This post will be a summary of everything we’ve learned in the past four weeks. I will also attempt to clear up any confusion, as well as making product recommendations based on skin type.
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.
If you have not yet, please read the separate posts for more detailed information and references on the various characteristics analyzed.
In Part I: Irritation Potential and Aesthetics, we learned that:
- Irritation Potential: OSs tend to be more irritating than iOSs due to a variety of factors, including allergy potential, ease of permeability due to their lipid-soluble nature, and the formation of pro-oxidant degradation byproducts—a result of a lack of photostability, and consequently an increase of photoreactivity—that may or may not cause stinging and/or erythema. OSs also have longer history of more severe allergic reactions such as anaphylaxis, while iOSs like zinc oxide (ZnO) have been shown to even alleviate irritation. iOSs = 1; OSs = 0
- Aesthetics: OSs tend to be more cosmetically elegant than iOSs, since they themselves are translucent off-white colors that don’t reflect light. Therefore, they leave no “white-cast” on the skin, unlike iOSs, which are mineral (pigments) that do reflect light. OS formulations also tend to be less emollient since iOSs require a thicker texture in order to be properly dispersed; it also prevents significant particle aggregation. iOSs = 1; OSs = 1
In Part II: Photostability, Permeability, and Photoreactivity, we learned that:
- Photostability: When OSs absorb UV light, they can undergo two divergent pathways of reconfiguration: a reversible one, and irreversible one. The former means that a particular OS will cycle between various photoisomerizable forms, and since a “cycle” has no end, photostability is achieved. The latter means that a particular OS will form byproducts that cannot be implemented or converted back into its respective “cycle.” Hence, the cycle is broken, and that OS molecule can no longer absorb UV light. And while iOS nanoparticles (NPs) also absorb in addition to scatter light, the rigidity and strength of their crystalline structures allow for increased photostability and structural integrity. Note that, titanium dioxide (TiO2) NPs tend to be less protective than ZnO NPs since the former tends to be smaller in size. Since smaller particles provide less protection than their larger counterparts, that claim certainly has validity and relevancy since many iOSs on the market still don’t utilize nanotechnology. iOSs = 2; OSs = 1
- Permeability: Because OSs are lipid-soluble, they more easily penetrate past the stratum corneum (SC) and come into contact with the living tissue of the epidermis. iOSs, on the other hand, are too large to significantly penetrate past the SC of intact skin. iOSs = 3; OSs = 1
- Photoreactivity: Both OSs and iOSs are capable of generating free radicals such as reactive oxygen species (ROS), and induce oxidative damage such as lipid peroxidation. However, because oxidative damage is only relevant when the UV filters are in contact with living tissue, it appears that iOSs are less photoreactive than OSs, due to a “better” permeability profile. iOSs =4; OSs = 1
In Part III: Toxicity, which was basically a more realized embodiment of the characteristics discussed in Part II, we learned that:
- Toxicity—OS-induced ROS Generation: Over time, the levels of ROS generation from OSs can interfere with important antioxidant enzymes such as thioredoxin reductase, as well as lead to inflammation.
- Toxicity—OS-induced Hormonal Activity or Endocrine Disruption: Some OSs at astronomically high concentrations were shown in vitro to have estrogenic effects. However, in vivo, the amount that penetrates past the SC, the other layers of the skin, and is absorbed into the bloodstream, is very small—significantly lower than what’s necessary to elicit a toxic response. Furthermore, most, if not all, of the systemically absorbed OSs and their intermediate metabolites are rapidly conjugated into glucuronides and safely excreted via urine. It was concluded that OSs do not act as “endocrine disruptors” and are safe for routine use.
- Toxicity—iOS-induced Damage: Like OSs, iOSs can induce oxidative stress, inflammation, and cellular damage. A number of things are done to reduce these problems – adjusting particle size and clumping tendencies as well as choice in morphology, crystallinity, doping, and coating. There is a lot to consider; the overall heterogeneity of iOS NPs makes determining absolute toxicity quite difficult, if not impossible. When it comes to dermal exposure however, except in extreme scenarios (that involve constant motion, prolonged UV exposure, damaged skin, and high concentrations of iOSs), it can be concluded that iOSs are safe because they don’t significantly penetrate past the SC of intact skin, as noted before. When it comes to systemic exposure, for both iOSs and OSs, sunscreen sprays are discouraged to avoid encountering such risks.
- Conclusion: Ultimately, the point was given to iOSs simply because, while iOS NPs are radically more varied than OSs, they appear to have such a safer toxicity profile that I would have to give my vote to iOSs. While neither is anywhere near perfect or even known, the fact that iOSs don’t significantly penetrate the SC and OSs do, makes me more inclined to use sunscreens with inorganic filters, and to consider them as being less toxic. iOSs = 5; OSs = 1
In Part IV: Level of Protection and Practicality, we learned that:
- Level of Protection: Both OSs and iOSs have the potential to achieve virtually equal and excellent levels of protection. Therefore, a point was awarded to each side. It was also noted that in most cases, ZnO is superior to TiO2. iOSs = 6; OSs = 2
- Practicality: Because iOSs are more photostability, their use is more practical, due to having to apply them less frequently. iOSs = 7; OSs = 2
While the final score of (7-2) may seem lopsided, keep in mind that just because a “team” gets a point, doesn’t mean that it’s perfect in terms of that specific characteristic. Furthermore, each characteristic doesn’t necessarily have the same weight or importance. For example, I consider toxicity as being more important than practicality. However, the score does suggest that OVERALL, INORGANIC SUNSCREENS ARE BETTER THAN ORGANIC ONES!! Great! The battle is FINALLY over! Or is it…?
While it’s now been established that iOSs are better than OSs, what about TiO2 versus ZnO? In Part IV, I briefly discussed why ZnO is in most ways better than TiO2. Since then, however, there have been some follow-up questions and lingering concerns about my assessment. So I’ll be briefly discussing this now.
Why Is Zinc Oxide Better than Titanium Dioxide?
Well, as I noted in Part IV, ZnO isn’t always better than TiO2. TiO2 (at a maximum of SPF 38 in the study) was shown to be significantly more adept at attenuating UVB rays than ZnO (reached a maximum of SPF 10 in the study) (13). Keep in mind that while the numbers 10 and 38 are very different, they aren’t THAT different in terms of SPF. Remember that an SPF of 10 blocks 90% of UVB light, while an SPF of 38 blocks about 97%, a difference of about 7%. Still, it’s a statistically meaningful difference.
So there’s just the issue of UVA rays now. As stated in Part IV, this study 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 indicates that ZnO is better than TiO2 at protecting against UVA1 rays, a claim 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. The latter organization doesn’t even consider TiO2 to sufficiently block UVA1 rays.
Some people have noted that both TiO2 and ZnO have similar critical wavelengths (CWs) that are >370 nm. However, while their CWs are quite similar, that method of UVA determination is not valid alone, since the CW is just the 90th percentile of the integral summation or the “area under the curve” of the absorbance function of a specific UV filter in respect (or relation) to itself; it’s a relative rather than an absolute measure of UVA protection.
If you’re familiar with calculus and wondering how two ingredients with the same CW can provide vastly different levels of actual protection, check out this graph. It doesn’t specifically refer to titanium dioxide nor zinc oxide, but the graph will give you an idea of what I’m talking about.
The other half of UVA determination is the in vivo PPD method. This is a measure of the absolute absorbance curve, which, while it hasn’t been widely used yet, is the best model we have so far. It refers to in-part the amount of energy that is transmitted to the skin after UVA exposure.
Now, if you go to the BASF sunscreen simulator, and do any X% TiO2 and X% ZnO estimation (separately) for 2 g/cm^2 and when they’re in a water or oil phase, you’ll see that the Transmitted UV Dose at 1 MED for TiO2 is almost always DOUBLE the amount of ZnO’s. This is because approximately 94% of the sun’s UV rays is comprised of UVA rays. Only 6% is of the UVB variant. If you look at the red line in the last photo of page three of this article from BASF, you’ll see a graphical representation of this concept (note the areas under the red “line” or curve). So while TiO2 provides more protection in the UVB range, it matters less comparatively, seeing as it allows so much UVA irradiation to reach the skin!
Also, if you play around with the BASF simulator, you’ll see that in most cases in the UVA spectrum:
- TiO2 provides more protection from about 320-350 nm than ZnO;
- TiO2 provides less protection from about 350-380 nm than ZnO;
- TiO2 provides similar protection from about 380-400 nm as ZnO.
If you go back to the photo of the BASF article, you’ll see that sunlight is comprised of more UVA rays in the 350-380 nm range, than there are in the 320-350 nm range. And while I acknowledge that the BASF simulator is just that: a simulator, it certainly has merit and significance, not to mention that the BASF database is overwhelmingly massive and pervasively used. All of this, combined with the other studies mentioned in Part IV, only substantiates the claim that, in most ways ZnO is better than TiO2.
However, several other aspects mentioned in the other parts also make me favor ZnO more than TiO2. For example, ZnO was shown to be less “white” than TiO2, due to a lower refractive index. ZnO NPs also tend to be larger in size than TiO2 NPs. Finally, ZnO NPs tend to be less photoreactive than TiO2 NPs.
Nevertheless, protection from UVB rays and UVA2 rays is still VERY important. Therefore, when I make my product recommendations down below (in no particular order), I’ll be choosing products that contain both ZnO and TiO2, preferably with more of the former than the latter; or they contain ZnO with organic UV filter(s) to boost the level of UVB protection.
Also, keep mind that because ROS generation induces and initiates many of the potential negative side effects of both OSs and iOSs; always remember to use antioxidants with your sunscreen! While antioxidants in a sunscreen are good, I typically recommend a separate product to be applied underneath your sunscreen.
Oh one more thing to note, because I live in the United States, I’m only familiar with the products that are readily available over here. Many readers have expressed that they think Asian sunscreens are a lot better than American ones in terms of texture and aesthetics, and I can’t speak on that subject because I personally have no experience with them. However, if you’d like to add a recommendation, please do so down below in the comments section!
SUNSCREENS FOR NORMAL TO DRY SKIN TYPES:
- Clinique City Block Sheer Daily Face Protector SPF 25 (7.3% TiO2 and 6.9% ZnO): I’ve gone through one bottle of this and even for my oily skin type, this wasn’t too bad. It is slightly tinted and provides sheer coverage, though you’ll most likely need concealer for spots and under the eyes. This also contains several beneficial though not necessarily photoprotective botanical ingredients such as the skin-lightening birch extract, and the calming cucumber extract. Overall, this is a good everyday sunscreen that I’d probably still be using if I had dry skin ($22.49, amazon.com).
- EltaMD UV Lotion SPF 30+ (7.5% Octinoxate, 7% ZnO): This is an affordable option for those who aren’t in the sun often and like to be able to just slap on sunscreen, without worrying about having to blend out the white-cast. While I would prefer if this had a bit more ZnO, the price is just undeniable attractive. I have to admit that this provides what I’d deem to be almost below decent/borderline levels of sun protection. So this is definitely not something I’d recommend for people to bring to the beach ($21.50, amazon.com).
- Blue Lizard Baby Suncream SPF 30 (10% ZnO, 5% TiO2): Note that this product is identical to the Blue Lizard Sensitive Sunscreen SPF 30+, which is the “adult” version. On the other hand, this is something I would bring to the beach to apply all over the body (except the face). I’ve gone through a bottle of this, and it leaves a slightly greasy residue and white-cast. I personally hate applying this, but I’d imagine that for someone with a drier skin type, this will be a godsend! I believe Dr. Leslie Baumann, the renowned dermatologist, uses this as her daily sunscreen ($19.54, amazon.com)
- PCA Skin Perfecting Protection SPF 30 (9.8% ZnO, 7.5% Octinoxate): While pricier than the other options, this is an acceptable choice for those who do not wish or don’t have the time to apply an additional antioxidant serum. To enhance photoprotection, this contains a vitamin E ester, as well as the Silybum marianum extract, which has been shown in multiple studies to strongly prevent UVB-induced immune suppression, oxidative stress, and DNA damage by inhibiting the formation of cyclobutane pyrimidine dimers (CPDs). It also contains some botanical skin “brighteners” such as kojic acid, and the mulberry and licorice extracts. Overall, it’s an interesting formulation with a tad of denatured alcohol/ethanol thrown into the mix to solubilize the ingredients, and fluidize the texture ($19.50, amazon.com).
SUNSCREENS FOR NORMAL TO OILY SKIN TYPES
- Shiseido Ultimate Sun Protection Cream SPF 55 (16.3% ZnO, 7.4% Octinoxate, 2.2% TiO2): This is what I’ve been using for the past year or so. There are several pros and cons to this product. While it provides very good protection, the white cast that it leaves is so apparent, even when I mix a bit of foundation into it. I must have gotten at least a dozen comment from friends either saying I’m as white as Edward, or that I should go back indoors before I catch on fire… It’s always something along those lines. This just isn’t very easy to use. I have to spend a lot of time blending. Once it dries though, it lasts like iron; even my oily skin doesn’t put it a dent in it after 12+ hours. However because of that, the finish is slightly tacky and at the end of the day, it takes several cleansings to remove completely. Overall, it’s a superior sunscreen that unfortunately, is both difficult to apply and remove. To me, I’d rather use something a bit simpler on a day-to-day basis, which brings me to the next product ($29.85, amazon.com).
- EltaMD UV Clear SPF 46 (9% ZnO, 7.5% Octinoxate): This is for someone who prefers something less thick than the next product, while still providing decent protection. It isn’t very water-resistant but it sits a bit more pleasantly on the skin, due to its silicone base. There’s also a good amount of niacinamide, which while not having any photoprotective characteristics, is anti-inflammatory, and skin lightening ($18.99, amazon.com).
- EltaMD UV Pure Broad-Spectrum SPF 47 (10% ZnO, 5.5% TiO2): The texture of this is very thin. It’s also quite water- and transfer-resistant. It doesn’t provide as much protection as the Shiseido, but is still quite good ($19.39, amazon.com).
- PCA Skin Active Very Water Resistant SPF 45 (8% ZnO, 7.5% Octinoxate, 3% Octisalate): This is the PCA Skin version of the Shiseido and EltaMD water-resistant sunscreens. Like its cousin that I mentioned above, this is appropriate for those who don’t have time to apply another product underneath this one, and are okay with using something that only provides acceptable levels of sun protection. It contains good amounts of the powerful Silybum marianum extract, as well as a vitamin C ester, though ($23.01, amazon.com).
For an extensive and updated list of sunscreens that I’d recommend, make sure to tune in my blog, when I publish the Ideal Routine and Sun Protection Pages. Here’s the publishing schedule.