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Buying sunscreen can be confusing. Here are some common terms and definitions that may help you find what you need:
UVA. Ultraviolet A is long-wave radiation generated by the sun that penetrates more deeply than UVB, causes wrinkling and leathering, damages connective tissue, and causes tanning but is less likely to cause an immediate burn. UVA exposure is key in the development of melanoma.
UVB. Ultraviolet B is short-wave radiation. It reddens and burns the skin and causes tanning. UVB also promotes basal and squamous cell carcinoma and may worsen the effects of UVA.
SPF. Sun protection factor. This measures the length of time a product protects against UVB, compared with no protection at all. If it takes you 20 minutes to start turning pink without any protection, an SPF 15 sunscreen would allow you to stay in the sun for 5 hours (20 minutes times 15) before burning, provided you reapply the sunscreen whenever it wears off. Reality isn't quite so precise, though--skin color, season, locale, sweat, and water are all variables.
Once you go beyond SPF 15, increases mean less, since SPF 15 blocks 93 percent of UVB. Even though SPF 15 is twice as effective as SPF 8, SPF 30 blocks only 4 percent more UVB than SPF 15. Got it?
More on skin cancer
Dr. Bortz's Words of Wisdom: judge this book by its cover.
The Dark Side of the Sun: back to the main story.
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