JANE E. BRODY
Are all sunscreen ingredients equally effective? And equally safe? How high an SPF should one choose? Is SPF 60 really that much better than SPF 30? What does broad spectrum mean?
And perhaps the most frightening question: Why has the incidence of melanoma,the deadliest of skin cancers,doubled since sunscreens (as opposed to tanning lotions) became popular?
No better time to get the answers to these questions than now as summer sun beats down on you.
First,some facts about sun and current sunscreen labels. There are two kinds of solar rays: short ones called UVB that cause burning and skin cancer and long ones called UVA that cause skin cancer and wrinkling. SPF ratings the letters stand for sun protection factor reflect only the extent of protection against UVB. The higher the rating,the longer one can stay in the sun before burning.
But there are two important caveats. First,SPF ratings are based on a rather thick application of sunscreen,not the amount consumers normally use,which is most often a quarter to a half the amount applied in manufacturers tests. An adult in a bathing suit should apply about three tablespoons of lotion every two hours,experts say.
Second,above an SPF of 30,which can block 97 per cent of UVB (if used in testing amounts),effectiveness increases by only 1 or 2 per cent. In the way that sunscreens are used in the real world,then,a product with an SPF of 30 actually provides the protection of SPF 2.3 to 5.5,and one rated SPF 50 provides the protection of SPF 2.7 to 7.1,according to a report published in Drug and Therapeutics Bulletin.
UVA,which represents more than 95 per cent of solar radiation reaching the earth,does not figure in SPF ratings. The phrase broad spectrum is meant to indicate protection against UVA,but there is no numerical rating for product effectiveness.
Dermatologists suggest choosing only products that are labeled broad spectrum and have an SPF rating of 30 to 50. There is no evidence that anything higher than 50 is any better. Apply the sunscreen just before exposure,and reapply it two hours later – it loses effectiveness over time. And even if the label claims the sunscreen is water resistant,be sure to reapply it after swimming or sweating heavily.
The rise in melanoma has led to fears that sunscreens may actually cause this deadly cancer. But other explanations are more likely. By allowing people to stay in the sun longer,sunscreens have greatly increased exposure to UVA radiation. And many,if not most,victims of melanoma were damaged long before sunscreens became popular. A history of sunburn is a major risk factor for this cancer; five sunburns per decade raise the risk by about threefold.
Another reason for the increase in diagnoses: skin cancer screening and detection have improved greatly in recent decades.
With regard to ingredients,many dermatologists recommend products with micronized titanium or zinc oxide as the most effective sun blockers that leave no white residue on the skin. There is some concern,based on animal studies,that the most popular ingredient in sunscreens,oxybenzone,may disrupt natural hormones,but the scientific evidence is scant.
Another chemical,retinyl palmitate,sometimes listed among the inactive ingredients,has been linked to skin cancers in animal studies.
Because it is converted into a compound that can cause birth defects,it should be avoided by women who are pregnant or likely to become pregnant.
However,although more studies of these possible risks should be done,Consumer Reports concluded that the proven benefits of sunscreen outweigh any potential risks.
Seek other protection
The best advice to prevent UV damage is to stay out of the midday sun altogether and to cover up with clothing,a hat and umbrella during the rest of the day even if it is cloudy. Clouds do not block damaging rays.
Keep in mind that UV radiation is reflected off sand and water,intensifying exposure even if you are protected by an umbrella from above.
Ordinary clothing provides a good sun shield when dry (the tighter the weave,the better) but little or no protection when wet. Special sun-protective clothing is costly but works well wet or dry; it is a wise investment for children who tend to stay in or around water for hours. And no matter how well covered up you are,dont forget to apply sunscreen to your face,ears,neck and hands.
Also,keep in mind that some sun exposure is necessary to maintain a healthful level of Vitamin D.