What does SPF stand for? On a bottle of sunscreen, a lip balm or a daily moisturizer, SPF means Sun Protection Factor. The number after it tells you how well the product protects skin from the kind of sun rays that cause sunburn.
The number is a lab measurement, not a timer. Testers compare how much sun it takes to redden skin with the product on and without it. A higher factor means more protection against burning, but no number blocks every ray, and the protection fades as the product rubs, sweats or washes off.
Quick facts
Stands for
Sun Protection FactorType
Initialism, said S P FMeasures
Protection mainly from UVB rays, the burning raysSeen on
Sunscreen, lip balm, moisturizer, makeupCommon numbers
15, 30, 50Look for too
"Broad spectrum" on the labelOther meanings
Sender Policy Framework (email), spruce pine fir (lumber)
What does SPF stand for, word by word?
- S, Sun: the source of the ultraviolet light.
- P, Protection: what the product offers the skin.
- F, Factor: a number that compares protected skin with bare skin.
Sunlight carries two main kinds of ultraviolet rays that matter for skin. UVB rays cause most sunburns. UVA rays reach deeper and add to skin aging. The SPF number is mostly a measure of UVB protection. A product labeled broad spectrum has also passed a test for UVA, so that phrase is worth checking next to the number.
What the numbers mean on the bottle
| Label | UVB filtered, roughly |
|---|---|
| SPF 15 | About 93 percent |
| SPF 30 | About 97 percent |
| SPF 50 | About 98 percent |
The jump from 15 to 30 is bigger than the jump from 30 to 50. Doubling the number does not double the protection. Many skin doctors suggest SPF 30 or higher for time outdoors, but how you apply it matters as much as the number. Most people use far less than the amount used in testing, which lowers the real protection.
How SPF is used in real life
Line on a sunscreen tube: "Broad spectrum SPF 30. Water resistant (40 minutes)." This means it was tested against both UVA and UVB, filters roughly 97 percent of burning rays when used as directed, and keeps working for about 40 minutes of swimming or sweating before you need more.
- Reapply at least every two hours outdoors, and right after swimming or toweling off.
- Water resistant labels list 40 or 80 minutes. No sunscreen is waterproof.
- Makeup and moisturizer with SPF help on a normal day, but a thin layer gives less protection than the label number.
- Cloudy days still let a good share of ultraviolet light through.
Other things SPF can mean
| Field | Stands for | Example |
|---|---|---|
| Email and IT | Sender Policy Framework | A record that lists which servers may send mail for a domain |
| Lumber | Spruce pine fir | A grade stamp on a two by four at a lumber yard |
| Computer networks | Shortest Path First | A way routers pick the quickest route |
If the letters show up in a work ticket about spam filters, it is the email meaning. At a building supply store, it is the wood. Everywhere else, it is almost always sunscreen. For more letters on bottles and labels, browse our famous acronyms list.
Saying and writing SPF
Say each letter: "S P F." Each letter gets its own beat, so it is an initialism. The number usually comes after the letters, as in SPF 50, and some labels write SPF50 with no space. Both are understood. Pick an over a here, since S is sounded "ess": "an SPF 30 lotion."
- "Pack the SPF 50 for the beach day."
- "My moisturizer has SPF, but I still use sunscreen for hikes."
- "Reapply your SPF after you get out of the pool."
- "Our email bounced because the SPF record was missing."
Common mix ups
- SPF vs UPF: UPF, ultraviolet protection factor, rates fabric such as sun shirts and hats. SPF rates products you put on your skin.
- SPF vs PA: some imported sunscreens show PA with plus signs, a rating for UVA. American labels use the broad spectrum phrase instead.
- SPF and time: the old trick of multiplying minutes by the number is not a safe rule, because sweat, water and thin layers cut protection.
For other health terms explained in plain words, see CPR and AED.
Questions people ask
Is SPF 100 twice as good as SPF 50?
No. SPF 50 already filters about 98 percent of burning rays, so a higher number adds only a small amount. Putting on enough and reapplying matters more.
What does SPF stand for in makeup?
It means the same thing as on sunscreen: Sun Protection Factor. Makeup with SPF offers some protection, but people often apply it too thinly to reach the number on the label.
Does a higher SPF mean I can stay out longer?
Not safely. The number does not set a time limit, and protection fades with sweat, water and rubbing. Reapply at least every two hours outdoors.
What is broad spectrum SPF?
Broad spectrum means the product protects against both UVA and UVB rays. The SPF number alone mainly describes UVB protection.
How do you pronounce SPF?
Say the three letters separately, S P F. Nobody says it as one word.