The simple logic behind wearing sunscreen is this: You apply it, you prevent sunburn. But if you glance at any two sunscreen labels, you’ll instantly understand that no two formulas are alike— when you start incorporating things like UVA/UVB/Broad Spectrum, PA++++, SPF, mineral vs chemical, and so forth, it can get a little convoluted. (To say nothing of how it actually feels on your skin, and whether it’s actually waterproof, and whether it makes you look like an out-of-work mime.)
So here’s a general explainer on how to read a sunscreen label to know exactly what you’re getting from any SPF bottle before you get some sun this summer.
What SPF Means
SPF stands for ‘Sun Protection Factor’. The numbers associated with SPF are meant to indicate to the amount of time you can be in the sun while wearing that formula (as opposed to being out sans any coverage) and avoid burning. So a proper layer of SPF 15 would shield you 15 times longer than if you had no SPF at all.
But here’s where those numbers grow confusing: Sure, SPF 30 supposedly covers you twice as long as SPF 15, but that doesn’t have anything to do with how long the stuff stays on your skin in practice. The maximum amount of time you should go between reapplications is 2 hours—or after toweling off post-swim or sweat. In practice, SPF’s effectiveness wanes quickly, no matter how strong it is from the start.
Given this need to reapply often, it’s better to familiarize yourself with each SPF number’s overall defensiveness. SPF 15 will block roughly 93% of UV rays when applied thoroughly. That’s a huge benefit, but a simple upgrade to SPF 30 will shield 97% of rays. It only increases slightly from there. SPF 50 blocks 98%, and SPF 100 blocks 99%. For this reason, professionals recommend you always use SPF 30 as a baseline. You’re much, much better off applying 30 SPF diligently than slapping on some gaudy triple-digit number just once.
Always make sure your sunscreen is broad spectrum, which means it shields you from all types of UV rays.
There are three kinds of UV rays (A, B, and C), but we primarily discuss UVA and UVB rays, since UVC rays are bounced by the earth’s ozone layer.
- UVA rays have the longest wavelength, and thus they’re able to snake into the middle layers of your skin. They’re the ones that cause skin aging, since much of your skin’s firmness, resilience, and elasticity is determined by what happens at this subsurface level. This is also why UVA rays help you tan: They trigger your subsurface melanocytes to produce melanin, and thus turn you darker.
- UVB rays have shorter wavelengths, and they tend to stay on the outermost layer of the skin. They’re the rays that lead to sunburns and that also cause skin cancer.
Typically, UVB rays are deemed the worse of the pair, but any leathery texture, sun spots, and wrinkles can be attributed to UVA rays, so it’s best to block them both.
What About PA+?
There’s a more recent addition to sunscreen labels, in the form of PA+ (with as many as 4 ‘plus’ signs after the ‘PA’). This is short for “Protection Grade of UVA” and is a Japanese rating system that measures how effective a formula is at thwarting UVA rays. That’s because the typical SPF scale determines how long a product will shield you from sunburn—which, given what you learned above, correlates specifically to UVB rays. So, by combining an SPF scale and a PA+ scale, you know what your overall defensiveness is against UVA and UVB rays.