When it comes down to it, there are two types of sunscreen: chemical and physical. Chemical sunscreen is loaded with various actives (e.g. avobenzone, oxybenzone, helioplex) that chemically bind to skin and absorb (some scatter) UVRs- defusing that energy as heat. Physical sunscreen on the other hand is made up of two actives (specifically: titanium dioxide and zinc oxide) that act like a physical barrier- reflecting and repelling UVRs. However, titanium dioxide and zinc oxide don't just reflect light, they also attenuate UVRs- just like chemical sunscreens. Only about 10% of the UV energy is scattered.
Due to the way chemical sunscreen acts with the skin, it needs to be applied 30 minutes before you're protected. Physical sunscreen, however, acts as a barrier immediately.
Now neither option is perfect nor is one necessarily better than the other. A con to chemical sunscreens is that some filters generate free radicals when interacting with the sun, potentially damaging DNA. Physical sunscreens do not cause free radicals. Furthermore, chemical sunscreens can often be more irritating to sensitive skin- in fact this irritation is precisely why many people opt for physical sunscreens over chemical ones. A con for physical sunscreens, however, is the often garish white cast they leave behind post application. Moreover, physical sunscreens don't offer as much UVA protection as a chemical sunscreen would. Chemical sunscreens need to be reapplied every 2 hours, as they aren't photostable and therefore degrade in sunlight; whereas physical sunscreen is (postulated to be) protective as long as it's intact (which could be all day). However, it's still suggested to reapply frequently- especially if you're swimming or you've been perspiring heavily.
The mix of pros and cons to each is why you'll often find sunscreens as a mix of both physical and chemical.
When judging the efficacy of sunscreen, a lot of people go by SPF ratings and that's it. Unfortunately you're only getting half of the story. SPF stands for sun protection factor and it measures how much UVB protection you're getting. UVA protection, on the other hand, isn't quantified and listed for US sunscreens. You can guesstimate how much protection you're getting based on the ingredients (some people even judge UVA efficacy of sunscreen by color changes in the skin), but I really advise you not do that. As you learned in our previous installment of Why You Need Sunscreen, UVBs burn and UVAs don't. So by the time you see changes in color to your skin- it's entirely too late. The damage has been done. You can't rely on physical clues alone to let you know the kind of protection you're really getting. Instead, I advocate buying... abroad.
Asian and European sunscreens are required to measure and list UVA protection. They do this through the PA and PPD system respectively. Unfortunately, a minimum amount of PA/PPD protection hasn't been agreed upon (mostly due to the utter complexities of UVA in general). Thus I advise you use the highest PA/PPD you can afford/you find comfortable.
To receive the labeled protection, you need to apply 2 mg/cm2 (this is for everything- sunscreen, sunscreen sprays, makeup, powder, or lotion). This amounts to about 1/4tsp for the face alone- 1/2tsp for the face and neck. And 1 ounce for your entire body. Unfortunately, you'll never be able to block 100% of the UVRs raining down on you. So you might be tempted to go for the highest SPF you see and deem that perfect- maybe even decide that you don't have to apply the entire amount you need to. First of all, when you apply half as much (for example, 1 mg instead of 2), your protection doesn't go down by half (SPF 100 down to SPF 50), instead protection plummets in an almost square-rooted fashion (SPF 100 down to SPF 10).
Moreover, many doctors/experts think anything above SPF 45 is ridiculous- since SPF 45 blocks 98% of UVBs. There's even a proposal to change SPF labeling in America of anything above SPF 50 to SPF 50+. It's manipulative to limited consumer knowledge to sell SPFs higher than 50, principally because SPF doesn't increase in efficacy multiplicatively. SPF 30 is not 'twice as protective' as SPF 15, it's merely a small percentage better- increasing from 94 to 97 percent. And as I've said before, you'll never be able to block 100% of UVRs (so can you see how manipulative higher numbers are to those who aren't educated in sunscreen?). This sweet little bar graph illustrates UVB protection with SPF. As you can see, even an SPF of 2 is better than absolutely nothing.
So you've settled on a chemical/physical mix SPF 30, PA++ sunscreen and you're applying it daily. It absorbs quickly, there's no white cast, and dammit do you just love it. Well, what about vitamin D, I hear you asking. Lucky for you, there's evidence that sunscreen doesn't impact vitamin D production in the skin enough to cause a deficiency; however, a simple blood test at the doctor's office can help you determine for sure if you need supplementation. If you're still worried, a multivitamin is a great option. In rare instances, Vitamin D toxicity can cause excessively high amounts of calcium in the blood, but for the most part you won't be receiving this much vitamin D in a multivitamin. More common side effects (when way too much is taken) are weakness, fatigue, headache, and so on.
What about the sun making me feel all googly happy- I have Seasonal Affective Disorder and need to get sun! I hear you cry. No, my dear reader, what you need is visual sun. While the exact mechanisms are unknown, many causes of SAD have been proposed and nearly all of them have to do with the neurotransmitters released, visual pathways in the brain (e.g. the retinohypothalamic tract and the suprachiasmatic nucleus) and circadian rhythm. This is why light therapy is so successful when treating SAD and psychoactive drugs that treat depression are also successful- they target the same neurotransmitters that cause 'regular' depression. So while it may feel amazing to stand in the sun, you don't need to stand in it unprotected to reap its benefits. Just seeing the light is enough. And trust me, I live in Southern California- I know how amazing the warm sun feels on the skin. Luckily it feels just as amazing and warm when there's a layer of sunscreen protecting my delicate skin.
So that's the nitty gritty on sunscreen (and vitamin D and your brain, haha). If you have any questions please leave them below in the doobly doo and I will get to them ASAP- and I'll add further detail in this post if your question requires further information here, too. You can even ask about more detail on circadian rhythms and your brain. I have loads of textbooks discussing physiology and I'm not afraid to start quoting/sourcing for you.
Until next time, Hoojoo fans.
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