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Q: Does a sunscreen with a high SPF (sun protection factor) protect skin better than one with a lower SPF? How high should I go?
A: I wish I had a short, simple answer to this question, but it is a little complicated. As a dermatologist and photobiologist, I have studied the damaging effects of the sun’s ultraviolet (UV) radiation on skin, as well as how to protect against them. So I can walk you through a few important points that will make you more of a sun protection expert, too!
UV light, which represents a tiny percentage of the entire solar spectrum, is invisible to humans, because it has shorter wavelengths than the visible light range of the spectrum, which we can see. Within the UV spectrum, two types of radiation can damage the DNA in your skin cells and lead to skin cancer: UVB and UVA.
- UVB rays are the main cause of sunburn. UVB light also causes a delayed tanning response and contributes to skin aging. These shorter wavelengths affect the outermost layer of the skin and play a key role in developing skin cancer.
- UVA rays cause skin damage that leads to tanning as well as skin aging and wrinkles. The slightly longer rays travel deeper into the skin layers to cause damage. The shorter wavelengths of UVA rays also contribute to sunburn.
When UV light reaches your unprotected skin, damage to the DNA in your skin cells starts within minutes. Your immune system will repair some of this damage, but not all of it. Over time, the remaining DNA damage can cause mutations that lead to skin cancer. The UVA and UVB rays make a dangerous team. It’s important to look for the words “broad spectrum” on a product’s label, which means it has ingredients that can protect you from UVA as well as UVB rays. It’s crucial to protect your skin from both.
What Does SPF Mean?
The sun protection factor number measures how much of the sun’s ultraviolet (UV) radiation it takes to redden your skin when using a particular sunscreen (applied generously and evenly, and reapplied after two hours or after sweating or swimming) compared with the amount of UV radiation that reddens the skin without any sunscreen. As the SPF number increases, the protection from sunburn increases. A sunscreen’s SPF number reflects both the amount of UVB and UVA protection it provides.
Doesn’t SPF 30 mean I can stay outside 30 times longer?
That, unfortunately, is a common misperception. Think of SPF as a sunscreen filter strength, not a time allowance. SPF measures how much more UVB energy is needed to burn protected skin compared to unprotected skin. I repeat: It is not a time multiplier.
An SPF 30 sunscreen blocks about 97 percent of UV rays, but it does not mean you can safely stay outside 30 times longer than you could without it. UV intensity fluctuates throughout the day, and most people apply far less sunscreen than the amount used in lab testing, which dramatically reduces real-world protection. Sunscreen also breaks down with sweat, water and friction, which is why reapplication every two hours is essential regardless of the SPF number.
So what SPF number should I choose?
Under ideal conditions (like in a laboratory), a sunscreen with higher SPF protection and broad-spectrum coverage offers more protection against sunburn, UVA damage and DNA damage than comparable products with lower SPF values.
But, real life is not like a lab. People almost never use as much sunscreen product as recommended, and they often miss spots. In addition, products with very high SPFs often create a false sense of security. People who use them tend to stay out in the sun much longer. They may skip reapplying. And they may think they don’t need to seek shade, wear a hat or cover up with clothing. They end up getting a lot more UV damage, which, of course, defeats the purpose.
The Skin Cancer Foundation recommends a water-resistant, broad-spectrum sunscreen with an SPF of 50 or higher for any extended outdoor activities; and SPF 30 or higher for daily and incidental protection.
Regardless of the SPF, though, it’s important to apply at least one ounce (two tablespoons) 30 minutes before going outside and reapply it every two hours or immediately after swimming or sweating. No one’s exposed skin is the same size, but sunscreen should be applied thickly (like painting a fence), before rubbing it in.
People who have a history or high risk of skin cancer, genetic diseases such as albinism or xeroderma pigmentosum or certain immune disorders may need to cover up more and stay out of the sun at peak hours. Same goes for certain scenarios, such as hiking or skiing at high altitude or vacationing near the equator.
Sunscreen and More: The Bottom Line
Sometimes when you ask a question, you realize it’s the wrong question. The better question may be, “What is the best overall strategy to protect my skin?”
Here’s the answer: It’s important to know your family history and your own risks, and not to rely on high-SPF sunscreens alone. No single method of sun defense can protect you perfectly. Sunscreen, applied correctly, is just one vital part of a strategy that should also include seeking shade and covering up with sun-protective clothing (The Skin Cancer Foundation recommends UPF 50+), including wide-brimmed hats and UV-blocking sunglasses.
About the expert:
Steven Q. Wang, MD, a board-certified dermatologist and fellowship-trained Mohs surgeon, is director of dermatologic oncology and chief of dermatology at Hoag Memorial Hospital Presbyterian in Irvine, California. One of the country’s leading authorities on skin cancer detection, treatment and prevention, Dr. Wang is chair of The Skin Cancer Foundation Photobiology Committee.
