Dear Doctor Column, June 15, 2009

Question:

This year I see sunscreens with SPF 100. Do the high SPF numbers work better than the lower ones?

Answer:

Sunscreens absorb, reflect, and scatter UV light. SPF, or sun protection factor, is often misunderstood. SPF indicates protection from UVB rays only. SPF numbers are an estimate of how long you can stay in the sun before burning compared with not using sunscreen. For example, if you’re fair-skinned and normally begin burning after 10 minutes, properly applying an SPF 15 sunscreen would, theoretically, allow you to stay in the sun 150 minutes without burning. The American Cancer Society recommends always using a sunscreen with an SPF of 15 or higher. 

The higher SPF sunscreens offer slightly better protection, but not enough to merit a higher price. SPF 15 protects against 93% of UVB rays, an SPF 30 protects you from 97%, SPF 50 products shield 98% of UVB radiation. SPF 100 bumps that to 99%.

No sunscreen can completely block the sun’s rays. Look for sunscreen with at least SPF 15 or SPF 30 that offers protection from both UVA and UVB rays. The proliferation of sunscreen products with higher and higher SPFs has led the FDA to develop a rating system for sunscreens, and FDA is planning to limit SPF claims to 50+ by the end of the year. The agency may also expand labeling to provide a star rating system to inform consumers how well the product protects against UAB light, though it will be about a year before packaging on the store shelves changes.

Some ingredients offer more comprehensive protection than others. Active ingredients in sunscreen are usually one of two types: organic chemicals that absorb UV radiation (while organic agents protect you from UVB rays, most can’t shield you from UVA radiation) and physical sunscreens that absorb and reflect UVA and UVB rays away from the skin.

Physical sunscreens are made from metal oxides, such as zinc oxide and titanium dioxide, or particulate UV filters. Physical sunscreens offer the most protection from the sun but often are visible on the skin; some come in micronized and skin-colored formulations that are more subtle in appearance but also may be less effective.

 There is no accepted system for measuring UVA protection, so you can’t rely on sunscreen labels that promise “broad-spectrum UVA/UVB” protection – you need to read through the ingredient list.

 Look for products that list at least three active ingredients, which is the minimum number for broad-spectrum protection. Sunscreens with four or more ingredients typically contain a physical sunscreen and offer more protection. Active ingredients include:

• avobenzone (also called Parsol 1789)
• benzophenones (also called oxybezone)
• cinnamates (also called octinoxate, cinoxate)
• ecamsule (also called Mexoryl Sx)
• physical sunscreens such as zinc oxide or titanium dioxide

 Keep in mind that individuals with sensitive skin may experience skin rash and allergic photosensitivities irritation with chemical sunscreen ingredients such as aminobenzoic acid and its esters (PABA), cinnamates, and oxybenzone.

Proper Application Is Key

Apply a generous amount – about an ounce (2 tablespoons), or palmful, to cover an average-size adult body — and reapply the same amount at least every 2 hours or after swimming or sweating. Most important is to apply enough and to reapply every two hours use an ounce of product. So, if your sunscreen bottle is only 8 ounces, you should get about 8 applications from that one bottle.

 To reap the protective benefits of any sunscreen, you need to apply it about 30 minutes before going out in the sun. This gives your skin a chance to absorb sun-shielding agents.

 Most people use too little sunscreen and don’t reapply often enough. Research indicates people generally apply only about half the amount of sunscreen the Food and Drug Administration uses in assigning SPF numbers. If you apply only a thin film, you have less protection, perhaps an SPF of about 2 against UVB rays. If you normally start turning red in 10 minutes, an SPF of 2 would deflect 50% of UVB rays for only 20 minutes before you begin to burn.

 Labels that say “water resistant” or “waterproof” also are misleading. All sunscreens lose their effectiveness when immersed in water – some just last longer than others. Sunscreens labeled “water resistant” will protect you for about 40 minutes of water exposure, while those labeled “very water resistant” or “waterproof” offer about 80 minutes of protection. Regardless of the label, reapply sunscreen after taking a swim or sweating heavily.

 And don’t forget your children. On average, children get 3 times more sun exposure than adults. Regularly using sunscreens with an SPF of 15 or higher and physical sunscreen ingredients through age 18 can substantially lower the risk of certain types of skin cancer.

Infants, who have thinner, more easily damaged skin, need special protection. Avoid sun exposure when possible and when your baby is in the sun use hats, clothing, and umbrellas or sun canopies to protect their skin. There has been some controversy about the safety of sunscreen for infants younger than 6 months. The American Academy of Dermatology now says chemical-free sunscreens — those made from titanium oxide or micronized zinc oxide — are safe for infants and can be used on areas of the skin not protected by clothing.

 Just one bad blistering sunburn in childhood can double the risk of skin cancer later in life. By age 65 years, an estimated 20% to 25% of Americans will have at least one episode of skin cancer. UAB dermatologists and the American Academy of Dermatology stress the best policy is avoiding sunbathing and unprotected exposure to the sun. They also recommend:

• Wearing a physical sunscreen when outside that protects against UVB and UVA rays and covering up with long sleeves, long pants, and a wide-brimmed hat.
• Avoiding prolonged outdoor activity when the sun is at its peak - 10 am to 4 pm.
• Protecting your skin from the sun on cloudy days since the sun’s rays penetrate light clouds, mist, and fog.
• Always adding sunscreen to your ears, nose, neck, hands, and to your scalp where it is exposed by the part in your hair. These areas are easily overlooked but are prone to bad burns.
• Applying sunscreen even when you’re under a beach umbrella. UV rays reflect off the sand and damage your skin. That goes for concrete, snow, water, and other reflective surfaces.

 Many people love a tanned look, but the only safe tan is one produced with a self-tanner. UAB dermatologists recommend getting a sun-kissed glow from a bottle and note that newer formulations of sunless tanners avoid the orangey skin tone and streaky results of some older products. Sunless tanners, available as lotions, creams and spray-ons, don’t cause skin cancer, wrinkles, or other sun damage, but nor do they protect you from UV rays — no matter how dark you get using these products, you’ll still need to apply a sunscreen to avoid skin damage.

 Protecting your skin from the sun’s rays will reduce your chances of developing skin cancer and stave off premature aging.