UV Index → SPF Ladder

Summary

SPF blocks a fixed percentage of UVB; the practical floor rises with the UV index, not the season.

Takeaway

SPF 30 blocks 97% of UVB; SPF 50 blocks 98%. Reapplication beats higher numbers.

Citations · 1

1. [01]
   WHO (2024). Global Solar UV Index: A Practical Guide. World Health Organization
   Source