Understanding SPF Boosters in Mineral Sunscreens: Unveiling the Truth Behind Zinc Oxide Concentrations
Introduction:
Looking at the connection between SPF boosters in Mineral Sunscreens
Pick up your all-mineral sunscreen and you'll see formulas with 25% zinc oxide and some with 2% zinc oxide. Why is there such a range or difference between different formulas? Can 2% zinc oxide ever be the same as 25%? Most consumers focus on the labelled SPF of a product and if both concentrations of the UV filter can give similar SPF’s then clearly there is no meaningful difference between the 2% vs the 25%. And then SPF boosters enter the chat.
Sunscreen chemistry is arguably the most complicated within the personal care and beauty space. Unlike for example your favourite moisturizer, the safety of your sunscreen is tied to its efficacy. If it does not perform well, it's not safe. This means that it's a high stakes question when we start to ask why some sunscreens have low amounts of a UV filter versus why some have much higher concentrations.
To begin to understand this essential question, we compiled a database of commercially available sunscreens looking at their labelled SPF and their active and inactive ingredients. We focused our analysis on 'all-mineral' sunscreens that listed zinc oxide as their only active ingredient so that we could compare UV filter efficiency easily.
We then sorted these into 4 groups based on their labelled concentration of zinc oxide as the active ingredient and their labelled SPF.
Group 1 (low zinc oxide/ low-moderate SPF): sunscreens with less than 15% zinc oxide and SPF 35 or less
Group 2 (moderate-high zinc oxide/ low-moderate SPF): sunscreens with 15% or more zinc oxide and SPF 35 or less
Group 3 (low zinc oxide/ moderate-high SPF): sunscreens with less than 15% zinc oxide and SPF 36 or more
Group 4 (moderate-high zinc oxide/ moderate to high SPF): sunscreens with 15% or more zinc oxide and SPF 36 or more
Our goal was to look at the correlation between the use of SPF boosters butyoctyl salicylate, tridecyl salicylate, and bisabolol within these 4 groups. Our hope was that we could discern some key trends when it comes to zinc oxide concentration, SPF and SPF boosters. Do sunscreens that contain low amounts of zinc oxide but have disproportionally high SPF's have something in common? The data shows some key and concerning links between low UV filter concentration and the use of SPF boosters.
Background:
Consumer Confusion around UV Filters and Concentration in Sunscreens
Let's get straight to the point. There is mass confusion in the sunscreen industry when it comes to a basic question.
Does it matter how much of an active ingredient is used in your sunscreen formula? Or put in other terms, does the concentration of your UV filter matter? It's a question for all sunscreens but also relates to the issue at hand regarding all-mineral sunscreens with low concentrations of actives.
It's definitely a complicated question. Instead of admitting to the complexities of the question, many influencers and even some experts have reduced this question to a simplicity that is inaccurate and misleading. They say, "It does not matter what's in your sunscreen in terms of active ingredients. Concentration does not matter. It's all about the formula."
There are always formulation considerations that can impact the efficacy and efficiency of the UV filter used in your sunscreen. The efficiency of your UV filter, i.e. how much UV light is attenuated for every 1% concentration, is definitely impacted by final formulation considerations. For example, considerations like the formulation system used, the impact of photo-stability of certain ingredients can improve or reduce the efficiency of your UV filter. (Hanay/Osterwalder, Challenges in Formulation).
However, this does not mean that sunscreen formulation exists in a void of everything we know about basic chemistry. There are well-established theoretical limits that all UV Filters and their UV efficiency operate within.
Logically, it only makes sense that sunscreens are bound by the same laws of chemistry as any other product on Earth. Drugs like Tylenol or Aspirin are dosed with active ingredients according to a margin of safety and efficacy, i.e. a 5 mg dose of acetaminophen is not the same as 500 mg. Sunscreens formulas are no different and as our case study will show, mineral sunscreens are no exception.
Let’s just say- the benefit is in the dose.
UV Filter concentration in your sunscreen does matter.
Labelled SPF and consumer perception of a sunscreen's efficacy
Most consumers still judge the efficacy of a sunscreen by its labelled SPF. It's one of the few pieces of information available to consumers that is clear and concise and consumers use it accordingly.
There are well-established limitations to exclusively focusing on a sunscreen's SPF:
SPF is derived using an in-vivo (on human) test that has been shown to be highly inaccurate. Interlaboratory variability has been shown to be anywhere from 30-50% for any tested SPF (Miksa, Lutz et al, Sunscreen Sun Protection Factor claim based on in vivo interlaboratory variability). This means that one lab could test a formula as an SPF 30 and another could test the same formula as an SPF 45.
SPF does not measure protection against long wave UVA. UVA light accounts for about 95% of the UV light that hits Earth and yet the test that measures SPF eliminates most of UVA from the solar simulating device. SPF relates mostly against a sunscreens ability to protect against sunburn and some forms of skin cancer but not against UVA light that causes pigmentation, signs of skin aging and common forms of skin cancer. In North America especially due to weaker UVA related regulations, a sunscreen can have a high SPF but relatively weak UVA protection (.
With consumers's focus on SPF, many sunscreen formulators also focus on maximizing the labeled SPF of their formula. It can very challenging to do this while balancing considerations of cost, formula aesthetics and stability. Formulators have to weigh the options of using different UV filters to cover different parts of the UV spectrum (UVB, UVAII and UVAI) and how much of each filter to use.
Why a sunscreen is more than just its SPF.
UV Filter Efficiency: industry benchmarks
Contrary to the idea that UV filter concentration does not matter, there are established industry benchmarks for estimating the amount of protection a UV filter can provide. It is also fairly well understood within the industry about which parts of the UV spectrum an individual UV filter can cover. For example, titanium dioxide can protect against UVB and some short wave UVA (UVAII) depending on particle size. However, there is no current evidence that shows that it can ever protect against long wave UVA (UVAI) sufficiently.
In keeping with our focus on all mineral sunscreens that exclusively contain zinc oxide, what is the efficiency of zinc oxide? i.e. how much protection can one reasonably expect for every single percentage of concentration.
How much protection does 1% Zinc Oxide give at every UV wavelength. (Hanay/Osterwalder, Challenges in Formulation)
What does this mean? It means we can begin to establish an approximate way to determine what type of protection we can expect for a sunscreen based on for every 1% of concentration.
How to roughly estimate what a sunscreens SPF should be based on the % of zinc oxide.
These are conservative estimations. You can improve the efficiency of your UV filter by optimizing your dispersion and film formation, improving photo-stability, preventing crystallization (in the case of some UV filters like avobenzone or Tinosorb S). However, this is a helpful benchmark. If your the efficiency of your UV filter is 2x, 3x, 4x or 5x better than the benchmark, it's fair to question why. Is it something really innovative or is something else happening?
What is an SPF booster?
As mentioned, most consumers judge a sunscreen by its labelled SPF. It's in the interest of a sunscreen formulator to maximize the SPF. A formulator could increase the amount of a UV filter, improve the UV filter's efficiency or use a third option: an SPF booster.
In this case, we are looking at two types of SPF boosters;
i.e. Butyloctyl Salicylate and Tridecyl Salicylate: pseudo UV filters that are listed as inactive since they are not regulated by the FDA or Health Canada as recognized active ingredients. They are modified forms of the UV filter octisalate , otherwise known as ethylhexyl salicylate. There is strong evidence to suggest that butyloctyl salicylate can attenuate UV light and have some anti-inflammatory capabilities. Ingredient supplier Sunjin Chemical has stated that butyloctyl salicylate is almost identical to octisalate and was intentionally modified in order to subvert North American regulations. It's unclear whether tridecyl salicylate actually attenuates UV light or works purely as an anti-inflammatory.
e.g. Bisabolol: naturally derived or synthetic anti-inflammatories that reduce skin redness and the creation of pigmentation. We chose bisabolol because it's specifically marketed as an SPF booster when used with argan oil and vitamin E under the trade name Sunboost ATB (sold by Kobo Products). However, it would be worth considering if other known skin redness agents like niacinamide, aloe vera, allantoin etc could have similar effects. These anti-redness ingredients can impact the biological endpoint of skin redness/darkness that is used as part of the in-vivo SPF and PA tests and potentially skew results. They do not actually attenuate UV light like a UV filter.
SPF Boosters Butyloctyl Salicylate, Tridecyl salicylate and bisabolol
Results:
We looked at a total of 69 all mineral sunscreens that contained zinc oxide as their only active ingredient. We split these into 4 groups according to their Zinc Oxide concentration and labelled SPF.
Sunscreen Groupings and Average SPF units/1% Zinc Oxide Concentration
Groups of Mineral Sunscreens by SPF, Zinc Oxide Concentration
See Appendix 1 for a full list of sunscreens included in each Group.
Breakdown of All Zinc Oxide Sunscreens by Zinc Oxide % and SPF
The majority of the all zinc oxide sunscreens that we looked at (57.9%) were made up with formulas that included relatively high concentrations of zinc oxide of over 15% and moderate SPF's of 35 or less. This group had an average of 1.53 SPF units for every 1% of zinc oxide and is very close to the previous industry benchmark that we looked at of 1.4. Groups 1 and 3 both include formulas that include relatively low concentrations of zinc oxide at less than 15% and have a range of average SPF units/1% ZnO used of 2.8-4.21 SPF units/ZnO. These are performance metrics that are markedly higher than the industry benchmark of 1.4.
Group 1: ZnO < 15% AND <SPF 35
Group 1: Low Zinc Oxide Concentration with SPFs lower than 35, 64% contained SPF boosters
Group 2: ZnO 15%+ AND SPF 35 +
Group 3: ZnO <15% and SPF 36+
Group 4: ZnO 15%+ and SPF 36+
Key Take-Aways:
No Magic Zinc
Group 1 and Group 3 had remarkably different results than Group 2 and Group 4. Group 1 had relatively low zinc oxide concentrations, typically in the 10-12% range of zinc oxide concentration and yet most of them obtained SPF’s of 30. This means that for every 1% of zinc oxide used, they could get an SPF performance of 2.8 units. This is double what we might conservatively expect from traditional SPF performance for zinc oxide.
Group 3 is the biggest standout though. With its lower concentration of Zinc Oxide but high SPF, 81% of the sunscreen formulas in this group contained either of the salicylates or bisabolol. They had an average 4.21 SPF points for every 1% Zinc Oxide, a 300% increase over the theoretical average.
That means for formulas that might have 12% zinc oxide and you would conservatively expect a SPF of 16.8, they instead had SPF’s of 50.
You can compare this to Group 2, the group that had high concentrations of zinc oxide with moderate SPF’s of 35 or lower. Within this group, only 18% of formulas had any or all of the three ingredients we studied. They had an average 1.54 SPF points for every 1% of Zinc Oxide. That means that for every formula where you might expect a 22% zinc oxide formula to have an SPF of 30.8, they had a labelled SPF of 30.
There is a clear correlation between these low zinc oxide sunscreens with high SPF’s using one or more of these three ingredients. It’s not a huge logical leap to say that these ingredients that are marketed as SPF boosters, are indeed SPF boosters. They are being used intentionally to boost the labelled SPF and reduce the amount of zinc oxide in the formula, most likely due to cost considerations, formulation challenges and aesthetic implications.
How does this impact the consumer? Is it really 'all-mineral'?
In the interest of transparency for consumers, brands cannot claim that any formula that contains either butyloctyl salicylate and/or tridecyl salicylate is ‘all-mineral’. Sunjin Chemical is the first raw material supplier to openly admit they modified ethylhexyl salicylate (i.e. the organic ‘chemical’ UV filter octisalate) to get the resulting butyloctyl salicylate. They made minor changes to the portion of the molecule that is not responsible for UV attenuation. This is part of an industry trend to alter chemicals so that they do not appear as regulated active ingredients and can instead appear in the section for inactive ingredients.
We foresee this becoming a major source of consumer discontent and potentially even litigation. Consumers are expecting that their ‘all-mineral’ formulas will be free of ‘chemical’ UV filters and we expect major pushback for any formula that misrepresents themselves.
Impact on UVA
The potential impact on the UVA is our main concern when formulas reduce the concenration of zinc oxide and replace it with an SPF booster. In North America, the two current UV filters that provide UVA protection are zinc oxide and avobenzone. When you lower the concentration of zinc oxide but maintain the SPF with SPF boosters, the level of protection against UVA can only be diminished. This means that these formulas are leaving consumers with reduced protection against the UV wavelengths responsible for many forms of skin cancer, photo-aging and pigmentation.
It is important to note that while the UVA protection of these types of formulas will be reduced, the labelled PA rating may not. The PA rating is a measurement of UVA protection that is derived from the in-vivo Persistent Pigment Darkening test. Several of the formulas within Group 3 that have low zinc oxide concentrations and high SPF’s, also have high PA ratings of ++++. Sunjin Chemical mentions in their own testing that butyoctyl salicylate increased their PA rating by about 15% versus the control. While it may be possible that butyoctyl salicylate could be improving the UVA protection of a formula by optimizing zinc oxides performance as a dispersion enhancer. It seems more likely that the in-vivo PPD test is being influenced by the anti-inflammatory component of butyloctyl salicylates and that it’s reducing the biological endpoint of the test but not improving actual UV attenuation in the UVA portion of light.
Final Conclusions:
Brands and formulators have taken advantage of consumer confusion in thinking that the concentration of their zinc oxide does not matter. If a formula with 5% zinc oxide can get an SPF 50 then what is the difference and/or benefit in a formula with 25% zinc oxide? While our data set of all zinc oxide based sunscreens was relatively small, there is a clear trend of formulas with relatively low concentrations of zinc oxide getting disproportionately high SPF’s. The fact that 81% of Group 3 formulas with low zinc oxide concentrations and high SPF’s use either a salicylate and/or bisbolol compared to Group 2 with high zinc oxide concentrations and lower SPF’s of 35+, only 18% used either a salicylate or bisabolol type ingredient. Clearly, the salicylate ingredients and bisabolol that are marketed as SPF boosters are performing as SPF boosters. However, there is two fold cost to the consumer in the form of misbranding these sunscreens as ‘all-mineral’ and to the potential UVA protection if the overall concentration of zinc oxide is reduced.
At the time of writing, brands are starting to change the way they label their sunscreens containing butyloctyl salicylate and tridecyl salicylate in their inactive ingredients. We have seen at least one brand start to label their sunscreens as containing ‘all-mineral actives’ instead of as being ‘all-mineral’. You could consider this a step towards greater transparency for the consumer. However, it’s also an admission that butyloctyl salicylate and tridecyl salicylate are close enough to ethylhexcyl salicylate (octisalate) that it’s a potential liability issue and one of misbranding to label them as the latter.
There is no doubt that the North American sunscreen industry is going to have to deal with the pervasive use of salicylates and SPF boosters at some point. Consumers, especially within the ‘clean beauty’ category, are highly educated and ingredient conscious. To these conscious consumers, it’s an even bigger issue to sneak an ingredient in the inactives like the salicylate that they were actively trying to avoid.
Our wish as a company that has been developing mineral sunscreens for the past 15 years is that consumers begin to understand overall that the concentration of their active ingredient matters. Sunscreens are one of the most important health decisions that a consumer can make and understanding the essential fact that the dose makes the benefit and concentration matters is crucial.
Ava Isa Line of Mineral Suncare with 25% Zinc Oxide and no ‘chemical’ SF
We created our Ava Isa line of mineral sunscreens to contain the maximum 25% of zinc oxide with no ‘chemical’ SPF boosters like butyloctyl salicylates or tridecyl salicylates. We do not use anti-redness/erythema SPF boosters like bisabolol or any similar type ingredient. We offer real protection with high UVA protection for your best daily mineral option.
As a thank you for reading to the end, use promo code TRUEZINC for 15% off all Ava Isa products.
Don’t forget to subscribe to our Newsletter here for more skincare education, tips & tricks.
You’ll be the first to know when new products launch or when promotions begin, and will receive an exclusive 10% discount to our online store for your first purchase just for signing up.
For more skincare education, tips & tricks follow us on Instagram and Tik Tok @thesunscreencompany