How sunscreen SPF calculated and why it matters
Sunscreen is your best defence against painful burns and serious future health risks.
If you are still fighting against the use of sunscreen, then let us bring you up to speed.
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The importance of sunscreen has been amplified over the decades, and finally, more people are beginning to understand that a straightforward step can help them avoid heartbreak.
While it might seem like an exclusively braai, pool, or beach necessity, sunscreen should be part of your daily routine.
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The Skin Cancer Foundation emphasises that when used as directed, sunscreen can:
- Reduce your risk of skin cancer and precancerous skin conditions. Studies show that regular daily use of SPF 15 sunscreen can reduce your risk of developing squamous cell carcinoma (SCC) by about 40% and lower your melanoma risk by 50%.
- Help prevent premature skin ageing caused by the sun, including wrinkles, sagging and age spots.
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Dermatologist Dr David Leffell, CEO of Yale Medical Group and a member of Yale Cancer Centre, is one of the many medical professionals who have made it their mission to highlight the importance of how "Practicing good sun protection, including the use of sunscreen, could save your life."
But how can you truly protect yourself if you don't understand how it works?
Here are a few basic things you need to know about SPF.
- SPF stands for Sun Protection Factor.
- It indicates a sunscreen's ability to block UVB rays.
- SPF was pioneered at the Coppertone Solar Research Center in 1972.
- In 1978, the FDA published an SPF method based on Coppertone’s system.
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How is SPF calculated?
The numbers (15, 30 or 50) represent the approximate measure of time a person who has applied sunscreen can stay out in the sun without getting burned.
Example: If it takes 20 minutes to burn without sunscreen and 600 minutes to burn with sunscreen applied, divide the time with sunscreen applied by the time without sunscreen applied, resulting in an SPF of 30.
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Theoretically, you should have approximately 10 hours in the sun, but it’s not an exact science because the amount of UV light that reaches us depends on a number of factors, including cloud cover, the time of day, and the reflection of UV rays off the ground.
It’s generally recommended that you reapply sunscreen every two hours or more frequently.
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How to correctly apply sunscreen
- Use a water-resistant, broad-spectrum sunscreen, which protects against both UVB and UVA radiation, with an SPF of at least 30.
- Apply your sunscreen in an even coat 20 minutes before heading to the beach or pool. Sunscreen sprays will easily provide you with the even coat you need.
- When applying, Dr Leffell recommends starting with your scalp and face, even if you plan on wearing a hat. Make sure you’ve covered the ears, nose, and under the eyes before moving down to the shoulders.
- Other important areas that you may forget to cover, but shouldn’t, are the tops of your feet, the backs of your hands, and your chest.
- Water-resistant doesn’t mean waterproof.
You know you’re applying your sunscreen properly if, after the first time you’ve used it, you haven’t gotten a burn.
I always tell patients to reapply every couple of hours while you’re active outdoors. And always reapply when you come out of the water or if you’ve been sweating a lot, regardless of whether the label says water resistant.
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It's important to note that sunscreen only extends your time in the sun, and even if you are not sunburned, you are still doing damage to your skin.
Dr Patricia Agin, president of Agin Suncare Consulting, says, "At the end of the 600 minutes, you will have accrued enough UV to cause a sunburn (one Minimal Erythema Dose or MED) but there is pre-MED damage done to skin cells’ DNA and to the skin’s supporting structure of collagen and elastin that is not visible and happens even before you sunburn. These types of damage can occur without sunburning. So you can’t measure all the damage done to your skin by only being concerned about sunburn."
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