Ever since I was old enough to feel self-conscious about my sun-dappled nose, I have been secretly envious of Mediterranean types with their olive complexions and easy tans. The grass is always greener - and the skin always better - on the other side. Thanks to my Irish heritage, I have fair skin that freckles and burns at the first glimpse of sunlight. In fact, my skin sports patches of faint freckles on areas of my body that I don’t remember ever exposing to the sun. Little did I know that wearing clothes does not count as protection from the sun’s damaging rays.

Of course, heading outside clothed is better than wearing your birthday suit, but not all clothing is created equal. A regular cotton T-shirt generally allows up to 50% of UV rays to penetrate to your skin. That figure jumps to 70% when said T-shirt is wet. As you might expect, denser fabrics like denim provide more sun protection than lightweight materials like linen. A long-sleeved dark jean jacket amounts to fail-safe, sun-proof armor. The color and weight of the fabric, tightness of the weave, and coverage of skin all factor into how well the skin is guarded from sun damage. The type of fabric is also important; high-luster polyester and satiny silk naturally reflect radiation, whereas unbleached cotton contains pigments called lignins that absorb radiation.

In Australia, home of the world’s highest incidence of skin cancer, the government developed a rating system in 1994 to gauge a product’s effectiveness in shielding skin from UV rays. Called the UPF, or Ultraviolet Protection Factor, this measurement indicates how much of the sun’s UV radiation penetrates a fabric and reaches the skin. Based on the Australian model, a U.S. standard was formally established in 2001, along with a testing process that uses a radiation-measuring device to collect the UV light transmitted through a garment’s fabric. Clothing manufacturers have voluntarily adopted this system, though some still maintain the SPF labeling system, such as Sunsibility’s gloves.

Like SPF (Sun Protection Factor), that far more common UV-protection measurement slapped on every bottle of sunscreen, a higher rating equals a greater degree of protection. UPF differs from SPF in that SPF calculates the amount of time it takes for sun-exposed skin to redden while UPF calculates the amount of UV light absorbed by a fabric. Another difference is that UPF measures a garment’s effectiveness against both UVA and UVB light. An SPF rating refers exclusively to sunburn-inflicting UVB rays.

A piece of clothing with a UPF rating of 50 will permit only 1/50th (or 2%) of the sun’s UV rays to pass through to the skin; a garment rated UPF 25 will permit roughly 1/25th (4%) UV transmission, and so on. Based on the level of sun protection, a rating of 15-24 is considered “good,” 25-39 is “very good,” and over 40 is “excellent.” Only clothes with a UPF between 15 and 50 may be marketed as sun-protective, and the rating must be higher than 30 to receive The Skin Cancer Foundation’s Seal of Recommendation.

I had never given “sun-protective” apparel much thought until I walked into UNIQLO this past weekend. Everywhere I turned in the store, there were signs touting UNIQLO’s newly developed UV Cut collection, which includes women’s tanks, blouses, stretchy shirts, cardigans, and hoodies. I carried an armful of basic pieces to the dressing room and was duly impressed with their soft texture, good fit, and range of colors, cuts, and fabrics. Each piece in the collection was designed to filter 90% of UV rays.

As an added sun-protective touch, many of the long-sleeved items feature handy finger holes. At first this design - sometimes seen on winter-weather clothing to protect hands from the cold - struck me as bizarre on a summer-weight piece. But then I remembered Sunil’s article about how thin and vulnerable the hands are. The backs of the hands are probably the most neglected and exposed part on the body. They are bombarded by the sun’s rays while driving, walking outside, and doing just about any warm-weather activity. UNIQLO's UV collection is both functional and fashionable.

But what if your clothes don’t explicitly state a UPF? Though there are exceptions, a good rule of thumb for determining the UPF of an item of clothing is to hold it up to visible light. If you can see through it completely, the UPF is probably under 15, which is hardly adequate protection for a long period of time under the sun. So, a sheer swimsuit cover-up won’t ward off sunburn after hours at the beach. If you hold up a piece of clothing and you can’t see through it but a little light peeks through the fibers, then the UPF falls somewhere between 15 and 50, depending on how dark and tightly-woven the fabric is. Keep in mind that wetting an article of clothing reduces its sun protection by up to half.

Apparently, my mother was unaware of this phenomenon when she forced me to wear a white T-shirt over my bathing suit every time I went swimming throughout my childhood in Florida. Not only is a white cotton shirt pretty powerless against the sun, but a wet white shirt is even weaker. After getting soaked and becoming nearly transparent, a T-shirt’s UPF can fall from about a 6 to only a 3. The same loss of protective ability can be said for fabrics that become stretched or worn out.

The moral of the story is that you can’t count on light-colored, lightweight, or loosely-constructed clothes to block out damaging rays, unless these clothes have been specially treated with chemical UV absorbers or sunblocks to prevent penetration of the sun’s damaging rays. Apart from buying a brand-new wardrobe of high-tech, sun-shielding apparel, what can you do to keep your skin safe? If you’re going to be out in the sun for a long time, your best option is to apply a broad-spectrum sunscreen all over your body, including areas covered up by clothes. You can also enhance the everyday sun protection of your garments by washing them in a laundry additive like Sun Guard, which contains the sunscreen Tinosorb. This added protection is supposed to survive twenty washings.

I was so excited about the UV Cut line at UNIQLO that I snatched up six pieces enhanced with the sun-shielding technology. Not all of the pieces offer the same degree of defense. Some bear a UPF of 50, while others are labeled a mere UPF 10, barely better than a standard cotton shirt. But UNIQLO is on the right track, and I will feel safer under the sun this summer wearing my new purchases. My freckled skin will take all the help it can get in the sun protection department.