Skin cancer is the most common cancer in the United States, but it's also the easiest to prevent with the proper protection.
Titanium dioxide and zinc oxide are minerals that physically block ultraviolet (UV) rays from reaching your skin, as opposed to other sunscreens that use chemicals to absorb UV rays. Minerals are considered the best protection against sunburn because they block both UVB rays (which cause sunburns) and UVA rays (which cause skin aging and cancer). Chemical sunscreens, on the other hand, don't always protect against UVA.
SPF is an FDA-regulated rating system that represents how long it will take for exposed skin to burn with the sunscreen applied. For example, if your unprotected skin usually burns in 10 minutes, a sunscreen with an SPF 15 would prevent a sunburn for 15 times that length of time, or 150 minutes. However, SPF only rates UVB rays, not skin damaging UVA rays. For that reason, never rely entirely on a sunscreen's SPF, and look for products that advertise "broad-spectrum protection," which means it protects against both types of rays.
The primary drawback to sunscreens with titanium dioxide or zinc oxide is that they can leave a white tint on your skin. To make the lotions transparent, manufacturers shrink titanium dioxide or zinc oxide particles down to nano-sized particles. Because smaller particles can act differently than larger particles when they enter the body, these nano-sized particles have been cause for concern: Research indicates that nanoparticles of titanium dioxide are small enough to bypass your body's "blood-brain barrier" (a natural defense against foreign substances in the bloodstream) and enter the brain where they can damage brain cells. Larger particles, however, are blocked by that barrier and don't pose this problem. Fortunately, a 2006 Australian government literature review on the topic found that neither titanium dioxide nor zinc oxide penetrate the skin deep enough to actually enter the bloodstream, and most scientific evidence supports the fact that nano-sized particles of these ingredients are often trapped in the outer layer of the skin and not absorbed (they should always be avoided when used in powders that may be inhaled). However, if you'd rather err on the side of safety, opt for sunscreens that use micronized ingredients (particles larger than 100 nm), which are mostly transparent but may still offer a slight tint.
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Tuesday, June 10, 2008
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