SPF in sunscreen 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 type of UV radiation that causes sunburn and can contribute to skin cancer
. The SPF number indicates how much longer you can theoretically stay in the sun without burning compared to no protection. For example, if your skin normally burns after 10 minutes in the sun, applying an SPF 30 sunscreen means you could stay in the sun about 30 times longer (around 300 minutes) before burning, under the same conditions
. However, this is an approximation because actual protection depends on factors like skin type, sunscreen amount applied, intensity of sunlight, and reapplication frequency
. SPF only measures protection against UVB rays, not UVA rays. UVA rays also damage skin and contribute to premature aging and skin cancer. For protection against both UVA and UVB rays, you should look for sunscreens labeled "broad- spectrum"
. In terms of UVB protection efficiency:
- SPF 15 blocks about 93% of UVB rays
- SPF 30 blocks about 97%
- SPF 50 blocks about 98%
The increase in protection is not linear; higher SPFs provide only slightly more UVB protection, but dermatologists generally recommend using SPF 30 or higher for effective protection
. In summary, SPF is a relative measure of how well a sunscreen protects your skin from UVB radiation and sunburn, helping you compare different sunscreens' effectiveness but not directly indicating exact safe sun exposure time
. Key points:
- SPF = Sun Protection Factor, measures UVB protection
- Higher SPF means more UVB blocked, but not 100%
- SPF number roughly multiplies the time before sunburn
- Does not measure UVA protection; use broad-spectrum for UVA + UVB
- Dermatologists recommend SPF 30 or higher for good protection
This explains what SPF is and how it relates to sunscreen effectiveness.
