What is Ultraviolet Radiation (UV) and UVA or UVB?

For a six billion-year-old star, the sun is certainly in the news a lot lately, mainly because it is still a source of uncertainty and confusion to many of us.The center of this confusion is the sun’s ultraviolet A (long-wave) and ultraviolet B (shortwave) rays. Our understanding of exactly what kinds of damage each causes to the skin, and how best to protect ourselves, seems to shift every year as new research comes out. For example, it was once thought that only UVB was of concern, but we keep learning more and more about the damage caused by UVA. And new, improved forms of protection against UVA keep emerging. Keeping up with these new developments is a worthwhile challenge that can help all of us prevent sun damage.

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.

Home Treatments When You Get Sun Burned

Home remedies may provide some relief from a mild sunburn. Remember a sun burn is a like any other burn from heat in which the cells become damaged. Be gentle and try not to further irritate the area.

Use cool cloths on sunburned areas, you should gently pat to allow the heat to disperse from the cloth after it absorbs the heat from the sun burn. You can try to take frequent cool showers or baths also.

Apply soothing lotions that contain Aloe Vera to sunburned areas. Topical steroids (such as 1% hydrocortisone cream) may also help with sunburn pain and swelling. Note: Do not use the cream on children younger than age 2 unless your doctor tells you to. Do not use in the rectal or vaginal area for yourself or in children younger than age 12 unless your doctor tells you to.

There is little you can do to stop skin from peeling after a strong sunburn-it is part of the healing process. However application of a good natural or organic lotion may help because it will increase the antioxidants in the sunburned area and speed up the cell rejuvenation process. In addition lotion may help relieve the itching once the skin has started to peel.

A sunburn can cause a mild fever and a headache. Lie down in a cool, quiet room to relieve the headache. A headache may be caused by dehydration, so drinking fluids may help.

Other natural home treatments, such as essential oils like lavender, geranium, or calendula, may help relieve your sunburn symptoms.

You can try a nonprescription medicine to help treat your fever or pain, aspirin is great for lessening the effects of a burn if taken soon enough.

* Acetaminophen, such as Tylenol for pain and fever
* Nonsteroidal anti-inflammatory drugs (NSAIDs) for swelling from the burn
* Ibuprofen, such as Advil or Motrin for pain and fever
* Aspirin (also a nonsteroidal anti-inflammatory drug), such as Bayer for pain, fever and to thin the blood which will help reduce the burn

Talk to your doctor or your child’s doctor before switching back and forth between doses of acetaminophen and ibuprofen. When you switch between two medicines, there is a chance you or your child will get too much medicine.

Protection Daily from Sun Exposure for Healthy and Safe Skin

Some experts claim over half of sun damage occurs during our every day activities – walking to the car, going in and out of buildings, walking along the street shopping, and so on – not while we’re sunbathing. Unfortunately, this means we should to wear sunscreen just about every time we leave the house. Most sunscreens are fairly toxic and organic sun care is blooming. More products are becoming available that are organic, natural and eliminate harmful toxins. This is great news for all of us especially our younger ones and babies.

Remeber organic sunblock is only one step you can take to protect yourself from the sun. Covering up can be just as important as the type of skin care or sun care product you use. The clothes we would prefer on a warm summer day – lightweight, light-colored clothing made with loosely-woven fabric – do not offer much protection. That’s why kids who swim with T-shirts over their bathing suit still get burned.

To completely block UV rays you need clothing with a ultraviolet protection factor (UPF) of about 1700. A white T-shirt has a UPF of seven. The same T-shirt in green has a UPF of 10. A dark, thick fabric like velvet comes in at about 50. To reach 1700 you’d need a long-sleeved dark denim shirt. Not exactly anyone’s idea of fun in the sun.

The long and short of it is that while we may be willing and able to cover up with high UPF clothing in some circumstances, there’s no way that’s going to fly at the beach. So, you’re going to have to resort to sunscreen, and, to be safe, you’re going to need a skin care product that protects you from the sunscreen’s dangerous chemical ingredients.

How do you do that? Your first line of defense is natural sunscreen – check your local health food store. However, not all these products are completely toxic free so you’ll still some additional protection. Your best bet for that is a shielding lotion: A good shielding lotion bonds with the outer layer of the skin to form a new protective layer that keeps out chemicals. It also locks in natural moisture – another thing you have to be concerned with when you’re out in the sun: sunburn equals dehydration.

Summer sun care can be complex but remeber its sunlight is good. Try to use organic sunscreen, appropriate clothing, and a natural after sun lotion. These natural skin care products can help you enjoy your summer without concern for your health.

Sun Protection and Sun Burn FAQ

1. “How Much Sunscreen Should I Apply?”

The average user of sunscreen tends to use significantly less sunscreen than the amount required to achieve the SPF listed on the container.

2. “How Often Should I Apply Sunscreen When I’m Out In The Sun?”

Many experts recommend that frequent application during sun exposure is required. However, a group of children were tested by spreading on 1 application of sunscreen to one side of their bodies, and four applications to the other.

They then spent 6 hours in the sun. One application provided the same level of protection as four applications, confirming the adequacy of a single daily application of a sunscreen in that situation.

3. “How Long Before Sun Exposure Should I Apply Sunscreen To My Skin?”

As molecules of sunscreen are present in their active state in the sunscreen, sunscreens work immediately upon application. The only reason for application early is to allow absorption into the skin so that the sunscreen is less likely to be washed off, should the person be entering the water. Even so, modern sunscreens are quite resistant to removal from the skin.

4. “Sun Protection Factor (SPF) – What Is It?”

SPF is the ratio of the minimal ultraviolet dose required to produce redness with and without a sunscreen. For example, if it took ½ hour for your skin to become sunburned without any sunscreen, then for a sunscreen that has a 15 SPF rating, you could stay in the sun for 15 times longer (or 7.5 hours) before you get sunburned. This is provided, of course, that you’ve applied the sunscreen properly so that you’re getting the prescribed protection.

5. “Reactions To Sunscreens?”

Sunscreens can be both an irritant and an allergen, though allergic reactions are rare. Irritant reactions, however, abound. One classic error in sunscreen application is to put a large amount of sunscreen on the forehead. Perspiration and gravity can cause the sunscreen to migrate down your forehead into your eyes, causing a stinging sensation. Some people attribute this to an allergic reaction and discontinue use. It’s also important to wash your hands after applying sunscreen, since rubbing your sunscreen covered finger near your eyes can induce an irritant reaction.

6. “Why Is It Important To Use Sunscreens During Childhood?”

It appears that a great deal of time can elapse between actual sun damage and the development of skin cancer or other skin problems like photoaging. Therefore, it is important to protect your skin from an early age when you are out in the sun.

7. “Sunscreens And The Elderly?”

Many elderly people can become quite obsessed by sun avoidance, and their quality of life can suffer. Sometimes, if they are diagnosed with an actinic keratosis or basal cell carcinoma, they can become anxious and almost leap from shadow to shadow. However, few of them are likely to develop new skin cancers from present sun exposure. As long as they are prudent about avoiding excessive sun exposure and protecting their skin to prevent sunburn, they can continue to enjoy time outdoors.

8. “Can Sunscreens Prevent Cancer?”

There is clear evidence that sunscreens are helpful in preventing actinic keratoses, which are warty lesions that can occur on sun-exposed skin of the face or hands. Research has shown that these lesions can develop into a cancer called squamous cell carcinoma, and that this is linked to a cumulative exposure to the sun.

However, there is surprisingly little evidence that sunscreens have much effect in preventing another kind of skin cancer called basal cell carcinoma, or for malignant melanoma. For malignant melanoma and for basal cell carcinoma, the character and timing, that is, the type of sunlight and your age at the time of the exposure to the sun appears to be more important than the cumulative dose.

Overexposure to the Sun Can Happen Indoors and Outdoors

Journal of the American Academy of Dermatology article offers information about the recent development in sun protection provided by window and automobile glass, and sunglasses.

In the car, at work or walking to and from a store, you can’t escape the sun’s ultraviolet (UV) rays. However, new research about the transmission of UV light through window and automobile glass and through sunglasses, has led to developments that can help protect people from the sun.

“People should realize that even during everyday activities they are receiving incidental sun exposure which harms the skin as it accumulates and can result in premature aging, wrinkles and even skin cancer,” said dermatologist Henry W. Lim, M.D., chairman of the department of dermatology, Henry Ford Hospital in Detroit, Mich., and co-author of the Journal of the American Academy of Dermatology article entitled, “Photoprotection by window glass, automobile glass and sunglasses.” “Dermatologists and manufacturers of glass products and sunglasses are continually working to find better ways to decrease the amount of UV radiation being filtered through these items to the skin and eyes. These advances are helping to reduce the amount of UV exposure that a person receives on a daily basis.”

UV radiation from the sun comes in two forms: ultraviolet A (UVA) and ultraviolet B (UVB). UVB has long been associated with sunburn while UVA has been recognized as a deeper penetrating radiation that contributes to premature aging and wrinkle formation. Both of these types of rays have been linked to the development of skin cancer. More than 1 million new cases of skin cancer are diagnosed each year.

Window Glass and Photoprotection

Window glass filters out UVB rays, but UVA rays are still transmitted to the skin through the panes. The type of glass and the type of coating on the glass can affect the percentage of UV radiation that is transmitted to the body.

Most residential buildings have one of three types of glass: clear, tinted or reflective. Of these three, reflective glass, the kind that eliminates the ability to see the interior of a building from the outside during the day, minimizes unwanted solar heat gain and reduces UV transmission to less than 25 percent. This means nearly one-quarter of the UV exposure, exclusively the longer wavelength UVA, is reaching the inside though, remarked Dr. Lim.

“Most Americans spend 80 percent of their day indoors at work or school,” stated Dr. Lim. “With the new trend in architecture toward more and larger windows in buildings, protection from UV exposure when indoors has become an important issue for not only the cost-effectiveness of cooling a building, but also for the health and safety of the employees who work within it.”

Recent developments in window glass include low-emissivity (low-E) glass which has a special surface coating between layers of antireflective glass. This type of glass reflects up to 70 percent of solar heat and reduces UV transmission through the panes to 20 percent.

To protect the skin from the damaging rays of the sun when working indoors, it is important to: arrange workspace so that the body is not in direct sunlight; and use blinds or shades on the windows during peak sun hours.

Automobile Glass and Photoprotection

In studies of UV exposure in cars, it was shown that the parts of the driver’s and passenger’s bodies closest to the window received the greatest UV exposure. Side and rear windows are usually made from non-laminated glass, allowing a significant amount of UVA to pass through to the passengers in the car. Most windshields are made from laminated glass, the type of glass designed to prevent fragments from shattering onto the occupants during an accident and which can filter both UVB and a large portion of the UVA rays.

Tinting automobile glass is an option that allows 3.8 times less UVA light to be transmitted to the interior of the car as compared to untinted window glass. In a 2004 study of UV transmission and color tint, grey tinted laminated glass provided the highest UV protection with only 0.9 percent of UVA light transmitted versus 62.8 percent transmitted through non-laminated clear glass. People who are considering tinting their windows should take their car to a professional auto detailing shop, in order to ensure that the tinting meets the federally mandated 70 percent of minimum visible light transmittance through the windshield.

“Obviously UVA exposure in a car is influenced by non-glass-related factors such as position of the individual in the vehicle, direction of travel with respect to the sun, and time of day,” stated Dr. Lim. “However, the more time a person spends in a car, especially at the same time of day such as during a regular commute, can greatly affect the amount of UV exposure their skin receives.”

To reduce sun exposure while driving, wear protective clothing, such as a long-sleeved shirt and pants, especially when the body is in the sun; apply sunscreen generously to any exposed skin before driving, especially the hands, forearms and face; and wear protective sunglasses to reduce glare and protect the eyes from UV exposure.

Sunglasses and Photoprotection UV radiation is potentially hazardous to the structure of the eyes, particularly the cornea, lens and retina, which is why the U.S. developed a “sunglass standard,” with the latest version published in 2001. Sunglasses are classified into three categories: cosmetic sunglasses providing minimal UV protection; general purpose sunglasses designed to reduce glare in bright light or when driving; and special purpose sunglasses for activities such as skiing or going to the beach.

“The ideal sunglasses should substantially reduce UV exposure of the cornea and the lens, including any UV coming from lateral directions, and should wrap around the eyes, thereby maximizing eye and eyelid protection,” said Dr. Lim. “For even better protection, wear a broad-brimmed hat which can help reduce the level of UV radiation reaching the eyes and the surrounding area.”

In addition, Dr. Lim recommended the following tips when purchasing sunglasses to maximize UV protection:

Look for neutral gray and amber brown lenses that give true color rendition, particularly to red and green stoplights. Seek glasses with a large frame and lenses that cover the entire eye and wrap around the side of the eye.

Look for the “100% UV Protection” sticker to ensure that the sunglasses meet standards for safe levels of UV protection.

Expensive sunglasses do not necessarily provide better UV protection, according to Dr. Lim. Darkly tinted sunglasses can make pupils dilate and increase lid opening, thereby resulting in increased UV exposure to the lens of the eye.

In addition to wearing sun protective clothing, including sunglasses, you should follow these sun protection tips and Be Sun SmartSM:

Generously apply sunscreen to all exposed skin using a Sun Protection Factor (SPF) of at least 15 that provides broad-spectrum protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays. Re-apply every two hours, even on cloudy days, and after swimming or sweating.

Seek shade when appropriate, remembering that the sun’s rays are strongest between 10 a.m. and 4 p.m.

Use extra caution near water, snow and sand as they reflect the damaging rays of the sun which can increase your chance of sunburn.

Protect children from sun exposure by applying sunscreen. Get vitamin D safely through a healthy diet that includes vitamin supplements. Don’t seek the sun.

Avoid tanning beds. Ultraviolet radiation from the sun and tanning beds causes skin cancer and wrinkling. If you want to look like you’ve been in the sun, consider using a sunless self-tanning product, but continue to use sunscreen with it.

Check your birthday suit on your birthday. If you notice anything changing, growing, or bleeding on your skin, see a dermatologist. Skin cancer is very treatable when caught early.

Photosensitivity : Another Reason for UVA Skin Protection

We react normally to sun exposure by developing a tan or sunburn. But some of us react abnormally from photosensitivity. For instance, during the last two summers, I have broken out in a rash from the sun. My doctor said it is contact dermatitis, preciously, photocontact dermatitis. The allergen could even be a sunscreen ingredient.

UVA is a major trigger for photosensitivity. These rays can penetrate glass, so you’re exposed to UVA when you are near a window or driving your car. UVA penetrates deeper into skin than UVB and can cause premature aging. It can also contribute to skin cancer.

When UV radiation is absorbed by photosensitizer molecules, they in turn elicit a reaction in chromophores, molecules in the skin. The result is an abnormal skin reaction, such as a rash.

Photosensitizers can be either allergens or toxins. Phototoxins can be drugs, plants or coal tar derivatives. They cause sunburn like reactions, and are dose-dependent. Photoallergies elicit immune responses and tend to cause more severe skin reactions. Photoallergens can be drugs or topical agents and can spread beyond the sun exposed region of the skin. These molecules cause a rash like symptom. They are not dose-dependent.

Patients can react to sensitizers that originate outside or inside the body. Various drugs can cause photosensitivity. Cosmetics or other materials may contain potential photosensitizers that are deposited on the skin or given internally, whereas an immune disorder, such as lupus, can cause an abnormal reaction to the sun that originates inside the body.

Some organic sunscreen chemicals absorb UVA, UVB or both. Ingredients, such as octocrylene, protect against UVB. Ingredients, such as avobenzone (Parsol 1780) or a benzophenone (such as dioxybenzone, oxybenzone or sulisobenzone), protect partially against UVA. Some sunscreen ingredients provide physical sun protection that reflect or absorb UVA and/or UVB. These ingredients include zinc oxide and titanium dioxide. Most sunscreens contain a combination of active, as well as inactive ingredients.

“The physical blocking agents have not been reported to cause contact dermatitis, ” writes Daniel More, M.D., in his about.com column and who currently practices allergy and clinical immunology in Salinas, California and is an Assistant Clinical Professor in the Department of Family and Community Medicine at the UCSF School of Medicine. Also, studies have found that inorganic agents, such as zinc oxide, are photostable; they don’t degrade rapidly; however, organic agents tend to be less stable.

“Photostability depends not only on the sunscreen active ingredients but also on the inactive ingredients,” says Susan Cruz, spokesperson for the FDA. “You can compare two different sunscreens with the same active ingredients at the same concentration, and the sunscreens can have different SPF values,” says Susan Cruz, spokesperson for the FDA.

Sunscreen product labels don’t list the percentage of ingredients along with their synonyms. Example: Amyl dimethyl PABA (padimate A, isoamyl-p-N,N-dimethylaminobenzoate, Escalol 506, pentyldimethyl PABA). The FDA limits the percentage of sunscreen active ingredients. For example, zinc oxide is limited to 25%, Avobenzone, 3%.

FDA’s Office of Nonprescription Products within the Center for Drug Evaluation and Research (CDER) is developing UVA testing and labeling requirements for sunscreens. It is currently in final clearance. But in the meantime, avoid the sun between 10 and 4 when UV radiation is more intense, and use sunscreen properly by:

* checking the expiration date.
* applying sunscreen every 2 hours from sunrise to sunset all year round and every hour if you sweat or bathe since sunscreen wears of and loses effectiveness over time.
* applying sunscreen if you are near a window that gets sun or when you’re drying a car. Glass windows don’t block UV-A radiation.
* applying lip balm with broad spectrum sun protection.
* applying sunscreen when you plan to be in the shade since sun light is scattered in all direction, even under an umbrella.
* reapplying sunscreen after rubbing, such as towel drying. Rub the sunscreen in gently or you may rub it off.
* applying evenly a generous amount of sunscreen with broad spectrum sun protection, but don’t rub hard or you may rub it off. About an ounce is required to cover the entire body.

In addition to sunscreen, Cyndi Yag-Howard, M.D., a Florida dermatologist and spokesperson for the Skin Cancer Foundation, recommends that patients at high risk of skin cancer, which includes those who are photosensitive, wear under clothing a broad spectrum sunscreen with an SPF of at least 30, or purchase sun protective clothing that is labeled. And everyone should wear a wide brim hat and sunglasses that filter at least 98% of UV.

FDA wants the labeling on your sunscreen to tell you more about protection against the sun’s harmful rays

Under a new regulation, the agency has proposed that sunscreen labeling be expanded to provide

• A four-star rating system that informs consumers how well the product protects them against “Ultraviolet A” (UVA) light.

• Information on other ways people can limit their risks to dangers posed by overexposure to sunlight.

What do “UVA” and “UVB”stand for?

UVA and UVB are types of ultra­violet (UV) radiation emitted by the sun. Although the atmosphere’s ozone layer shields us from most of this radiation, the UV light that gets through can cause problems. UVB light is primarily responsible for sunburn. UVA light penetrates the skin more than UVB light does, and causes tanning. Both types of UV light contribute to premature skin aging, skin cancer, and other types of skin damage..

Currently, sunscreen labels are required to carry a “Sunburn Protec­tion Factor” (SPF) value that informs potential users how well the product protects against UVB light.

The Four-Star System.

Under the proposed regulation, a UVA star rating would be promi­nently displayed on sunscreen labels, near the SPF rating..

“For more than 30 years, consum­ers have been able to identify the level of UVB protection provided by sunscreens using only sunburn protection factor or SPF values,” said Andrew C. von Eschenbach, M.D., Commissioner, Food and Drugs. Under this proposal, “consumers will also now know the level of UVA protection in sunscreens, which will help them make informed decisions about protecting themselves and their children against the harmful effects of the sun.”

With the proposed UVA rating system.

• One star will represent low UVA protection
• Two stars, medium protection
• Three stars, high protection
• Four stars, the highest UVA protection available in an over-the-counter (OTC) sunscreen product.
• If a sunscreen product does not rate at least one star, FDA is proposing that its labeling bear a “no UVA protection” marking on the front label, near the SPF value.

Sunscreen Not the Only Option.

In addition to the new rating system, FDA wants sunscreen labels to advise consumers that using a sunscreen is just one way they can protect them­selves against the sun. Limiting time in the sun and wearing protective clothing as part of a comprehensive sun protection regimen are other rec­ommendations that would be promi­nently displayed on labels. Using sunscreens liberally and reapplying frequently would also be advised.

Changes With SPFs, Too.

FDA also wants to make changes regarding protection against UVB light. The agency has proposed amending its existing rule on UVB products to increase the maximum sunburn protection factor from SPF 30+ to SPF 50+.

The proposed rule is asking the pub­lic to comment on the use of nanopar­ticle ingredients in sunscreens, and is proposing to

• make minor changes in SPF (UVB) testing procedures consistent with current science, to further enhance the accuracy of SPF values.
• allow new combinations of active ingredients.

More Sun Exposure may be Good for Some People

A new study by scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and colleagues in Norway suggests that the benefits of moderately increased exposure to sunlight – namely the production of vitamin D, which protects against the lethal effects of many forms of cancer and other diseases – may outweigh the risk of developing skin cancer in populations deficient in vitamin D.

“We know that solar radiation is the leading cause of skin cancer,” said communicating author Richard Setlow, a Senior Biophysicist Emeritus at Brookhaven and a well-known expert on the link between solar radiation and skin cancer. Setlow’s group was the first to establish that ultraviolet A (UVA) radiation and visible light are the primary causes of malignant melanoma, the deadliest form of skin cancer. He and his colleagues emphasize that people need to protect themselves from the harmful effects of sun exposure.

But solar radiation is also a major, if not the main, source of vitamin D in humans. In the presence of sunlight, the body converts certain precursor chemicals to active vitamin D.

“Since vitamin D has been shown to play a protective role in a number of internal cancers and possibly a range of other diseases, it is important to study the relative risks to determine whether advice to avoid sun exposure may be causing more harm than good in some populations.” The concern, he says, is particularly great in populations from northern latitudes, such as Scandinavia, where sun exposure is extremely limited.

In the current study, Setlow and his colleagues used a model incorporating information on solar radiation intensity and a vertical cylinder shape to represent the human body’s skin surface to calculate the relative production of vitamin D via sunlight as a function of latitude, or distance from the equator. The cylindrical model more realistically represents human body sun exposure than flat surface exposure measurements used in previous models. The scientists also examined the incidence of and survival rates for various forms of cancer by latitude.

According to the calculations, people residing in Australia (just below the equator) produce 3.4 times more vitamin D as a result of sun exposure than people in the United Kingdom, and 4.8 times more than people in Scandinavia.

“There is a clear north-south gradient in vitamin D production,” Setlow says, “with people in the northern latitudes producing significantly less than people nearer the equator.”

In populations with similar skin types, there is also a clear increase in the incidence of all forms of skin cancer from north to south. “This gradient in skin cancer rates indicates that there is a true north-south gradient in real sun exposure,” Setlow says.

The scientists also found that the incidence rates of major internal cancers such as colon cancer, lung cancer, and cancers of the breast and prostate also increased from north to south. However, when the scientists examined the survival rates for these cancers, they found that people from the southern latitudes were significantly less likely to die from these internal cancers than people in the north.

“In previous work, we have shown that survival rates for these cancers improve when the diagnosis coincides with the season of maximum sun exposure, indicating a positive role for sun-induced vitamin D in prognosis – or at least that a good vitamin-D status is advantageous when combined with standard cancer therapies,” Setlow says. “The current data provide a further indication of the beneficial role of sun-induced vitamin D for cancer prognosis.”

So, how can people get the benefits of vitamin D without running the risk of deadly skin cancer”

“As far as skin cancer goes, we need to be most worried about melanoma, a serious disease with significant mortality,” Setlow says.

Melanoma is triggered by UVA (the long UV wavelengths) and visible light. Vitamin-D production in the body, on the other hand, is triggered by UVB (the short UV wavelengths at the earth’s surface). “So perhaps we should redesign sunscreens so they don’t screen out as much UVB while still protecting us from the melanoma-inducing UVA and visible light,” Setlow says.

Increased UVB exposure may result in an increase in non-melanoma skin cancers. But these are relatively easy to cure and have very low mortality rates compared with the internal cancers vitamin D appears to protect against, Setlow adds.

Another option would be to increase vitamin D consumption while continuing to wear sunscreen. Vitamin D is easily accessible in many foods and liquids, such as cod liver oil and milk, and in dietary supplements.