A Deep Dive into Understanding SPF Boosters and Sunscreen Doping

Taking at closer look at chemical SPF boosters butyoctyl salicylate, tridecyl salicylate, polyester-8, ethylhexyl methoxycrylene, and ethyl ferulate

We are going to be looking at a specific type of SPF boosters that are becoming much more common in both mineral and ‘chemical’ sunscreens. These are a class of SPF boosters that are modified versions of ‘chemical’ UV filters like octisalate, octocrylene, and octinoxate. They were intentionally modified by raw material suppliers so that sunscreen formulators could add them to the inactive portion of a sunscreen, out-of-sight from the active ingredient section. We take issue with their use when they are used to reduce the concentration of the active UV filters, especially zinc oxide in mineral sunscreens, as we fear this can negatively impact the overall UVA performance of the sunscreen. However, we also object to their use when it leads to deceptive marketing like calling sunscreens ‘all-mineral’ or O-free (i.e. octinoxate or octocrylene free). The fact is that consumers are savvy and ingredient conscious and hiding these chemical analogs in the inactives is misleading especially when certain marketing claims are made.

We will be looking at five common chemical analog SPF boosters: butyloctyl salicylate, tridecyl salicylate, polyester-8, ethylhexyl methoxycrylene, and ethyl ferulate. We’ll be taking a deep dive into how they compare with the original chemical UV filter, the degree to which they were modified, derivation, whether they attenuate UV light and which part of the UV spectrum, molecular weight and share an overall assessment of safety and efficacy.

Butyoctyl salicylate and tridecyl salicylate

Butyloctyl salicylate and tridecyl salicylate are modified versions of the soluble organic ‘chemical’ UV filter octisalate, otherwise known as ethylhexyl salicylate. These are perhaps the most common SPF booster used pervasively in both ‘all-mineral’ sunscreens and ‘chemical’ UV sunscreens. We’ve shared our concerns previously when these ingredients are used to lower the concentration of zinc oxide in mineral sunscreens and when they are used in combination by pregnant women and kids. Both ingredients have the same derivation as octisalate and are petroleum derived. They also have molecular weights well below 500 Daltons, and they are confirmed to penetrate the skin into blood and tissue. Octisalate has been confirmed to likely penetrate across the placenta, it’s reasonable to assume that butyoctyl salicylate and tridecyl salicylate would as well. While octisalate is regulated in the US and Canada and cannot be used at concentrations higher than 10%, there are no upper limit concentrations for use for butyoctyl salicylate and tridecyl salicylate. The maximum recommended use levels by raw material suppliers are 10% and 6% for butyoctyl salicylate and tridecyl salicylate respectively. Conversely, the Therapeutic Goods Administration of Australia does limit butyloctyl salicylate to 1% and does not recommend that children under 4 or pregnant women in their last trimester use it.

These ingredients are marketed as both anti-inflammatories and pigment dispersants. They were originally thought to improve the performance of sunscreens by improving the dispersions of the mineral particles. However, we now know that butyoctyl salicylate does also attenuate UV light (mainly in the UVB range). It’s not clear whether tridecyl saclicylate also attenuates UV light, it’s quite possible since the part of the molecule that attenuates UV light is the same amongst all three ingredients. It’s quite likely that all three ingredients also boost the SPF of a formula by working as an anti-redness ingredient. This means that it might game the SPF test that uses redness as a bio-marker to give a higher SPF determination and tamp down the persistent pigment bio-marker that is used in the PA rating for UVA protection.

Summary: How different are butyoctyl salicylate and tridecyl salicylate from octisalate?

We would rate butyoctyl salicylate and tridecyl salicylate as being very similar to the chemical UV filter octisalate. They are the similar molecular weights and permeate the skin, butyoctyl salicylate at the very least attenuates UVB light like octisalate, their salicylate portion of their molecule means they have similar safety issues for pregnant women and young children (especially when used in combination). They do seem as though they were created intentionally to mimic the effects of octisalate while not having to be declared as an active. We do not advocate for their use to lower the concentration of zinc oxide or titanium dioxide in a mineral formula.

Polyester-8 and Ethylhexyl Methoxycrylene

Polyester-8, known as the brand name Polycrylene, and ethylhexyl methoxycrylene, sold under the brand name Solastay, are marketed as alternatives to the UV filter octocrylene, or at least some of its functions. Both are marketed for their ability to enhance the photo stability of other UV filters, something that octocrylene is also known for. Octocrylene rose to prominence largely in part due to its ability to stabilize the otherwise unstable UV filter Avobenzone. It’s been estimated that 36% of avobenzone without the photo-stabilization of octocrylene is lost within within 15 minutes of sun exposure. Ethylhexyl methoxycrylene is marketed as a way to formulate ‘O-free’ (octocrylene, octinoxate, oxybenzone) sunscreens and provides similar photostabilization of UV filters and anti-oxidants like resveratrol. Polyester-8 is also marketed as a photo stabilizer but is confirmed to also actually attenuate UVB light (peaking at 303 nm), approximately 1/3 of an equivalent amount of octocrylene. At its recommended use level of up to 4%, it’s not likely a meaningful way to boost the SPF of a sunscreen according to the manufacturer.

Polyester-8 is substantially different from octocrylene in terms of molecular weight. At 1900 Daltons, compared to octocrylene’s 361 g/mol, is much larger and therefore not likely to permeate through skin. Ethylexyl methoxycrylene is very similar in size at 391 g/mol. Octocrylene has been shown to potentially degrade into benzophenone over time in finished sunscreen formulas, and does not readily biodegrade. It would be prudent to ensure that polyester-8 and ethylhexyl methoxycrylene do not have similar degradation issues and potential to accumulate in the environment. In 2021, the chemical company BASF actually announced that they were discontinuing the sale of octocrylene because of ‘growing concerns’. Part of the issue remains that the public has never had full transparency into what these ‘concerns’ were and there it’s hard not to be suspicious of what these issues are. It therefore remains challenging to know to what extent these octocrylene alternatives really improved these issues.

Summary: how different are polyester-8 and ethylhexyl methoxycrylene from octocrylene?

Polyester-8 is substantially different from octocrylene by virtue of being dramatically larger in size. It’s not clear if octocrylene degradation would be a potential issue though. It’s unclear how different ethylhexyl methoxycrylene is from octocrylene as it's a patented ingredient and information is currently limited to what the manufacturer is willing to disclose. As more independent research is done then it will become clearer how meaningful the differences are- its small molecular size does mean that it’s likely to permeate into skin and this is a red flag.

Ethyl Ferulate

Ethyl Ferulate is part of the same cinnamate family as octocrylene and octinoxate. It is currently marketed as a booster, however, its attenuation is more in the short wave UVA (UVAII) portion of light. Unlike the previous ingredients, Ethyl Ferulate has a completely different derivation than octinoxate and octocrylene. It is derived from Ferulic Acid and is not a petroleum by-product. It attenuates UV light by having a similar chemical structure to other UV filters. It is marketed as requiring 1/10 the amount of octinoxate to deliver similar performance.

However, it was not created intentionally by modifying one of the existing chemical UV filters. It is something found in nature that was discovered to have attenuating properties in addition to its anti-oxidant properties. At 222 g/mol, it is quite small in size and likely to permeate through skin. The only theoretical concern would be potential permeation and by virtue of isomer function (lock and key for hormones and hormone receptors), something with a similar shape could weakly bind with a hormone receptor. No evidence exists that this occurs to date.

Summary: how different is Ethyl Ferulate from octinoxate?

Ethyl Ferulate is substantially different than octinoxate or other UV filters from the cinnamate family. It has plant-based derivation, and is not merely a modified version of octinoxate.

nscreen performance, but be wary of products that might rely on sunscreen doping. Understanding the ingredients and how they work will help you make informed choices, ensuring that you get the protection you need to enjoy the sun safely.

Conclusion: Are all SPF boosters bad?

The intent to improve a sunscreens importance is not inherently bad. SPF boosters in themselves are not inherently bad. However, we do take issue with the idea that as consumers become more sensitive to certain ingredients appearing in the Active Ingredient section, raw material suppliers create modified versions that can sneak into the inactive section. We also take issue when brands use misleading marketing to then promote their formulas as ‘all-mineral’ when they are not, or claim their formulas are “Octocrylene-free” but are not truly. We also do not believe these ingredients should ever be used to replace the UV filters providing long wave UVA. It’s true that many consumers rely solely on the labelled SPF to judge a sunscreen. However, as brands, we have to hold ourselves to a higher standard and not skimp on performance in the very critical portion of long wave UVA. We have to stop trying to provide the bare minimum and look to maximize performance for the safety and look of our customers skin.

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