You may have come across workout clothing that claims to have "UPF" technology in it. UPF stands for "ultraviolet protective factor," and you can think of it as SPF for clothing, because it means that you'll get extra protection from ultraviolet rays when wearing it, says Shari Lipner, MD, PhD, assistant professor of dermatology at Weill Cornell Medicine. "UPF clothing is manufactured and tested to protect your skin from UV rays," she says.
Technically, clothing doesn't have to be labeled "UPF" to protect your skin from the sun, Dr. Lipner says. An item's UPF rating is simply an indicator of how well it blocks UV rays. The fabric on high-UPF clothing tends to be structured with a high fiber density, so it's harder for light to penetrate it, she says. Or, it could mean that the fabric is pre-treated with ingredients that inhibit UV light.
Having UPF clothing can make a difference when you're outside all day in the sun. For example, a plain white t-shirt would have a UPF between 5-8, meaning 20% of UV rays would penetrate the clothes, Dr. Lipner says. But anything with a UPF of 50 and higher would only let 2% of rays in, so that's the rating Dr. Lipner suggests looking for. However, you still have to wear sunscreen to protect the exposed areas of skin, she says.