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Are Inorganic Sunscreens Better Than Organic Ones? Part IV: Level of Protection, and Practicality

Slap on that sunscreen!
Since our post on toxicity last week was so tedious, I’ve decided to keep this one relatively short and sweet. Okay, it’s more that there aren’t too many conclusive articles specifically pertaining to these characteristics! ***In this series, I will refer to inorganic sunscreens as iOSs (not Apple, mind you) and organic sunscreens as OSs. While there are many individual compounds in each group—particularly OSs, for the purposes of this post, I will only refer to individual iOSs and OSs as parts of their respective groups. Complete and comparative ingredient profiles will not be seen in this series. Furthermore, I will attempt to discuss technologies that are more relevant and reflect the sunscreen technologies and tendencies of the current market. For example, while para-aminobenzoic acid (PABA) has many documented negativities, it will be ignored in our discussion, due to the fact that it is hardly used nowadays in sunscreen formulations.

Level of Protection

Sun protection comes in many forms!
These days, because adequate protection against UVB rays is virtually guaranteed, I’ll mostly be focusing on protection against UVA rays. For OSs, the two readily available ingredients (in the US) are oxybenzone and avobenzone, with the former protecting against UVA2 rays, and the latter protecting against UVA1 rays. Both, when properly formulated and stabilized, provide excellent protection. On to the iOSs: the biggest “controversy” or question that I get asked is whether or not zinc oxide is better at absorbing UVA1 rays (>340 nm) than titanium dioxide. So that will be the primary focus of this section. To start off, the answer is a resounding YES! IN MOST WAYS, ZINC OXIDE IS BETTER THAN TITANIUM DIOXIDE
Zinc oxide is the winner! Usually. This is the wurtzite crystallization structure.
Various studies have indicated that ZnO is better than TiO2 at protecting against UVA1 rays. For example, this study (1) demonstrated that both (3%) avobenzone and (5%) ZnO increased PFA values by nearly 3-fold when added to 6% oxybenzone; 18.2 and 16.0 respectively. Titanium dioxide at various concentrations (2.4%-9.1%) and with or without oxybenzone, only increased PFA values marginally (8.4-10.5). This is further supported by the fact that in the past, both the FDA and the Skin Cancer Foundation have not recognized TiO2 to provide adequate protection against UVA1 rays. In fact, the latter doesn’t even consider TiO2 to block UVA1 rays (3). However, it is known that TiO2 does provide some protection in the UVA1 range; it does well against UV rays that are < 350 nm. Keep in mind that the PFA values were determined via the delayed erythema method, which may be used interchangeably with the persistent pigment darkening (PPD) method. The results from both of these methods are considered comparable (2). However, some have claimed that when formulated properly, TiO2 will provide adequate UVA1 protection and specifically, will satisfy the critical wavelength test of providing protection against UV rays that are >370 nm. This qualification is one of the rules that the FDA plans to implement and enforce beginning December, 2012.
FDA = the BIG tamale.
While the FDA is very rigorous when testing the safety and toxicology profile of a UV filter, it's not so stringent when it comes to HOW MUCH protection is seen. Yes, TiO2 does provide some protection beyond the critical wavelength of 370 nm, but it doesn’t provide nearly as well as ZnO in that range. However, if you still insist on using just TiO2 to provide full UVB, UVA2, and UVA1 protection, then that is your choice. But as study (2) suggests, the difference in protection is not as small as previously thought. Study (4) further substantiates this claim, in addition to acknowledging that ZnO is less “white” than TiO2 due to the former (2.0) having a lower refractive index than the latter (2.6). However, in terms of UVB protection, TiO2 is significantly better than ZnO! This study (5) suggests that ZnO can’t achieve an SPF of higher than 10, while TiO2 reached an SPF of 38. While these numbers aren’t absolute, they do support the above mentioned claim. Like I said, there are pros and cons to ZnO and TiO2. Overall and for the first time ever, I’m going to award both sides a point each, just because exact levels of protection will vary based on a variety of factors; many of which were discussed in parts II, and III. But relatively speaking, both iOSs and Oss can provide excellent levels of protection. iOSs = 6; OSs = 2


Please reapply sunscreen when necessary!
This will be about the need of reapplication and how practical that application is in terms of iOSs and OSs. Reapplication is deemed necessary for two reasons: one, because UV filters degrade upon irradiation; and two, the sunscreens might be wiped off, sweated off, and/or otherwise removed. In terms of photostability, as we noted in part II, iOSs are more stable than OSs. However, at a nano-scale level, it was also noted that iOSs begin to act as semi-conductors and absorb as well as scatter UV light. Therefore, they aren’t completely stable and reapplication is necessary… in certain situations. If you’re going to a place where you expect to constantly be direct sunlight, then reapplication every two hours is necessary, and more frequently if you’re swimming. However, on a day-to-day day basis, if you’re wearing sunscreen under makeup and aren’t outdoors for a long period of time, it isn’t practical to take off your entire face and reapply everything. So in this sense, because iOSs are more stable than OSs, the former group is more “practical;” because iOSs need to be less frequently reapplied, if at all, on a day-to-day basis. What about the sunscreen being removed factor? Well, that doesn’t really depend on the UV filters themselves. Rather it’s mostly the vehicle that determines how transfer-, water-, and/or sebum-resistant a sunscreen is. While OSs can help make a product more water-resistant due to their lipophilic nature, there are other ingredients that can be incorporated into a iOS to function in a similar fashion. Therefore, in terms of this, I’d say both groups are tied. For this somewhat subjectively evaluated characteristic, I’d give the point to iOSs because, while stabilized OSs can work just as well as iOSs, many products on the market are not stable. And the ability to stay on the skin or to not be removed, depends more on the vehicle rather than the specific UV filters, which is independent of sunscreen type. Therefore, iOSs have a slight edge over OSs. iOSs = 7; OSs = 2

We’re done! Finally!

This concludes the (mostly) evidence-based interpretation of why I think iOSs are better than OSs. For the final part next week, I will summarize all the major points of each post written thus far, and make product recommendation based on elements such as skin type, level of protection, and many other aspects! So keep checking back! While you’re waiting, join in the lively discussion on my blog asking, “What type of product do you think is still missing on the current market?” And of course, you can let me know what you think of this post, too! Link/References:
By: John Su
Date: September 6 2012 at 11:03 AM
Q&A, Skin Care, avobenzone, better, critical wavelength, john su, nanoparticles, practicality, reapplication, sunscreen, titanium dioxide, uva1, zinc oxide

Comments (8)

  1. janine
    September 7 2012 at 4:54 AM

    Again, thank you for shedding so much light onto what has become a very confusing topic. I truly feel that this topic is worthy of a 5 part series and will eagerly await next week's post. Just to be clear, though.........are you saying that there is no actual set "time" factor for degredation after application (i.e. 2 hours for iOS and 4 hours for OS which, for some reason, was always what i thought it was). But rather it is the surrounding circumstances like time spent in direct sunlight and possible removal due to sweat, swimming, etc? I just want to be clear because i go to great lengths to reapply my iOS in the late afternoons after spending all of the daylight hours indoors at work.

  2. John Su
    September 7 2012 at 11:00 AM

    @janine You're welcome! And unfortunately, there IS no set time factor of degradation, because they can vary so greatly. For example, even in the study that I cited (1), avobenzone was shown to degrade 90% after 4 hours of UVR exposure. The addition of 10% octocrylene maintained the chemical structure of avobenzone virtually intact, while 6% oxybenzone maintained about 70% of the avobenzone after 4 hours. Octisalate (5%) and homosalate (12%) were much less effective, but still provided modest protection of the avobenzone. And while iOSs nanoparticles tend to be more stable, they are still not completely so, as shown in the various posts. And yes, sunscreens need to be reapplied if they're removed, or degraded. Many professional skin organizations such as the American Board of Dermatology, etc., simply recommend reapplication every 2 hours to cover all the bases. Not to mention that most people don't apply enough sunscreen, so the act of reapplication can boost the amount of sunscreen applied in order to achieve more adequate protection. However, it is my personal opinion, at least for high % iOSs, is that if you're indoors (and when you're inside, there isn't much sunlight either because there are no windows, or the blinds are shut) reapplication is not necessary if you can still feel most of the sunscreen on your face. That's why I use a budge-resistant sunscreen; I can still feel it on my skin 12+ hours after initial application. But the fact that you go to great lengths to reapply your iOS, is commendable! I can't imagine how you do that, since I think you said that you wear foundation, and I'd imagine a setting powder over it. Do you remove everything and then reapply? But depending on whether or not there is much UV exposure when you're indoors and how much sunscreen you intially apply, reapplication may not be necessary. But hey, if you've got a relatively easy reapplication routine down, keep at it. If you're used the routine, then you might as well. That way you're ensuring more protection. I just don't have the time nor care to reapply when I'm indoors without much (maybe <5%) natural sunlight. and i think that works well for me, seeing that i can maintain my natural nc15-nc20 even in the summertime. :) if i'm going to the beach, which in fact, i never do, or anywhere outdoors for a long time, then i do reapply when i can. i hope that made sense, and if you have further questions, please don't hesitate to ask! natural="" sunlight.="" and="" i="" think="" that="" works="" well="" for="" me,="" seeing="" that="" i="" can="" maintain="" my="" natural="" nc15-nc20="" even="" in="" the="" summertime.="" :)="" if="" i'm="" going="" to="" the="" beach,="" which="" in="" fact,="" i="" never="" do,="" or="" anywhere="" outdoors="" for="" a="" long="" time,="" then="" i="" do="" reapply="" when="" i="" can.="" i="" hope="" that="" made="" sense,="" and="" if="" you="" have="" further="" questions,="" please="" don't="" hesitate="" to=""></5%) natural sunlight. and i think that works well for me, seeing that i can maintain my natural nc15-nc20 even in the summertime. :) if i'm going to the beach, which in fact, i never do, or anywhere outdoors for a long time, then i do reapply when i can. i hope that made sense, and if you have further questions, please don't hesitate to ask!>

  3. janine
    September 10 2012 at 7:36 AM

    nice memory on the foundation wearing, young sir............and I'm glad you brought that up because my follow up quesiton relates to my answer on that issue: my re-application method of sunscreen is currently brushing on the Colorscience Pro Sunforgettable before leaving the office. However, i have read here on Nicki's sight that brush-on sunblocks aren't worth the time or money. Your thoughts?

  4. John Su
    September 10 2012 at 5:38 PM

    @janine Well, I think it can't hurt. Just be careful not to inhale any. Whenever I apply loose or pressed powder, or hairspray, etc... I always hold my breath and run out of the bathroom when I'm done. Haha! Lame I know, but it's true. But yeah, while I don't think the Colorscience product is worth the high price tag, it certainly will increase UV protection. It may not be much (since you have to apply a TON of powder to achieve a nice thick coat), but it's still better than nothing. But like I said before, as long as you can feel the sunscreen and it's an iOS, for everyday purposes, a water-resistant formulation like the EltaMD SPF 47 (which I think you use) doesn't need to be reapplied and will provide adequate protection throughout the day. Of course, that's assuming that when you're indoors, there isn't much UV transmission, and you're not excessively oily or sweaty.

  5. belgianred
    September 10 2012 at 8:01 PM

    Thanks for doing all this work! I've been confused about the 2-hour rule for a while. It sounds like you're saying that's 2 hours of UV exposure, rather than 2 hours of wear? Say you spend an hour in full sun, 4 hours in an office cubicle or a cave, and then go back out into the sun without having sweated you need to reapply? Are any of the ingredients unstable in air, in addition to becoming unstable in UV? (I mainly use a zinc/titanium combo, although I'd like to try tinosorb.) Another rule that I don't understand is the one about applying sunscreen 15 minutes before UV exposure. Do you know why, and how important this actually is? Thanks!

  6. John Su
    September 11 2012 at 5:43 PM

    @belgianred Like I said to janine above, the 2-hour rule is just to cover all the bases: One, a lot of sunscreens aren't very photostable, so reapplication would replenish degraded UV filters; Two, they aren't very transfer-resistant, so reapp will again replenish "removed" sunscreen; Three, in case people wipe off or sweat off the sunscreen, so reapp will again replenish; Four, most people don't apply the adequate 2 g/cm^2 amount, so reapplication will increase photoprotection. But if you and your sunscreen fulfill all of those requirements, then yes reapplication may not be necessary. Although if you can, it can't hurt to do so. . Now, your scenario of one hour of full sun, etc... means you won't have to reapply if it's an iOS, and you fulfill the requirements above. This can even apply to some OSs. But since they more widely vary in terms of photostability (based on the formulation), I don't feel comfortable including them in this broad statment. Keep in mind that the 2-hour rule doesn't mean that all sunscreen will be gone in 2 hours. It's just to (again) cover all the bases. And no, sunscreens aren't meaningfully degraded by exposure to air. (Think about the manufacture process). Though if it can be avoided, that's good. The 15-minute rule, is just another "cover-all-the-bases" move. The 15 minutes will help the sunscreen vehicle set and be less prone to being wiped off, etc.. And it also allows for the UV filters themselves to form a more even layer on the skin in order to provide adequate protection. OSs typically need more help in this department since they're so large in size, so time is more of a necessity in order for them to settle properly. I hope that makes sense. I'm totally blabbering haha.

  7. Nicholas
    April 6 2013 at 10:20 AM

    Hi Jonh, I love the blog! I have been really curious about the La Roche Posay Mineral spf 50 that's 11% titanium dioxide. It claims a PFA of 21 and I really like the product. I think lots of people are skeptical of how they obtain the PFA of 21 but they claim it's the dispersion and size of the particles in the emulsion. What are your thoughts on this? Thanks, Nicholas

  8. John Su
    April 7 2013 at 7:50 PM

    @Nicholas Thanks! Actually, it's impossible for titanium dioxide or zinc oxide to achieve a UVA-PF rating of anywhere near 21 at 11%, especially not across the entire UVA spectrum. In fact, even 25% TiO2 (the maximum concentrations allowed in sunscreens; you'll look like you're wearing a white mask) cannot achieve such a rating. So yeah as far as I'm concerned, it's a lie or at the very least, an omission of truth.

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