What Does SPF Mean?

I get asked this one a lot, usually by a patient deciding between one of our many sunscreens. Is a higher SPF worth more? The answer is yes, technically. But probably not in the way you are imagining.

SPF stands for Sun Protection Factor, and it measures how much UV radiation it takes to cause sunburn on protected skin compared to unprotected skin. The math looks straightforward on paper:

• SPF 30 blocks about 97% of UVB rays. 
• SPF 50 blocks about 98% of UVB rays.
• SPF 100 blocks about 99% of UVB rays.

But, here is where the SPF number starts to matter less than you think.

Most people apply about 25 to 50% of the recommended amount of sunscreen. The SPF you see on the label assumes a full, even, generous application (about a nickel-sized amount for just your face, and a shot glass worth for your body.) When you under-apply SPF 100, its real-world protection can drop to the equivalent of SPF 50 or less. The number on the bottle assumes behavior that most of us are not doing.

SPF only measures protection against UVB rays, which are the ones that cause burning. UVA rays go deeper into the skin and are responsible for premature aging, pigmentation, and a significant portion of skin cancer risk. That is why broad spectrum coverage matters so much. A sunscreen can have a high SPF number and still leave you unprotected against UVA if it is not formulated for broad spectrum protection.

If I had to rank the things that make the biggest difference in real sun protection, the SPF number would not be at the top of the list. Instead, think of your SPF in these terms:

• Reapplication. This is the one that most people skip. Sunscreen breaks down with UV exposure, sweat, and water. Reapplying every two hours is non-negotiable, and after swimming or sweating heavily, sooner than that.
• Broad spectrum coverage. Look for this on the label. It means the formula protects against both UVA and UVB.
• How much you apply. A thin swipe is not enough. Most people use far less than they should, which means their actual protection is a fraction of what the label says.
• Daily consistency. Sun damage is cumulative. The damage does not reset overnight. Every day you skip sunscreen, even during cloudy weather, adds up over time.

If you are reading this from the Big Island, your UV exposure is not the same as someone applying sunscreen on a winter morning in Seattle.

The UV index in Kona regularly hits 11 or above, which is classified as extreme. Our proximity to the equator means the sun’s rays hit at a more direct angle year-round. If you live or spend time in higher elevation areas like Waimea or Volcano, UV exposure increases further because there is less atmosphere filtering the radiation. And because our weather is beautiful most of the year, we are outdoors consistently in a way that mainland residents are not.

For the many reasons listed above, I have a lot of different sunscreen in my bathroom cabinet, car, purse, stroller, etc., and for all the different environments:

• Daily driving and commuting You are getting more UV exposure through car windows than most people realize. UVA rays penetrate glass. A lightweight daily moisturizer with SPF 30 to 50 broad spectrum is enough to cover this activity, as long as you are not spending extended time outdoors. 
  • Dr. Scheel Radiant Hydration is my favorite and the one I consider the most luxurious. 
• Working at a desk near a window: Alastin HydraTint is a great alternative to foundation. 
• Beach day or pool day: This is where you need water-resistant SPF 50 minimum, applied generously 15 minutes before you go outside, and reapplied every 80 minutes or immediately after toweling off. Do not forget ears, the back of the neck, and the tops of feet.
• Surfing or water sports: Mineral sunscreen is worth considering here because it sits on top of the skin rather than absorbing into it, and it tends to hold up better with repeated water exposure. SPF 50 mineral, reapplied frequently.
  • TiZo is for the paddlers! This won’t sweat into your eyes and burn, but it is more difficult to remove at night. 
• Outdoor dining or a casual afternoon outside People consistently underestimate how much UV exposure adds up during a two hour lunch on a lanai. SPF 50, reapplied if you are outside past the two hour mark.
  • Dr. Scheel Antioxidant TINTED Physical Sunscreen has such a nice creamy texture. 
  • Dr. Scheel’s Glow Drops are for the patients who don’t like thick sunscreen. 
  • Isdin Actinica is so light and spreadable, and it is my second favorite non-tinted sunscreen. 
  • Isdin Ageless is the tinted SPF. This works better for patients who have a deeper skin tone.
  • This is a brush that I think of like a setting powder. It is not a replacement for sunscreen. It will not provide enough coverage, but I put it on my hairline.

Choose a broad spectrum formula you actually enjoy wearing, apply enough of it, and reapply throughout the day. That is where the real protection lives.

Have questions about which sunscreen is right for your skin type or lifestyle? Email me anytime at mmahoney@drmonicascheel.com or call my direct line at (808) 666-2078.

Mahalo for reading — here is to happy, healthy, glowing skin.