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What does SPF Mean?

Tricia Christensen
Updated Mar 03, 2024
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Sun Protection Factor (SPF) represents the length of time you can stay out in the sun without burning, multiplied by the corresponding number. So a person who would normally start to burn in 10 minutes, could theoretically have 150 minutes of sun protection with a sunscreen that has an SPF of 15.

Regardless of SPF number, testing of sunscreen does not really correspond to the amount of time you can stay out in the sun without burning because sweating, clothing rubbing against the skin, and water sports will all wear the sunscreen off. Tests also use much more sunscreen than do most people, so SPF number results can be inaccurate. Usually, an SPF 15 rated sunscreen will give your about an hour of protection before you should reapply sunscreen. This, of course, varies from person to person. It also helps to wear protective clothing, hats and sunglasses.

The SPF number only relates to ultraviolet B (UVB) protection. Ultraviolet A (UVA) protection is not measured through these numbers, and until recently, frequently was not available in sunscreens. UVB rays are more potent, quicker to produce sunburn, and have been linked to skin cancer. UVA is associated with aging of the skin, and along with UVB exposure, may increase risk or facilitate skin cancer. UVA though milder, is still not safe.

Some chemicals found in new sunscreens that also boast an SPF number can help block UVA rays. Chemicals like Parsol 1789 block both UVA and UVB rays. Unfortunately, these chemicals are a cause of concern to environmentalists because they have been found in water, groundwater and soil. Potential long-term effects of exposure are unknown.

What remains important to remember is that sunscreen strength is less important than frequent application, and avoidance of sun between 10 am and 4 pm, when UVB rays are strongest. Sunscreen protection should always be combined with protective clothing and sun avoidance during the hottest and brightest parts of the day.

Some people do pay more for higher SPF protection, and this may make sense for those with lighter skin. Doctors generally recommend purchasing an sunscreen of 15 or higher. There are lower ones, which will cause the skin to tan or burn in under an hour. It may be unnecessary to purchase an SPF higher than 15, except possibly for infants, if you can be vigilant about reapplying the sunscreen every hour, and after swimming or very vigorous physical activity.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Tricia Christensen
By Tricia Christensen
With a Literature degree from Sonoma State University and years of experience as a The Health Board contributor, Tricia Christensen is based in Northern California and brings a wealth of knowledge and passion to her writing. Her wide-ranging interests include reading, writing, medicine, art, film, history, politics, ethics, and religion, all of which she incorporates into her informative articles. Tricia is currently working on her first novel.
Discussion Comments
By DylanB — On Dec 10, 2012

@orangey03 – The problem is probably that you are using lotion instead of spray. Try purchasing a clear, no-rub spray with SPF 30.

I used to have trouble with even the waterproof lotion rubbing off in spots. If I were to lie down on a float, the lotion would stick to the raised spots on the float and I would wind up with red rings on my body.

I started using the spray, and almost nothing can remove it. In fact, it is hard to get the stuff off in the shower when scrubbing with a cloth and soap!

At least I know that I'm well protected. It dries quickly, so I can go about my business. Reapplication is very easy, and you don't have to do it often.

By orangey03 — On Dec 10, 2012

Sunblock with SPF 15 does almost nothing for me. I have very fair skin, and I burn in about thirty minutes, even while wearing SPF 15.

I buy lotion with SPF 30, but even that only lasts about an hour. Is there anything I can do to make my sunscreen last longer? I'm tired of reapplying so often!

By cloudel — On Dec 09, 2012

I wear foundation with SPF 15 in it. I used to have trouble deciding between regular sunscreen and regular foundation with no SPF, so when I found this product, I was thrilled.

Now, I can walk around outside without feeling that all my flaws are exposed. I can go to the park on my lunch break without worrying about getting any sun damage while eating lunch on that park bench in the sun.

I was afraid when I first bought the makeup that it might smell like sunscreen, but it doesn't. In fact, it has almost no odor at all. After I apply it, I don't even smell it.

By kylee07drg — On Dec 08, 2012

@anon179152 – SPF 50 would be good for you. Some people say that when you go higher than SPF 30, you are probably just wasting money, but I have seen that SPF 50 works better.

One year, I went to the beach wearing SPF 30, and I burned, even though I reapplied every two hours. The next year, I wore SPF 50 instead, and I didn't even turn pink.

By anon249709 — On Feb 21, 2012

SPF is an initialism, not an acronym. You can't pronounce SPF.

By anon179152 — On May 23, 2011

My skin gets damaged in the sun as in i get a lot of spots and pigmentation. would getting a moisturizer of SPF 50 be too much? Should i just get spf 30 because at the moment I'm using spf 25 and that's not very good?

By anon176101 — On May 14, 2011

yeah I'm doing a science project on if spf 10 or spf 30, which one protects your skin better.

well, i guess we all know that it is spf 30, right?

By anon72028 — On Mar 21, 2010

yeah when i was little my dad never put on sunscreen. he always wore a cotton t-shirt outside.

Some dads. ha!

By averagejoe — On Jun 21, 2008

Did you know that a regular cotton t-shirt is the equivalent of SPF 5 sunscreen?

Tricia Christensen
Tricia Christensen
With a Literature degree from Sonoma State University and years of experience as a The Health Board contributor, Tricia...
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