SPF stands for Sun Protection Factor , and It measures the level of protection a sunscreen offers against UVB rays, the primary cause of sunburn and skin cancer. The SPF factor indicates how long it takes for UVB rays to redden the skin when using the sunscreen compared to not using any sunscreen at all.
While UVB rays primarily cause sunburn, UVA rays penetrate deeper into the skin, leading to premature aging and skin damage. Therefore, it's essential to choose a sunscreen that offers broad-spectrum protection, shielding your skin from both UVA and UVB rays.
The SPF value of a sunscreen is determined by its ability to absorb and reflect UV radiation. SPF is calculated by comparing the amount of time it takes for skin to burn with and without sunscreen. For example, if it takes 10 minutes for your unprotected skin to start turning red, a sunscreen with SPF 30 will theoretically provide 30 times longer protection, or 300 minutes.
SPF ratings typically range from 15 to 50+, with higher numbers indicating greater protection. Dermatologists generally recommend using a broad-spectrum sunscreen with an SPF of 30 or higher for adequate protection against both UVA and UVB rays.
The duration of protection provided by a sunscreen depends on various factors, including the intensity of the sun's rays, your skin type, and how much sunscreen you apply. As a general rule, SPF 30 provides protection for approximately 2 hours, but reapplication is necessary every 2 hours, especially if you're swimming or sweating.
Ultimately, the SPF you choose depends on your skin type, sun exposure, and personal preferences. However, dermatologists recommend using a broad-spectrum sunscreen with an SPF of 30 or higher for daily use, regardless of weather conditions.
American Academy of Dermatology (AAD). 'Sunscreen FAQs.' [AAD](https://www.aad.org/public/ everyday-care/sun-protection/sunscreen-patients/sunscreen-faqs)
Skin Cancer Foundation. 'Understanding UVA and UVB.' [Skin Cancer Foundation](https:// www.skincancer.org/risk-factors/uv-radiation/uva-and-uvb/)
American Academy of Dermatology (AAD). 'Sunscreen: How to Help Protect Your Skin from the Sun.' AAD