Podcast: Episode 29, the composition of sunscreen products

Listen to the audio episode to understand the composition of your sunscreen

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THE COMPOSITION OF SUN PRODUCTS

Creams, oils, sprays, sticks, ... sunscreens have very different textures with, however, one thing in common: ultraviolet filters. What are UV filters? How do they work? Are some better than others?

WHAT ARE UV FILTERS?

There are different types of sunscreens, they are classified into two categories:

• organic filters , also called "synthetic" or "chemical"
• mineral filters , also called "inorganic" or "physical"

⚠️ Warning: The term "chemical filter" is confusing because chemistry is the study of matter. Thus everything that touches can be studied under the prism of chemistry. We can say that we drink water or we can say that we drink H2O in reference to the water molecule which is composed of two hydrogen atoms and one oxygen atom.

⚠️ Warning #2: The term "organic filter" is a false friend with English. "Organic" refers to molecules that contain carbon and hydrogen atoms. It's "organi que " like organic chemistry and not "organi c " like the English translation of biological.

WHAT ARE ORGANIC FILTERS?

Organic filters are filters that have been synthesized for this purpose, they are manufactured using chemical processes that are not authorized in the COSMOS standard . So if you are looking for a certified organic sunscreen, it will not contain an organic filter. They are mostly soluble in the fatty phase and therefore the formulas contain a significant fatty phase. However, there is a very small minority of filters that are soluble in the aqueous phase, such as DPDT.

Their advantages:

✅ they protect very well and achieve high SPF

✅ pleasant texture , without white trace.

Their disadvantages:

❌ some are a little less well tolerated such as avobenzone, octocrylene, and oxybenzone. But if you don't know, it's because you certainly haven't experienced any inconveniences and therefore don't need to banish them for this reason.

❌ some are less stable , such as avobenzone. They become less effective over time or in the presence of other raw materials. But this is a problem that concerns formulators more than consumers.

❌ not accepted in organic cosmetics

🔎 INCI names:

• Butyl methoxydibenzoylmethane (commonly called avobenzone)
• Ethylhexyl triazone
• Benzophenone-3 (commonly called oxybenzone)
• Ethylhexyl methoxycinnamate (commonly called octinoxate)
• Octocrylene
• Ethylhexyl salicylate
• Homomentyl salicylate
• Bis-ethylhexyloxyphenol methoxyphenyl triazine
• Drometrizole trisiloxane
• ...

WHAT ARE MINERAL FILTERS?

Mineral filters are obtained from minerals and are accepted in certified organic formulas . However, the dispersion of these inorganic particles is not always easy for formulators.

To facilitate the dispersion of mineral filters, manufacturers create coatings which can also improve their sensorialities. However, these coatings are not always accepted by the COSMOS standard for organic cosmetics.

The size of the mineral filters also greatly impacts their sensorialities. The smaller the filter particles, the less white marks they leave on the skin. The white finish of certain mineral sunscreens is particularly deprecated, because it is particularly restrictive on dark skin.

The use of nanoscopic filters , with particles less than 100 nanometers or 10,000 times smaller than one mm, considerably reduces the white finish on the skin.

The SCCS, the Scientific Committee on Consumer Safety (whose acronym is SCCS) declared nanoparticles as safe and do not penetrate the skin ¹ in view of the scientific studies available in 2014 when they studied this question. If an ingredient of your cosmetic is of nanoscopic size, the mention nano between square brackets will be present in the list inci Example: titanium dioxide [nano] .

Their advantages:

✅ accepted in organic cosmetics

✅ very well tolerated

✅ stable

Their disadvantages:

❌ leave white marks

❌ textures that are a little heavier / plastery

❌ dispersion more difficult for formulators

🔎 INCI names:

• titanium dioxide (TiO2)*
• zinc oxide (ZnO)

* the safety of titanium dioxide is being reassessed in certain cosmetics. Indeed, the European Food Safety Authority (EFSA) recently changed its opinion ² on titanium dioxide, and no longer considers it safe as a food additive. In June 2022, the European Commission requested its reassessment in certain cosmetics, it should be available around March / April 2023.

HOW DO UV FILTERS WORK?

Both organic sunscreens and mineral filters absorb UV rays and transform them into imperceptible heat . And this is how they protect our skin from the sun's rays.

⚠️ Attention, recent studies³ question what we hear a lot in the cosmetics industry, concerning the functioning of mineral UV filters. They only reflect light, like mirrors on the surface of the skin, up to 5% of their sun protection. 95% of the sun protection provided by mineral filters would be thanks to a process of absorption of UV rays, like organic filters.

WHY DON'T ALL SUN PRODUCTS TICK ALL THE BOXES?

Sunscreens are one of the most technical categories of cosmetics formulation.

The solubilization or dispersion of the filters must be perfect to have an even layer on the skin on application.

The regulatory landscape is also very complex with different legislation between countries. Some countries consider sunscreens as " OTC" for "over the counter" or " QD " for "quasi drug", categories between cosmetics and drugs, with separate regulations. Thus, it is very difficult to formulate a sunscreen with a very high SPF that is approved worldwide.

Patents are additional challenges of SPF formulation because many large groups have patented combinations of filters thus reducing the possibilities for other companies.

From an organizational point of view, it is more difficult to be reactive when formulating sunscreen because the SPF and UVA tests are added during development and they are more difficult to predict. If the desired SPF is not directly achieved on the formula under development, it is then necessary to reformulate, and re-submit to the SPF / UVA test . These tests are expensive and time- consuming .

For formulators, consider using the BASF simulator before formulation for a rough approximation of the SPF.

CAN I MAKE MY SUNSCREEN AT HOME?

I never recommend homemade recipes or other DIY, Do It Yourself , for cosmetics because there is no quality control, nor any verification as to safety. But for sunscreens, I implore you, don't do DIY to achieve sun protection .

The formulation of sunscreen is already complicated for manufacturers who have great agitators, in particular for the solubilization and or the dispersion of filters so the chances that at home you will manage to see a formula which is applied in a homogeneous layer is really slim . Moreover, the SPF is not only achieved thanks to sunscreens, there are many other factors that affect the SPF, in addition to sunscreens:

• the other ingredients in the formulas because there are raw materials called boosters, which help to achieve the desired SPF
• the distribution of sunscreens within the formula
• the interaction of the ingredients in the formula because we saw that some filters were not very stable
• the pH can vary the SPF obtained (example: zinc oxide).
• the spreading properties of the formula on the skin, the texture of the sunscreen must allow application in a homogeneous layer, that is to say of the same thickness and concentration of active ingredients everywhere on the skin.

All these criteria cannot be optimally managed at home.

Ratings

¹Scientific Committee on Consumer Safety. Guidance on the Safety Assessment of nanomaterials in cosmetics . 2012. Available at: https://ec.europa.eu/health/scientific_committees/consumer_safety/docs/sccs_s_005.pdf

²EFSA. Titanium Dioxide: E171 is no longer considered safe as a food additive. 2021 . Available at: https://www.efsa.europa.eu/en/news/titanium-dioxide-e171-no-longer-considered-safe-when-used-food-additive

³ COLE C, et al. Metal oxide sunscreens protect skin by absorption, not by reflection or scattering . 2015. Available at: https://onlinelibrary.wiley.com/doi/full/10.1111/phpp.12214