Why SPF 50 isn’t Necessarily Better than SPF 25
SPF (Sun Protection Factor) measures the protection a sunscreen offers against UVB rays, which are responsible for sunburn and contribute to skin cancer. The difference in “real-life” protection between SPF 50 and SPF 25 is often less dramatic than it appears based solely on the SPF number.
Theoretically Speaking
- SPF 25 blocks about 96% of UVB rays
- SPF 50 blocks around 98% of UVB rays
This means that the difference in UVB protection between SPF 25 and SPF 50 is about 2%. While SPF 50 offers slightly more protection, the real-world benefit is marginal in everyday conditions.
In the Real World
- In real-life use, the effectiveness of any sunscreen depends more on how generously it is applied and whether it’s reapplied regularly. Studies show that most people don’t apply enough sunscreen (typically only 25-50% of the recommended amount), which reduces its protection regardless of SPF.
- Higher SPF does provide longer protection under intense sun exposure, but the difference in protection time isn’t as large as the SPF numbers suggest. SPF 25 can protect your skin for about 250 minutes (4 hours) before it starts to burn, while SPF 50 would extend this time to around 500 minutes (8 hours) under controlled conditions. Consider how much sun exposure you will get in a day, is it just in minutes/hours? How much SPF do you really need?
- While SPF measures UVB protection, broad-spectrum sunscreens also protect against UVA rays. Mineral sunscreens, especially those with zinc oxide, can offer better UVA protection (against sun-aging) and pigment reduction, regardless of their SPF rating.
