Understanding SPF and How To Protect Your Skin
P. Travis Harker, MD
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Most Americans know the risks of not protecting their skin from too much exposure to ultraviolet radiation from the sun. Sunlight consists of two types of harmful rays, ultraviolet A rays (UVA) and ultraviolet (UVB) rays. Too many UVA or UVB rays can cause skin cancer. In addition, UVA rays prematurely age skin, and cause wrinkles and age spots. UVB rays are the main cause of sunburn. UV radiation from the sun, as well as from tanning beds and sun lamps are listed as carcinogens, or cancer-causing substances, by the World Health Organization. Avoiding artificial UV rays is easy, but decreasing exposure to the sun's radiation takes a bit more work. Many medical organizations, including the American Cancer Society, recommend wearing protective clothing, a hat, and sunscreen when you will be in strong sunlight. With thousands of sunscreens on the market, it is important to know how to choose the right one.
The U.S. Food and Drug Administration (FDA) regulate sunscreen products as over-the-counter drugs, and they require that all sunscreens retain their original strength for at least three years. Sun Protection Factor, or SPF, measures how effectively a sunscreen can help prevent skin damage from ultraviolet radiation. 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.
Broad spectrum sunscreens are best at helping block both UVA and UVB rays. The American Academy of Dermatologists (AAD) recommends using a broad spectrum sunscreen “with a SPF of at least 30, which blocks 97 percent of the sun's UVB rays. Higher-number SPFs block slightly more of the sun's UVB rays, but no sunscreen can block 100 percent of the sun's UVB rays. It is also important to remember that high-number SPFs last the same amount of time as low-number SPFs. A high-number SPF does not allow you to spend additional time outdoors without reapplication. All sunscreens should be applied approximately every two hours or according to time on the label, even on cloudy days, and after swimming or sweating.”
Who Needs Sunscreen?
Those with certain risk factors need to be especially diligent in applying sunscreen. These include having:
- Fair skin
- Blonde or red hair
- Blue, gray, or green eyes
- A history of sunburns early in life
- A history of indoor tanning
- Many moles and freckles
- Family or personal history of skin cancer
Anyone can get skin cancer, though, even those with darker skin. Greater amounts of melanin in the skin provide natural protection, but family history, ethnicity, and skin cancers that are not caused by UV exposure can still put darker-skinned people at risk. For example, darker-skinned people are more likely to get a type of skin cancer that affects the palms of the hands and soles of the feet.
In addition, UV radiation exposure also is increased by other factors, including:
- Snow - Sun reflected on snow can produce as much ultraviolet penetration as the sun on sand, especially at higher altitudes. Snowboarders and skiers need adequate protection on exposed areas, regardless of the temperature.
- Wind - Wind can thin sunblock, so make sure to reapply every 2 hours or so if you are in a windy environment (think beaches, skiing, and sailing).
- Clouds and Haze - Cloudy days are no excuse to skip the sunblock. About 80% of the sun's rays still get through.
- Water - Water is not a good filter. You can become sunburned while swimming or snorkeling.
- Latitude - The closer you are to the equator, the more harmful the sun's rays are.
- Altitude - UV radiation increases nearly 4% every 1,000 feet above sea level you go.
- Reflection - Sand, concrete, water, and snow are highly reflective surfaces that can expose you to more of the sun's rays.
Applying Sunscreen and Keeping It On
It is important to know which sunscreen to purchase for your skin type and your activity level, as well as the correct way to apply it. Some tips include:
- Apply it early. Apply sunscreen 20 minutes before any sun exposure so that it has time to chemically react with the skin.
- Choose water-resistant formulas. Sport formulas are usually water-resistant, easy to apply, will not drip into the eyes, and will not interfere with a grip on a tennis racket or a golf club.
- Do not be stingy. It should take about 1 ounce, or a shot glass-worth, of sunblock to cover your whole body.
- Reapply. If you are walking or doing a low-intensity activity, reapply sunblock at least every 2 hours. If you are sweating profusely, or are in the water or a windy area, apply it more frequently.
Other Sun Savvy Solutions
In addition to understanding SPF and how to choose an appropriate sunscreen, there are other ways to help protect your skin from sun damage:
- Avoid the sun between 10 am and 2 pm. The sun's rays are at their worst during these hours. Exercise in the early morning or later in the day—a time when it also is cooler. If lunchtime is the only time you can work out, seek out a shady route, load up on the sunscreen, and keep it brief.
- Use a broad-spectrum sunscreen. Find one that blocks both UVA and UVB rays, with a SPF of 30 or higher.
- Wear a broad-brimmed hat. Baseball hats leave cancer-prone areas such as ears and the back of the neck exposed. A smarter option is a hat with at least a 2- to 3-inch brim. If you have thinning hair, or are bald, a hat is a must.
- Wear long sleeves and long pants when possible. Look for clothes with tightly woven material. When you apply sunblock, you should still apply it on areas that will be covered by clothing. A typical T-shirt has an SPF rating lower than 15. There is clothing, like swimming rash guards,that are made to have higher SPF ratings.
- Protect your ears, nose, cheeks, and hands. Since the majority of skin cancers occur on these areas, consider them a top priority.
- Don't skip the lips. Skin cancer also can occur on the lips. Look for a waterproof or water-resistant, lip-specific product with a high SPF. Plan on reapplying often as lips are moist and lip balms have a tendency to wear off easily.
- Wear sunglasses. Choose sunglasses with UV protection. This will also protect the delicate skin around the eyes.
Choosing to protect your skin by taking precautions like wearing sunscreen may not only keep you looking younger, but may save your life. As Mahatma Gandhi put it, “The future depends on what you do today.”
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