7 things to know about UPF, sun protection and clothing

Protecting our skin from harmful ultraviolet (UV) light is a year-round job. It requires wearing the proper clothing, using sunscreen on exposed skin, and seeking shade when the sun’s rays are at their strongest. 

But have you ever wondered what distinguishes regular, everyday clothing from the kind you see advertised as having a UPF, or Ultraviolet Protection Factor? Or, the difference between UPF and SPF, which is listed on bottles of sunscreen and other skin care products?

For answers to these and five other questions, we went to dermatologist Valencia Thomas, M.D., who serves as director of MD Anderson’s Mohs Center. Here’s what she shared with us.

What’s the difference between SPF and UPF?

• SPF, or Sun Protection Factor, is based on the amount of time it takes for skin to start turning red after being exposed to UV light. The number indicates how many times longer than that a product applied to the skin might protect you, if used properly. So, if you’d normally start to burn after about 10 minutes out in the sun, sunscreen with SPF 30 could theoretically extend that period by 30 times — or for up to five hours (300 minutes).
• UPF, or Ultraviolet Protection Factor, meanwhile, is a measurement of the amount of UV light that can reach your skin through a particular fabric. The number here represents the bottom part (denominator) of a fraction. So, if a bucket hat is advertised as having UPF 50+ protection, that means only about 1/50^th of the sun’s UV rays — or 2% — can pass through it.

Another difference is that UPF blocks both UVA and UVB light. Unless a product is labeled “broad spectrum” though, SPF technology only blocks UVB light. UVB light is the type that causes most sunburns and skin cancers. UVA light causes wrinkles and other visible signs of aging.

Why did you use the word “theoretically” when talking about SPF?

I don’t want to give anyone a false sense of security. And, I also don’t want anyone who burns really easily doing the math and thinking they can stay on the beach for hours without any problem, just because they put on SPF 30 sunscreen once and never reapplied it.

The key phrase above was “if used properly.” Most people only apply about one-third of the sunscreen they actually need. They use one tablespoon per application, when you really need three. That’s the equivalent of a quarter cup!

Also, both swimming and sweating can make sunscreen wear off much faster, so it needs to be reapplied frequently. We recommend reapplying sunscreen at least once every two hours, but more often if you’re playing in the water or perspiring profusely.

How does clothing made specifically to protect skin from UV light differ from regular clothing? 

What makes these fabrics special is the material they’re made out of, how tightly they’re woven and, sometimes, how they’re processed. Many of these garments are woven very tightly to block the sun’s rays. Others are dyed with or soaked in special chemical solutions that basically give the fabric a natural sunscreen, such as zinc oxide. 

Applied coatings can fade over time, though. So, you may notice the colors changing or the fabrics getting stretchier as you wash these garments. Those could be signs that they’re losing their UPF protection and need to be replaced. 

Check the label of each item or visit the manufacturer’s website for details. Some garments are designed to retain their UPF for up to 100 or even 500 washes. Other manufacturers claim their garments’ UV protection never wears out. 

Doesn’t regular clothing protect us against UV light?

Your clothing’s UPF value depends on the type of fabric it’s made out of, the color of the fabric and whether or not the fabric is wet. Dry, tightly woven, dark-colored fabrics offer the most protection. 

But the stretchier a fabric is, the less protection it offers, especially when fully extended. Something like dry, dark biking shorts start out at about UPF 85 before the material is stretched, and UPF 8 when worn. And, if they get wet, too, they drop even more, to UPF 4. 

A conventional bathing suit made out of dark, stretchy material has a UPF 8.6 when dry, while a white or light-colored bathing suit only offers about UPF 4 when wet. Most swimsuits provide about a UPF 5, so roughly 20% of the sun’s rays will still reach your skin.

Does that mean we should all be putting on sunscreen before we put on our swimsuits?

No. The current recommendation is to apply sunscreen only to exposed skin. Just keep in mind that traditional bathing suits might not offer as much protection to covered areas as you think. 

Most of the Mohs surgeries I perform in the buttock fold area have one thing in common: they’re all on people who are shocked. Many, however, have a history of sunning themselves face-down in a bathing suit. I also do a lot of Mohs surgeries on UV-associated cancers around sensitive genital skin, due to tanning bed use.

Is there any way to gauge how protective my regular clothing is?

Yes. One way is to hold it up to the sun. If you can see the sun’s light through the fabric, then its UV rays are getting through. But the weave of a fabric matters. So, if you have something with a very tight weave and hold it up to a window, then you might not see the sun. 

If you’re really concerned, you can always look for UPF 50+ swim garments that block 98% of the sun’s rays. It’s much easier to find swimsuits with sun-protective materials now than it used to be. It’s also much easier to buy one of those than it is to try to put sunscreen everywhere.

According to the American Academy of Dermatology, any garment with a UPF between 30 and 49 is considered good protection, while a garment with a UPF 50 or higher is considered excellent protection. Anything under UPF 30 is not considered highly sun protective. 

Is there any way to add UPF to my clothing myself?

Yes. There’s a colorless fabric dye you can use as a laundry treatment. You add one package to a load of laundry and let it soak. The effect is said to last for up to 20 washes. It’s available at most fabric and craft stores.

Request an appointment at MD Anderson online or call 1-877-632-6789.