SPF Is Not a Sun-Time Multiplier
SkinArticleDo not turn a sunscreen number into a personal allowance of hours outdoors.
In this article
An SPF number does not tell you how many hours you can stay in the sun. FDA1 explains that SPF relates to the amount of solar exposure, not directly to exposure time. Multiplying your usual time to burn by SPF is not a reliable allowance.1
Why the calculation fails
Solar intensity changes with time of day and geographic location. The same amount of time outdoors can mean different amounts of exposure. SPF measures sunburn protection and primarily indicates protection against UVB radiation.1
Plan protection instead
Look for broad-spectrum protection, which covers UVA and UVB. Follow your sunscreen’s directions and use other protective measures, including covering clothing and shade.1
If you are organizing an outdoor day, keep the product instructions with your planning notes. Ask a pharmacist or dermatologist to clarify anything you cannot understand.
Try: “I was using SPF to estimate how long I could stay outside. Can you help me understand the label and plan sun protection?”
Skin, Head to Toe includes a label decoder and visit script. Use them to organize product questions for professional advice. See the book.
This article is for general educational purposes only and is not medical advice. It isn't a substitute for diagnosis or treatment from a qualified healthcare professional who knows your health history. Please don't ignore professional advice or delay getting care because of something you read here. If you think you may be having a medical emergency, call 911 or your local emergency number right away. Girl Playbook does not endorse any specific product, test, or provider.
Girl Playbook sells this book. It provides education and worksheets, not individualized medical care.
Sources
The research behind this article, in the order it’s cited. How we source our articles.
- U.S. Food and Drug AdministrationSunscreen: How to Help Protect Your Skin from the Sun (opens in a new tab)abcd
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