Conventional wisdom used to be that rubbing sunblock on exposed skin offers protection from ultraviolet radiation. Clothing, on the other hand, only partially blocks sunlight, leaving a lot of skin at risk.

Conventional wisdom used to be that rubbing sunblock on exposed skin offers protection from ultraviolet radiation. Clothing, on the other hand, only partially blocks sunlight, leaving a lot of skin at risk.

In the past few years, clothing has begun to sport an "Ultraviolet Radiation Protective Factor" — UPF — rating, much like the SPF factor used to rate sunscreens and sunblock. Ultraviolet light is not visible to the eye, but its effects are visible as sunburn and skin cancer.

While most people would not cover themselves with a fishnet shirt in the heat of summer, more conventional shirts also feature woven construction, albeit with much smaller holes between the threads.

"Natural fabrics, as in cottons, hemps, bamboos — they are natural, but you can't get a fine enough weave in the fiber to stop the void spaces between the weave that allow the sun to go through," says Robbin Lacy, co-founder with his wife, Angeline, of Sunday Afternoons, a Talent-based clothing company that is a nationwide leader in the design and distribution of sun-protective clothing.

"We found synthetics — primarily nylons and polyester — to be fine enough that the mechanical weave will actually stop a big amount of UVA and UVB that theoretically could penetrate," explains Lacy.

UVA and UVB are the two types of ultraviolet light from the sun that reach the earth's surface.

In addition to reducing the space for light to penetrate the clothing, dyes and other chemical processes that molecularly bond to the fabric are key in the manufacture of sun-protective clothing.

"The chemical finish creates a diffusing effect, so that even though one may see pinholes of light going through fabric when you hold the fabric up to the sun, the UV is not going through," says Lacy.

The less ultraviolet light that penetrates the clothing, the higher the UPF rating. The highest rating is "UPF 50+," meaning that less than 1/50th or 2 percent of UV light passes through clothing onto skin.

Sunday Afternoons had its birth in the early 1990s making picnic blankets — the company name is a reference to the most popular time for a picnic. The blankets were sold primarily at arts-and-crafts fairs. When the Lacys decided to give away hats with the purchase of their blankets, they found the hats to be more popular, especially with an aging population.

"That retail customer is a 40-plus demographic. Young people are still invincible when it comes to the sun," says Lacy, with a laugh. "When you're 40 and above, that's when sun exposure reveals its cumulative, lovely self on your skin."

More than 2 million people in the U.S. are diagnosed with skin cancer annually, according to the American Academy of Dermatology, and one in five will develop skin cancer over the course of his or her lifetime.

Dermatologists use the term "photoaging" to describe premature aging of the skin due to repeated sun exposure. This exposure results in damage that includes freckles, wrinkles, spider veins on the face, rough and leathery skin, loose skin and a blotchy complexion.

Although the Lacys are developing high-UPF trousers and skirts, their focus is still hats. Their current direction is sport-specific headgear.

"Last year, we came out with a hat designed for stand-up paddling, surfing, water-skiing, things that you can wear right in the water," explains Lacy. "We have one with a reinforced brim that never gets in your eyes even if you wipe out surfing."

This hat was tested successfully by windsurfers in Hood River. Lacy is a surfer from way back, so he's attuned to the extra damage the skin takes in water.

"You get charred when you're out surfing. There's no shade out there, and sunscreen you have to apply every 1 1/2 to 2 hours, and they don't last — nobody does that," says Lacy. "I'm an Irishman, so I'm a magnet for UV. Having had many terrible sunburns in my life, I'm beginning to see pre-skin cancer (signs)."

Because of this past exposure to the sun, Lacy says he now sees sunburn differently.

"People think of the sunburn as the result of something simply hot and firelike from the sun," he says. "But when you get a sunburn, it's actually a radiation burn from the sun's nuclear reaction."