April 21, 2004 (STAR) AN APPLE A DAY By Tyrone M. Reyes, M.D. - It’s summer and people are heading for the beach, the lake, or the pool. And virtually everyone knows by now that it’s a good idea to slather on a sunscreen to protect against sunburn that can lead later in life to photoaging and skin cancer. And there is no doubt that by blocking sunlight, sunscreens protect against damage to your skin.

But do you know how the sun burns your skin and how sunscreens protect you? And what’s the ideal sunscreen for you to use against our hot tropical sun? Uva And Uvb

The light spectrum is organized by wavelength. UVA is light with a wavelength that is longer than UVB but shorter than what can be seen by the human eye. UVA was long thought to be a harmless, tan-producing part of the spectrum. Because it has a longer wavelength, UVA does penetrate deeper into the skin than UVB. But UVA is less energetic than UVB and plays a smaller part in sunburn. In fact, earlier generations of sunscreens were designed specifically to let UVA through. Sunlamps and tanning beds use mainly UVA, although sunlamps that also emit some UVB are believed to produce a better tan. Now, it is known that UVA damages and ages the skin in a wide variety of ways by initiating a molecular cascade that produces reactive forms of oxygen that damage DNA and cell membranes. UVA may also suppress the immune system. And some researchers believe it is predominantly UVA exposure that causes malignant melanoma, the most dangerous form of skin cancer.

Many, if not most, of the products now for sale are "broad spectrum" and claim to protect against not only UVB but also UVA. Sunscreens are made UVA-protective in two ways. Manufacturers add a chemical that absorbs UVA light, the most common of which is oxybenzone, or they add very finely ground zinc oxide or titanium dioxide. Many sunscreen makers do both. Zinc oxide and titanium dioxide are good UVA protectors, but there is disagreement about how protective titanium dioxide is in the transparent sunscreens that most people like.

How The Sun Burns

UVB is primarily responsible for the sun’s acute and obvious sunburning effects on your skin. UVA can also cause sunburn but to a much lesser extent than UVB. Ultraviolet rays from the sun penetrate your skin. At first, exposure to sunlight causes erythema, a dilatation or widening of small blood vessels. This leads to an increase in the volume of blood flowing to your skin, which accounts for its initial red glow.

The amount of sun exposure you can tolerate before your skin turns red depends on several factors. Virtually everyone is susceptible, to some degree, to the sun’s ultraviolet rays. Your natural skin type, determined by the amount of melanin or skin pigment, is the major determining factor.

As ultraviolet radiation penetrates the surface of your skin, cells several layers down increase melanin production. The pigment then migrates to and darkens the uppermost layers of your skin. This tan appears two to three days after you were in the sun and lasts several weeks to months, depending on how often you continue to be exposed to the sun.

The darker your complexion, the more the melanin, and the faster tanning appears and the longer it lasts. Nonetheless, a tan at most gives an SPF of only 3. Thus, even us Asians with brown skin can burn with sufficient exposure to the sun.

How Sunscreens Protect

Sunscreens work by either absorbing ultraviolet radiation or by physically blocking it from ever reaching your skin. Most sunscreens protect against both UVB and UVA radiation. Most sunscreen ingredients absorb UVB radiation. Only two or three are UVA absorbers. The protection against UVA in sunscreens is primarily due to the physical barrier rather than the chemical effects offered by the sunblocks.

A sunscreen’s effectiveness depends on the amount of protective chemicals it contains. Sun protection products are labeled according to their degree of effectiveness with a "sun protection factor" or SPF. The SPF is simply a multiple of the time it takes the sun to turn your skin red. For example, if you can stay in the sun unprotected for only 10 minutes before suffering sunburn, an SPF—15 sunscreen will protect you for up to about 150 minutes (10 x 15).

Increasing the number and concentration of chemicals in the sunscreen increases the SPF. Depending on the chemical makeup, sunscreen products have an SPF that ranges from 2 to 50.

The Ideal Sunscreen

Most people have been told that they should use a sunscreen with an SPF of at least 15 or higher. That was the recommendation of the American Academy of Dermatology in 2000. The guideline, however, was primarily for Americans with white skin, living in the mid— and higher latitudes. Furthermore, the studies that were used to base such recommendation were done in laboratories using artificial light. Would it therefore also hold true in Filipinos who have a different colored skin and are exposed to the hot tropical sun?

The eminent Filipino dermatologist, Dr. Vermen Verallo—Rowell, had been doing studies on how sunscreen ought to be used in the tropics since the 1970s. In her now classic book, Skin in the Tropics, Sunscreens and Hyperpigmentation (Anvil Publishing, 2001), Dr. Verallo-Rowell mentions that "the ideal broad-spectrum sunscreen, better known as sunblock, to use in the tropics should contain ingredients that are specifically anti-UVB, UVA, VL (visible light) and IR (infrared light)…. These are sunscreens, usually with SPF 30 or higher, with anti-UVA ingredients, and with titanium dioxide, zinc and iron oxide physical light blocks."

Furthermore, it "should also contain an acrylate ingredient for sweat and water proofing; be in an emulsion-type base for optimal spread and absorption; be free of perfume and masking scents; and be preserved only with parabens or similar low-sensitizing preservatives."

Tips For Using Sunscreen

Here are some tips to get the most benefit from sunscreen products:

• Always use a sunscreen if you have sensitive skin ("burns easily"), suffer allergic reactions to the sun, or are exposed to the sun on a regular basis.

• Use sunscreen even on cloudy or hazy days. Burning rays can penetrate cloud cover.

• Remember: To achieve the SPF advertised on any sunscreen, apply the product liberally on the face and other exposed areas of the body. Don’t forget your ears, the back of your neck and, if you’re balding, the top of your head.

• Apply a sunscreen at least 15 minutes before going outside, to allow the protective chemicals to be absorbed into your skin. Reapply once or twice if you remain outdoors. You should reapply even waterproof sun protection products after you swim, when you dry yourself off with a towel, or wipe the perspiration from your brow.

• Keep infants under six months of age out of direct sunlight and in the shade. Sunscreen should be applied beyond six months of age. In fact, the US FDA specifically recommends that sunscreens that contain para-aminobenzoic acid (PABA) should not be used on infants younger than six months because they may become allergic to these. Encourage children to use sunscreen each time they go outside. The cumulative effects of unprotected sun exposure over many years weaken the skin’s elasticity, leading to sagging cheeks, deeper facial wrinkles and skin discoloration later in life.

• You may apply makeup over sunscreen. Sunscreens used under makeup are still effective.

• If possible, try to avoid being exposed to the sun from noon to 2 p.m., when the sun’s rays are most intense.

Finally, remember that hats with a four-inch brim and other clothing protect best against the sun. And, because of the risk of skin cancer, deep, dark tans are no longer in vogue!

Reported by: Sol Jose Vanzi

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