Fact or Fiction?: A "Base Tan" Can Protect against Sunburn

An SPF of 2 means it takes twice as long to burn. So if it takes you a half hour w/o a tan, a tan of SPF 2 should mean it takes an hour. Which is not inconsiderable.

http://www.scientificamerican.com/article/fact-or-fiction-a-base-tan-can-protect-against-sunburn/?WT.mc_id=SA_HLTH_20150526

By Dina Fine Maron | May 22, 2015

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Scientists came to this conclusion after studying the tanned buttocks of dozens of volunteers. In study after study they have found that a base tan affords almost no protection against future ultraviolet exposure. In fact, it actually puts otherwise pale people at risk of developing skin cancers. A base tan only provides an SPF, or sun protection factor, of 3 or less, according to the U.S. surgeon general. For beachgoers, that means if a person would normally turn pink after 10 minutes in the sun, an SPF 2 base tan would theoretically buy her another 10 minutes—or 20 minutes in total—before she burns. That, says David Leffell, the chief of dermatologic surgery and cutaneous oncology at Yale University School of Medicine, is “completely meaningless” in terms of providing protection.

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Getting a base tan from a tanning bed appears to be an even worse idea than preemptively exposing yourself to the sun. One study published this year looked at tanning from UVA light (the main staple of tanning beds) and found that the protection from future burn would not even meet an SPF 1.5 threshold. What’s worse, the body does not protect itself very effectively against the UVA rays that predominate in most tanning beds so indoor tanning can cause serious damage to your skin. Recent estimates suggest indoor tanning causes about 419,000 cases of skin cancer in the U.S. every year, which is almost double the number of cases of lung cancer linked to smoking. Still, UVA is often chosen for tanning beds because its longer wavelength penetrates deeper into the skin and is less likely to cause sunburn. The body will readily redistribute its existing melanin in response to UVA exposure—which results in immediate skin darkening—but UVB rays are better at triggering several more long-term protective mechanisms in response to cellular damage. Those include the production of more melanin, skin thickening and signaling DNA repair systems that try to correct for mutations before they are carried forward, says Heather Rogers, professor of dermatology at the University of Washington School of Medicine.

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