The number that follows SPF (Sun Protection Factor) indicates how well sunscreen protects skin from sunburn by filtering out ultraviolet B (UVB) rays.
A higher SPF number means that it will take longer for your skin to start to redden after applying sunscreen, compared to if you weren't wearing any. For example, if you can normally spend 10 minutes in the sun without burning, SPF 10 sunscreen would increase that time to 100 minutes. However, this is just an estimate and may vary depending on the weather, season, or your location.
According to science, SPF 15 sunscreen can filter out 93% of the sun's UVB rays, while SPF 30 can filter out 97%. However, the American Academy of Dermatology, The Skin Cancer Foundation, The FDA, World Health Organization, and the CDC all recommend using SPF 15 or higher, and reapplying every two hours.
