SPF vs UPF: What's the difference?

What do SPF and UPF actually measure?

UPF is measured in a laboratory using an instrument that measures UV passing through fabric. A UPF 20 fabric lets through one twentieth of the UV that would reach bare skin. Fabric composition, weave, stretch and wear affect the rating, so the number describes the material rather than every situation in which you wear it.5

Is SPF 50 the same as UPF 50?

No. The numbers come from different tests and cannot be treated as interchangeable. UPF 50 fabric blocks 98 percent of UV radiation, allowing 2 percent through. SPF 30 sunscreen blocks about 97 percent of UVB rays; higher SPFs block slightly more, but none blocks all UVB. SPF alone does not tell you the sunscreen's UVA protection.123

SPF is not a multiplier for safe time outdoors. SPF 50 does not mean you can stay outside 50 times longer or wait longer between applications. Sun intensity changes with the time of day and location, and higher SPF sunscreens need the same regular reapplication as lower SPF sunscreens.13

Which protection should you choose?

For everyday outdoor use, choose broad spectrum, water resistant SPF 30 or higher and clothing with UPF 30 or higher. UPF 30 to 49 offers very good protection; UPF 50+ offers excellent protection. For extended outdoor exercise, choose UPF 50 clothing and broad spectrum, water resistant SPF 50+ on uncovered skin.346

Coverage matters as much as the fabric rating: long sleeves, long pants or skirts, and a hat protect more skin. A UPF label describes the fabric, not the missing sleeves, which remain impressively bad at blocking sunlight. Choose a tightly woven hat with a brim of at least three inches to shade the face, ears and neck.2

Ordinary clothing can also protect against UV. Tightly woven fabrics and darker colors generally protect better than thin, loosely woven fabrics and lighter colors. Choose a loose fit because stretching can open gaps between fibers. Wet fabric often provides less protection, especially cotton; change into dry clothing after swimming. Worn, threadbare fabric also provides less protection.4

How to use SPF and UPF together

1. 1Put on clothing that covers as much skin as practical, plus a protective hat and sunglasses.
2. 2Apply sunscreen generously to dry, uncovered skin 15 minutes before going outdoors. Most adults need about one ounce to cover exposed skin, depending on body size and coverage.
3. 3Cover commonly missed areas, including ears, neck, hands and tops of feet. Use SPF 30 or higher lip protection.
4. 4Reapply sunscreen about every two hours outdoors and after swimming or sweating, following the label. Water resistance lasts for the labeled 40 or 80 minutes, not indefinitely.
5. 5Seek shade and limit sun exposure, especially between 10 a.m. and 2 p.m. Clothing and sunscreen are parts of protection, not substitutes for shade.

Who needs extra care?

People of every skin color need sun protection, including on cloudy days. For sensitive skin, mineral sunscreens containing zinc oxide or titanium dioxide are an option. Some medications increase sun sensitivity; ask your health care professional about precautions if you take medication. Keep babies younger than six months out of direct sun, use protective clothing, and ask a doctor before applying sunscreen.137