SPF stands for Sun Protection Factor. It is a measure of how well a sunscreen protects your skin from ultraviolet B (UVB) rays, which are the main cause of sunburn and contribute to skin cancer
. The SPF number indicates how much longer you can theoretically stay in the sun without getting sunburned compared to no protection. For example, if your skin would normally burn after 10 minutes in the sun, applying an SPF 30 sunscreen means you could stay in the sun approximately 30 times longer (about 300 minutes) before burning
. However, this is a simplified estimate and actual protection time varies based on factors like skin type, sun intensity, and amount of sunscreen applied. Also, SPF primarily measures protection against UVB rays, not UVA rays, which can also damage skin. Sunscreens labeled "broad-spectrum" protect against both UVA and UVB rays
. In terms of UVB protection percentage:
- SPF 15 blocks about 93% of UVB rays
- SPF 30 blocks about 97%
- SPF 50 blocks about 98%
So higher SPF numbers provide incrementally better protection, but no sunscreen blocks 100% of UVB rays
. In summary, SPF is a relative measure of how well sunscreen protects your skin from sunburn-causing UVB rays and how much it extends your safe sun exposure time
