearing sunscreen can cause vitamin D deficiency.
There is some controversy regarding this issue, but few dermatologists believe (and no studies have shown) that sunscreens cause vitamin D deficiency. Also, vitamin D is available in dietary supplements and foods such as salmon and eggs, as well as enriched milk and orange juice. Obtain your vitamin D through food and vitamin supplements.
If it's cold or cloudy outside, you don't need sunscreen.
This is not true. Up to 40 percent of the sun's ultraviolet radiation reaches the earth on a completely cloudy day. This misperception often leads to the most serious sunburns, because people spend all day outdoors with no protection from the sun.
Eighty percent of your sun exposure comes as a child, so it's too late to do anything now.
It appears that this universally promoted idea was based largely on a misinterpretation. A recent multi-center study showed that we get less than 25 percent of our total sun exposure by age 18. In fact, it is men over the age of 40 who spend the most time outdoors, who get the highest annual doses of UV rays. And since adult Americans are living longer and spending more leisure time outdoors, preventing ongoing skin damage will continue to be an important part of a healthy lifestyle.
Buy a high-quality product with an SPF of 15 or higher; check its ingredients to make sure it offers broad-spectrum protection; and decide whether it works better for everyday incidental use or extended outdoor use. Once you choose the right sunscreen, use it the right way. But remember, you should not rely on sunscreen alone to protect your skin against UV rays. By following simple prevention guidelines, you can lower your risk of developing skin cancer, while helping your skin look younger, longer.
