Written By Mira Aguirre
Article Summary
- What is mineral sunscreen?
- Inorganic vs organic UV filters
- Limitations of zinc oxide
- Mineral sunscreen myths
Sensitive skin? Pregnant or breastfeeding? Experiencing hyper pigmentation? Chances are, you’ve been told to use mineral sunscreen.
Zinc oxide and titanium dioxide based sunscreens are often touted as the safest, most protective, and environmentally friendly options for sun protection. Today, we’re investigating these claims and finding out the truth.
What is Mineral Sunscreen?
Mineral, physical, inorganic. These are all interchangeable terms to describe the ingredients zinc oxide and titanium dioxide that are used in mineral sunscreens. In this blog, we will either use the specific names of these sunscreen agents or use the term “inorganic UV filters” as this most accurately describes them on a chemistry level.
Inorganic substances don’t contain carbon in their structure. Zinc oxide and titanium dioxides are a perfect example of this as they’re both metal oxides - substances made from metals and oxygen. Another example would be iron oxides, an ingredient used in makeup like foundation to add a tint while also offering some protection against visible light exposure from the sun.
Now, inorganic UV filters alone don’t make a sunscreen. They need to be properly suspended in a base and there’s a lot of other ingredients used to help in optimizing protection, creating a nice application experience, and keeping the product stable. We’ll talk about formulation challenges later but for now, just know that purely mineral sunscreens should only contain zinc oxide and/or titanium oxide.
Like most metal oxides, zinc oxide and titanium dioxide are insoluble. That means when you add them to water or oil, they don’t dissolve. As a result, they have to be suspended within a sunscreen product. A good way to visualize this is to imagine filling a cup with equal parts oil and water. Left alone, the oil remains fully separate. Take a whisk and blend just a little and you’ll see oil droplets floating in the water - or you can continue to mix until the droplets are so small, it looks like the oil and water are combined to the naked eye. That’s essentially what we’re doing with inorganic UV filters, we’re dispersing them in the sunscreen as evenly as possible.
Zinc oxide is broad spectrum, meaning it protects against the full spectrum of UV light we are exposed to from the sun, while titanium dioxide protects against UVB radiation and part of the UVA spectrum. When zinc oxide is used alone or in combination with titanium dioxide, it’s possible to formulate a broad spectrum sunscreen with a high level of protection. We’ll get into the limitations and drawbacks next but it should be stressed that there are excellent mineral sunscreens available on the market.
Organic vs. Inorganic UV Filters
Now, let’s talk about organic UV filters. These are the sunscreen agents used in what many call “chemical sunscreens.” This isn’t the most accurate term (everything is a chemical) so I like to call them organic sunscreens instead. These UV filters contain the element carbon in their structure - remember, zinc oxide and titanium dioxide do not. In terms of their chemical structure, most of them have an aromatic ring and a carbonyl group, allowing them to absorb sunlight.
Commonly Used Inorganic UV Filters
Zinc Oxide
Titanium Dioxide
Commonly Used Organic UV Filters
Avobenzone
Homosalate
Octocrylene
Octinoxate
Octisalate
Oxybenzone
Padimate O
Ensulizole
Common UV Filters Not Approved in the US
Tinosorb S Bis Ethylhexyloxyphenol Methoxyphenyl Triazine
Tinosorb M Methylene Bis-Benzotriazolyl Tetramethylbutylphenol
Uvinal A Plus Diethylamino Hydroxybenzoyl Hexyl Benzoate
Uvinal T-150 Ethylhexyl Triazone
Mexoryl SX Terephthalylidene Dicamphor Sulfonic Acid
Mexoryl XL Drometrizole Trisiloxane
Mexoryl 400 Methoxypropylamino Cyclohexenylidene Ethoxyethylcyanoacetate
TriAsorb Phenylene Bis-Diphenyltriazine
Parsol SLX Polysilicone-15
Uvasorb HEB Diethylhexyl Butamido Triazone
Different UV filters have different spectrums of UV light that they absorb so you’ll generally see a combination of them used to ensure broad spectrum protection. There are a few, like Tinosorb S or Tinosorb M, that are broad spectrum but still used in combination with other filters. This is because sunscreens also need to provide a certain amount of UV absorption and it can sometimes be difficult to get that from a single filter when brands must adhere to max usage rates.
What are the actual differences between organic and inorganic UV filters that you should be aware of? Unless there’s a specific reason you can’t use one or the other, there’s no reason to avoid them. All that matters is that you have a sunscreen that works for you. Sometimes, sensitive skin types do better with mineral sunscreens since organic UV filters penetrate more into the skin (though they are formulated to remain on the surface). But the newer filters available outside the US have less penetration so this doesn’t apply to them as much. Aside from some differences in the application of the product that we will dive into next, there’s no other real differences you need to worry about.
Limitations of Zinc Oxide
Zinc oxide is often touted as the #1 sunscreen ingredient you can use. It offers broad spectrum protection and because the FDA allows it to be used in concentrations up to 25%, it can even serve as the sole UV filter in a sunscreen. While there is nothing wrong with using zinc oxide based formulas if they work well for you, they have a number of drawbacks and can discourage others from using sunscreen when they’re told this is the only option.
- Zinc oxide has low UV absorption. Compared to other UV filters, a lot of zinc oxide needs to be packed into a formula to get SPF 50 or even SPF 30.
- Zinc oxide (and titanium dioxide) aren’t soluble. As a result, packing 20% or more into a sunscreen to get decent protection is no easy task and this can often result in a product that isn’t very cosmetically elegant to apply. Because you’re dispersing an insoluble powder into a base, there can also be gaps in your protection when applied to the skin if it’s not properly distributed.
- Inorganic UV filters leave a cast. Titanium dioxide is even used as a white pigment so these types of UV filters are not transparent and will leave a cast, despite brands claiming that they are “sheer.”
- Zinc oxide isn’t quite broad spectrum. While it offers protection against UVB and UVA radiation, the protection is quite low as we reach the portion of the UV spectrum with the longest UVA waves. And unfortunately, titanium dioxide is even worse here.
So how do brands and their cosmetic chemists solve these issues?
- Particle size is one answer. Zinc oxide and titanium dioxide nanoparticles have less white cast and you don’t have to use as high of a concentration in a sunscreen formula. This also increases the solubility in oil so there’s some - like BASF’s Z-Cote) that are soluble in oil. However, this isn’t a perfect solution because nanoparticles do have a slightly different absorption spectrum and UVA absorption can be reduced.
- Lately, formulation. Dibutyl Adipate is just one example of an ingredient that helps solubilize UV filters and improve spread. There’s a lot of “helper” ingredients that influence the texture and application of a product as well as its protection.
Note: some brands use SPF boosters like butyloctyl salicylate. While there’s nothing wrong with this ingredient, its chemical structure is similar to organic filters like octisalate and it too absorbs UVB light. It just can’t be called a sunscreen ingredient because it isn’t approved for that purpose. As a result, brands will use it and still call their product a mineral sunscreen.
Mineral Sunscreen Myths
Let’s wrap this up by debunking some common myths you may have come across. Many of these are used to argue that inorganic UV filters are better and it’s important to have all the facts so you can make an informed choice when shopping for sunscreen.
#1 Mineral sunscreens reflect UV light so they are better for melasma because they don’t absorb UV light and release it as heat.
Myth. As we discussed above, both times of UV filters work primarily by absorption. That means they absorb UV light in their excited state and then convert it to heat which is released during their ground state.
#2 Zinc oxide is better for hyper-pigmentation because it reflects light, including blue light.
Myth. Not only does zinc oxide only reflect a small amount of UV light but as we discussed above, it doesn’t offer much protection against long wave UVA radiation and none against blue light. These wavelengths do tend to trigger hyper pigmentation but it’s actually the iron oxides added to help with the white cast that are helpful.
#3 Mineral sunscreens are better for sensitive skin.
Myth, sorta. It’s true that some sensitive skin types do better with mineral sunscreen and they can cause less eye sting if a lot of sunscreens sting your eyes. But there’s no reason to avoid organic sunscreens if your skin is tolerating them fine and the newer organic filters used in your countries are often sensitive skin friendly.
#4 If you’re pregnant or breastfeeding, you should only use mineral sunscreen.
Myth. Essentially, we just don’t know one way or the other as neither category of sunscreen agents is well researched. While the risk is low compared to the very real risks of sun exposure, we recommend discussing this with your OBGYN instead.
#5 You don’t need to reapply mineral sunscreens.
Myth. While it’s true that older organic UV filters tend to be less stable, there’s still a lot that chemists can do to stabilize them. And ultimately, it’s often the breakdown of the sunscreen film on the skin that requires reapplication, not the instability of the UV filters.
So what should you take away from this? At the end of the day, the best sunscreen is the one that you’ll use. The point of this blog isn’t to sway you in either direction, but to show that both inorganic and organic UV filters are safe and effective. Rather than avoiding one or the other, look for a sunscreen that applies nicely and offers great protection.
References
Mira is a skincare educator, blogger, and the content creator behind Skin Science by Mira and The Skincare Forum on Facebook. While skincare keeps her busy, she’s also pursuing her degree in Nursing and loves to spend her free time hiking. As a content writer for Stratia Skin, Mira shares her evidence-based approach to skincare topics and a passion for making science accessible.
