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Sunscreen and UV filter myth busters - nanoparticles

There are so many myths surrounding sunscreens and UV filters, it can be hard to separate fact from fiction. And while the majority of myths are spread by social media, we are also seeing some common misconceptions spread within our industry.   
 
I have gathered together the other solar experts here at Croda to debunk some of the biggest sunscreen and UV filters myths.  

In this first blog we are focussing on nanoparticles, and the myth relating to particle science and nanoparticles.
Mythbusting with Croda

Meet the Myth Busters team:

Dr Rob Sayer, is our Research & Technology Manager with over 13 years’ experience with Croda’s metal oxides. With a background in academia and physical chemistry he has authored numerous academic papers and presented at numerous conferences on the topic of metal oxide innovation. 

Clare Liptrot, our Global Regulatory Manager, has almost 20 years’ experience in consumer product safety. She is a member of EFfCI and sits on several working groups, and is the current chair of the Regulatory Affairs & Product Safety Group and Polymer WG.

Joseph Peake, Research Team Leader Sun Care Synthesis, has over 8 years at Croda working on innovation of metal oxide UV filters and a further 2 years working on titanium dioxide for dye sensitised solar cells. 

Mythbusters team

Lastly, I am the Marketing Manager for Solar protection. I have over 20 years’ experience in formulation, claim substantiation, innovation management and marketing, primarily in solar protection.  I have a first class MChem from University College London and a Diploma in Cosmetic Science.

In this first blog we have tackled the main myths around “nano” and particle technology. For each myth we have referenced the key citations where you can find the evidence for our conclusions. The full list of citations can be found in the presentation. 

Nano UV filters are small
This is a big myth, pardon the pun. In the world of UV filters, nano TiO2 and ZnO are BIG UV filters. Most chemical/organic sunscreens have a typical molecular weight of less than 300 Daltons which would correlate to a size of less than 1 nm. So, it is these types that are small. Mineral/inorganic UV filters are much larger than this, even “nano” TiO2 and ZnO are typically around 30nm, so are 30 times the size.

Nano TiO2/ZnO penetrates the skin
This myth ties in to the first one, people assume as “nano” is small it will penetrate the skin and they are unaware of the extensive safety data that exists. Evidence shows that “nano” and “non-nano” TiO2 and ZnO shows they largely do not penetrate the skin.
This is confirmed by the EU Scientific Committee on Consumer Safety and the US Food & Drug Administration.ii 

Nano means 1-100 nm in size
This is part myth part reality. It does generally mean this BUT there isn’t a single global definition of nano. Particles exist in a continuum of sizes, and have various structures, internal and external dimensions, which is why the definition is so complex.
Even in Europe where “nano” is most well defined, there is no consistency between cosmetics and chemical legislation. Also now we are seeing divergence even in member states, for example France.
There is also no standard regulated test method, and different test methods give different results, which compounds the problem.
At Croda we can help you navigate the definitions and measurement of nano TiO2 and ZnO to allow you to determine what you need for the regulatory obligations in the markets you are selling to.

Nano TiO2 is carcinogenic
The controversy around TiO2 is linked to the fact that in Europe only it is classified as a category 2 carcinogen by inhalation when the particles are a certain aerodynamic diameter. This is because it is a fine particle that could be inhaled. Croda’s Solaveil TiO2 range however are not classified as carcinogenic.
The vast majority of sunscreen are applied dermally, and in Europe TiO2 is not allowed in formats where they could be inhaled anyway.
TiO2 applied to the skin in lotions and creams is not carcinogenic, it largely does not penetrate the skin, and is safe and effective. 

Mineral/inorganic UV filters will be banned as they are microplastics
This myth comes from a misunderstanding of the composition of mineral UV filters, which in the main do not contain polymeric materials. 
Microplastics are particles containing a solid polymer to which additives or other substances have been added, and where ≥1% w/w of particles have (i) all dimensions 0.1µm ≤ x ≤ 5mm, or (ii), for fibres, a length of 0.3µm ≤ x ≤ 15mm and a length to diameter ratio of >3. 
None of the ingredients we use in our Croda Solaveil UV filters are polymeric, so they are not classified as microplastics.

If I use a nano UV filter I have to register my finished product
This can be very confusing, so it is no wonder it is a common myth. The Cosmetic Product Notification Portal (CPNP) states that products containing nanomaterials must be specifically notified under six months prior to placing on the market, unless the nanomaterial is a UV filter, colorant or preservative (in this case it must be listed in the respective positive list in its nano form), or is listed in Annex III in its nano form. All our “nano” products are listed in the positive list in their nano form, so you do not need to notify them in the CPNP.

Mineral/inorganic UV filters are whitening
This myth has been around for a number of years and often discourages people from trying sunscreens containing TiO2 and ZnO. Mineral/inorganics work by both absorbing and scattering/reflecting light. 
If they scatter visible light back to the surface then they can leave a white cast on the skin, but Croda is continually developing technology to avoid this phenomenon.
One example of this is Solaveil MicNo. Find out more here.

High SPF mineral-only formulation is not possible as formulations feel too draggy
Whilst formulating mineral-only high SPF can be more challenging, it is indeed possible to achieve formulations with highly spreadability and non-greasy sensorial. This video shows the application of an SPF 40 mineral only sunscreen containing Solaveil MicNo and Solaveil Harmony.

Mineral sunscreens can be unstable
The truth is that ALL types of sunscreens can be unstable, and all types of UV filters pose challenges for formulators.
There are some myths that organic/chemical filters are “easier” to stabilise in solution, compared to particles which are harder to stabilise (as they tend to agglomerate and sediment).
However organic/chemical filters can crystalise out of solution and require the right oil at the right level to be stable, so are not necessarily the “easier” option.
Inorganic/mineral filters are available in coated and dispersed forms which are highly stable to agglomeration and sedimentation, which makes formulation and stabilisation more straightforward.

Sun protection formulations can cause allergic reactions and are not suitable for sensitive skin
Reactions to sunscreens are rare and can be a result of a sensitive or allergy to any of the ingredients. An allergy to UV filters is even rarer, but it can occur in some individuals. 
Benzophenone, cinnamates and dibenzoylmethanes are known to induce photo-allergic reactions or photo-contact dermatitis. This occurs when the sunscreen product, in combination with exposure to UV rays, causes an individual to develop a reaction. 
Zinc Oxide and Titanium Dioxide have not been reported to cause contact allergy so are an excellent choice for people who have experienced sunscreen photo-allergy.iii

In our next blog we will be tackling the topic of “clean” sunscreens and environmental impact. If you think of any myths that you would like us to cover, please contact us.

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i https://pubmed.ncbi.nlm.nih.gov/20354643/
ii https://www.federalregister.gov/documents/2019/02/26/2019-03019/sunscreen-drug-products-for-over-the-counter-human-use 
iii https://acaai.org/resources/connect/ask-allergist/red-itchy-bumps-wearing-sunscreen-outside

Mythbusting with Croda - Issue #1

Mythbusting with Croda
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Solaveil™ Mythbusters - Particle Science

Mythbusting with Croda
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