The long answer, though: That shouldn't matter. By that I mean companies such as Columbia and Sun Precautions test their sun-protective clothing through repeated washings and exposure to sunny conditions. In the case of something such as Columbia's Silver Ridge Shirt ($40; www.columbiasportswear.com), it's put through the equivalent of 40 machine washings and 100 days of sun exposure. Columbia's fabric itself is sun-resistantsome other makers either weave in sun-proofing fabrics (which reflect UV rays) or coat their fabric with UV-resistant chemicals. Nothing wrong with that, it's just a different way to do things.
Even with sun-resistant clothing, it's still prudent to use a sunscreen if sun exposure is a real issue for you. Most sunscreens with an SPF rating of 15 to 20 are fine for all but the most sun-sensitiveanything more than that is really gilding the lily. I've had good success with many sunscreens, but like Aloe Gator Super Waterproof Sunblock Lotion SPF 15 ($4.95 for three ounces; www.aloegatorsuncare.com).