WTF is SPF: Decoding Sun Protection Numbers

You may know that SPF stands for sun protection factor, but what does SPF really mean? Today, we’re diving deep into the world of SPF: how much protection does an SPF 15 sunscreen offer compared to an SPF 50? Does the numerical value of an SPF rating make a difference to your protection levels? While things might seem straightforward, the reality is far more nuanced. 

Let’s brush up on some quick SPF facts. SPF 15 blocks 93% of UVB rays, SPF 30 blocks 97% and SPF 50 blocks 98%. On the face of things, the difference between a 15 and a 30, or 30 and a 50 might seem immaterial. However, this interpretation can be misleading for the following reasons. 

Firstly, these percentages only apply if you are meticulously applying the recommended amount of sunscreen, which is, on average, 1.25ml for the face- much more than what most people usually use. In fact, we found out from the Waikato Hospital dermatologists that 80% of people are applying significantly less which reduces the actual protection they can be getting. 

Secondly, when we only focus on the percentage of UVB rays blocked, it can paint an incomplete picture. Instead, it is vital that we are also considering the amount of UV radiation that penetrates the skin, not just what is blocked. For example, instead of understanding an SPF 15 as blocking 93% of UVB rays, it allows 7% of UVB rays to reach the skin. As such, an SPF 30 allows less than 3% of UVB rays to reach the skin while an SPF 50 allows less than 2%. This means that an SPF 15 lets in almost four times more UV radiation than an SPF 50. Thinking about sun protection factors in this way helps to better understand the heightened differences between different sunscreen products and the potential sun exposure.

Turns out using an SPF with a higher value does make a noticeable difference, but it is essential to balance that with other factors including usability and costs. For example, higher SPF products tend to contain more active ingredients which can feel greasier on the skin and cost more than other sunscreens. Why is this an issue? According to the Melitta Skin Sun Habits Survey 2022, 80% of 166 respondents stated that consistency is a major deterrent for daily SPF use while less than 50% were willing to spend more than $60 on a single sunscreen. As a result, higher SPF products may discourage users from applying the adequate amount which, as we learned, negates the benefits of reaching for higher SPF levels. 

The best advice is to select the highest SPF that feels great to the touch while fitting within your skincare budget. However, at the end of the day, regular application is crucial to maintaining the effects of sun protection from your SPF. Today, many people are still under the false impression that higher SPF sunscreens require less frequent application, but we have to remember that physical activity can wear off the protective film, reducing effectiveness over time. In fact, 90% of SPF products in New Zealand only offer 2 hours of baseline protection, but depending on what you are doing, you may need to reapply more frequently. 

Furthermore, beyond sunburn (UVB rays), it is equally as important to consider the impact of UVA rays which are primarily responsible for skin ageing and pigmentation as they tend to penetrate deeper into the skin. When shopping for your next SPF, look for a label that states “broad spectrum” or “UVA protection” as well as “UVB protection” for optimal sun defence. In some jurisdictions such as Australia and New Zealand, higher SPF sunscreens are required to provide broad-spectrum protection thanks to the updated regulations in 2022.  

Remember, sunscreen is just one piece of the puzzle that makes up a robust sun protection regime. Physical barriers such as clothing, hats and sunglasses can often provide even more reliable protection for sunburn as they do not require reapplication. While SPF plays a critical role in protecting you against UV radiation, minimising direct sun exposure and remembering to use physical barriers can keep you safer for longer. 

For those keen to deepen their understanding of sunscreen and its correct application, further exploration into topics such as the amount of sunscreen needed, integrating sunscreen into your daily routine and the key differences between chemical and physical sunscreen ingredients, keep up with Glow Academy for more!