Sun Protection Factor (SPF) indicates how long it will take for ultraviolet B (UVB) rays to redden your skin when you use a sun protection product, compared to how long the skin would take to redden without the product. So, the SPF number gives you some idea of how long you can stay in the sun without burning. For example, if you normally burn in 10 minutes without sunscreen and you've applied a liberal dose of a sunscreen with an SPF number of 15, you should be protected from sunburn for 150 minutes. This does not mean that you are protected from other radiation damage. A broad spectrum sunscreen is required to give protection in the UVA range as well. An SPF rating does not measure Ultraviolet A (UVA) protection.
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