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Sun Series Part III: Sunblock Myths

Myth 1: More SPF is Always Better

Sun protection factor, or SPF, is a measure of how much UVB penetrates a sunscreen. The inverse of the SPF number is roughly how much UVB the sunscreen lets through. In other words, SPF 15 sunscreen lets through about 1/15th of the UVB your skin receives, while SPF 35 sunscreen lets through about 1/35. 

This number is misleading for a number of reasons. One, testing agencies apply a thicker layer of sunscreen. When you use a product, the actual amount you spread on your skin might be lower, leading to less protection. Two, it’s a non-linear scale. Higher numbers do mean that less UVB gets through, but most scientists think that going beyond a certain point isn’t very useful. There’s some debate on this break-point, but both the European Union and the Australian government think it’s somewhere below 50.

Most importantly, SPF doesn’t measure how well sunscreen protects against UVA radiation, which is extremely dangerous to your skin. There’s no regulation of the “full spectrum” label either, meaning that your “full spectrum” sunscreen might not do what you think it does. If you want to protect yourself from UVA, look for a PFA rating on the label (it’s more or less SPF but for UVA) or titanium dioxide and zinc oxide in the ingredients.

Myth 2: Sunscreen Lasts All Day

SPF tests are done immediately after a product is applied. If you apply sunscreen and immediately go outside, the number is pretty accurate. Sunscreen’s effectiveness goes down over time, and experts suggest that it’s effective for approximately two hours in the sun. The process in which most sunscreens work, involves your skin to absorb the active ingredients. If you sweat, swim or otherwise get wet, the effective period is even shorter. Be especially aware of “water resistant” sunscreen. It won’t last for much more than an hour if you swim.

Myth 3: Sunscreen Doesn’t Expire

While it’s tempting to keep using the same sunscreen summer after summer, the active ingredients decay. It’s sensitive to heat, light and exposure to air. Kept closed in a cool, dark container, you can probably get away with three years without losing too much effectiveness. If you leave it open on the seat of your car, you might want to replace it a little more often than that.

Myth 4: Sunblock Blocks The Sun

In some places, sunblock refers to an opaque sunscreen with a combination of titanium dioxide and zinc oxide. These physical ingredients are effective at blocking both UVA and UVB light and are not absorbed by your skin, meaning they will protect you all day. In the US, however, “sunblock” doesn’t mean anything. The FDA has banned the use of the term in products and marketing because they think it’s misleading. They feel like consumers would think that sunblock literally “blocks” the sun and will protect them completely.

What These Myths Mean For You

If you want to make the most out of your sun protection, get something affordable above SPF 30. Look for ingredients that block UVA light, or a PFA rating to ensure that your skin is safe from all types of radiation. Re-apply your sunscreen every couple hours when you are out in the sun, and make sure to store your sunscreen in a cool, dark place that doesn’t reach hot temperatures. Replace these products every couple of years to ensure the active ingredients stay at their full potential. By choosing the right sunblock and storing it properly, you’ll get the most out of its protective abilities, and keep your skin healthy and safe from the sun’s harmful rays.

Written by Leah LaVanway