Blog Details

Sun Protection Factor (SPF)

Sun Protection Factor (SPF): Definition and Explanation

What is SPF?

SPF stands for Sun Protection Factor and is a numerical rating that measures how well a sunscreen protects the skin from ultraviolet B (UVB) rays, which are primarily responsible for causing sunburn and contribute significantly to skin cancer.

What Does the SPF Number Mean?

• The SPF number indicates the theoretical multiple of time you can be exposed to UVB rays without getting sunburned compared to unprotected skin. For example, if your skin normally burns after 10 minutes, an SPF 30 sunscreen suggests you could remain in the sun 30 times longer (about 300 minutes) before burning.
• However, this is an approximation influenced by many factors, including skin type, UV intensity, geographic location, time of day, and proper sunscreen application.
• SPF also corresponds to the percentage of UVB rays filtered out:
  • SPF 15 filters about 93% of UVB rays
  • SPF 30 filters about 97%
  • SPF 50 filters about 98%
  • No sunscreen can block 100% of UVB rays.

Protection Spectrum

• SPF specifically measures protection against UVB rays.
• For protection from both ultraviolet A (UVA) and ultraviolet B (UVB) rays, broad-spectrum sunscreens are recommended, as UVA contributes to skin aging, pigmentation, and some cancers.

Important Considerations

• Proper application of sunscreen (about 2 milligrams per square centimeter of skin) is critical to achieve the labeled SPF effectiveness.
• Sunscreens must be reapplied every two hours or immediately after swimming, sweating, or towel drying.
• Higher SPF offers incremental benefits but should not replace other sun-safe behaviors such as seeking shade and wearing protective clothing.

Key Points

• SPF measures sunscreen efficacy against UVB-induced sunburn.
• Higher SPF numbers mean greater UVB protection but do not indicate longer protection time exactly.
• Broad-spectrum sunscreens protect against UVA and UVB rays.
• Correct application and frequent reapplication are essential for effective sun protection.

Consult with Our Team of Experts Now!

For personalized sun protection advice and suitable sunscreen recommendations fitting your skin type and lifestyle, consult with our dermatologists to ensure effective daily sun safety.

References:

1. Herzog SM, Lim HW, Williams MS, de Maddalena ID, Osterwalder U, Surber C. Sun Protection Factor Communication of Sunscreen Effectiveness: A Web-Based Study of Perception of Effectiveness by Dermatologists. JAMA Dermatol. 2017 Mar 1;153(3):348-350. doi:10.1001/jamadermatol.2016.4924. Available at: https://doi.org/10.1001/jamadermatol.2016.4924​
2. Food and Drug Administration. Sun Protection Factor (SPF). 2017 Jul 13. Available at: https://www.fda.gov/about-fda/center-drug-evaluation-and-research-cder/sun-protection-factor-spf​
3. Diffey BL. Sunscreens and Sun Protection Factor: Rules and Reality. Photodermatol Photoimmunol Photomed. 2001 Feb;17(1):49-54. doi:10.1034/j.1600-0781.2001.170108.x. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1128750/​
4. Narla S, Lim HW. Sunscreens and Photoaging: A Review of Current Literature. Dermatol Clin. 2021 Aug;39(3):383-390. doi:10.1016/j.det.2021.05.002. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8361399/​
5. Armstrong BK, Kricker A. The Epidemiology of UV Induced Skin Cancer. J Photochem Photobiol B. 2001 Jul;63(1-3):8-18. doi:10.1016/s1011-1344(01)00198-x. Available at: https://doi.org/10.1016/s1011-1344(01)00198-x