Science made easy: the anti-pollution skincare (I)

About a week ago I shared this interesting article in social media and some of my readers complained that it was too scientific (and too long for smartphone generation) for them and asked me to explain the "stuff" in an easy language. I'll try my best and in order not to bore the modern, smartphone generation reader, I'll break the "stuff" into several posts. In this post, I'm going to talk a little bit about the anti-pollution market, the air pollution and its effect on our largest organ, the skin.

The anti-pollution market is one of the fastest growing branches of the global personal care market. Alone in the UK, the overall retail market had a 30% growth in the first six months of 2017 (anti pollution facial masks enjoyed a 112% growth according to NPD Group).

The trend has started in Asia (still the biggest global market with the latest innovations) where we have some of the most polluted mega cities of the world and then expanded to other parts of the world.

In order to have a share of this market, create effective products and be able to explain the philosophy of the products to our customers, we first need to understand the impact of the pollution on the skin and that is exactly what I'm trying to explain in a (hopefully) short blog post.

What is air pollution?

If you have had the pleasure (or the misery) of spending a few hours on the busy streets of a mega city, you are certainly familiar with the superficial meaning of pollution and its impact on the skin:

the unpleasant greasiness and stickiness you feel over your skin and the shock you have in the evening after you apply the white cotton pad soaked in your cleansing milk or micellar water over your face.

This is just the tip of the iceberg and the very (literally) superficial impact of pollution over the skin. Unfortunately, the damage doesn't end here and the impact of pollution penetrates much deeper to the skin and doesn't remain only on top of the stratum corneum.

Air pollution in urban areas (human caused air pollution) is mainly cause by combustion of fossil fuels (cars, heating, industrial processes, air craft etc.) and is composed of different compounds. Depending on the composition, air pollutants have different targets and pathways in damaging the skin (apart from the obvious harm which is the sticky layer you feel over your skin after being in a polluted area)

Primary pollutants:

These are compounds that are directly emitted by the pollution source and include:

• gases such as SO₂, NOx
• Heavy metals (lead, mercury)
• low molecular weight hydrocarbons
• particulate matter (PM)
• Persistent organic pollutants (these are compounds such as dioxins (not to be mistaken with dioxane which is a byproduct of ethoxylation) that do not biodegrade and hence accumulate adding to the danger). They are formed when chlorine containing material is burned

Secondary pollutants:

These are compounds that are not directly emitted from the pollution source but are formed in the air through chemical reactions of the primary pollutants and include:

• ozone (O₃)
• NO₂
• peroxy acetyl nitrate
• hydrogen peroxide
• aldehydes

PM (particulate matter) which is probably (in our case) the main concern consists of particles of different sizes and compositions. They are classified into different size classes. Depending on their size (and active surface) they can absorb and carry various pollutants such as various gases, organic compounds, polyaromatic hydrocarbons (PAH), heavy metals etc

PMs are mainly classified into:

• PM_2.5–10 (coarse particles, 2.5–10 μm)
• PM_2.5 (fine particles, <2.5 μm)
• PM₁₀ (<10 μm),
• ultrafine particles (UFP, <100 nm) 

(imagine PMs like a rolling sponge that absorbs and carries dirt. Depending on the size of the holes on the sponge, it can carry various particles with itself)

What does this mean for our skin?

The skin as our largest organ and a real boundary between our body and the environment, is the most widely affected and exposed organ when it comes to air pollution. The damage penetrates lower than the stratum corneum (the uppermost layer of our skin).

Most studies carries on consider the impact of PM and ozone of the skin and unfortunately, some of these studies are carried on animals. Although we do not advocate animal testing, we're mentioning the test results here.

PM consists of a carbon (charcoal) core of various diameters that can absorb and carry other pollutants such as:

• heavy metals
• Polycyclic aromatic hydrocarbons (PAH)
• Nitrates (NOx)
• Sulfates (SOx)

Apart from sticking to the skin and forming that unpleasant greasy and sticky film over the skin, they produce Reactive Oxygen Species (ROS) and induce an oxidative stress in the skin (in a very simplistic manner, compare this to the free radicals that promote the oxidation of your precious unsaturated plant oils).

These nasty ROS further trigger the secretion of pro-inflammatory proteins (as a defensive response from the skin) and matrix metalloproteins that consequently degrade the skin collagen and cause premature aging.

Are you still with me? I spare you the different mechanisms of the ROS but if you are interested and have the stomach to read and digest the whole material, I really recommend you to read the original article.

PAHs (Polyaromatic hydrocarbons) that adhere to fine and ultrafine PM are lipophilic molecules that can penetrate through skin barrier (they disrupt stratum corneum and tight junctions) and directly affect skin cells such as melanocytes and keratinocytes.

Ozone (O₃) which is a highly reactive molecule and a major pollutant is formed by the photochemical interaction between UV radiation, hydrocarbons, nitrogen oxides and volatile organic compuonds (VOCs). (This is exactly the same Ozone which is created by UV disinfecting lamps. Like many other evils, it can be quite useful when you can master it but turns into evil when you lose control over it).

Due to its high reactivity, it is believed that ozone's harm is confined to the stratum corneum and it can not penetrate lower layers of the skin. Its main role is to deplete the stratum corneum and skin barrier from the inherent anti-oxidants (such as skin's own vit E) and promoting a lipid peroxidation of skin barrier lipids and hence compromising the skin barrier and inducing pro-inflammatory reactions. Obviously, UV exposure enhances the damage of the ozone.

One of the measurable effects of oxidative stress is the peroxidation of skin's own squalene.

Squalene should not be mistaken with squalane. Squalene is a triterpenoid produced by plant and animal cells (as well as human body). It was originally separated from shark liver (which is still one of the main sources of squalene and squalane). It is available in plant oils such as wheat germ oil, rice bran oil, amaranth seed or olive oil and it could be prepared synthetically or by fermentation from yeast.

Squalene is the precursor of sterols (both animal and phyto sterols), another precious group of unsaponifiables in plant oils and cosmeceuticals. It is skin’s most important protective lipid. Because it is highly unsaturated and prone to oxidation, we use its sister "squalane" in cosmetic industry.

Squalane is produced (it doesn't exist naturally) by hydrogenation (saturation) of squalene and has a much longer shelf-life and much higher resistance against oxidation.

Squalene is highly unsaturated and prone to oxidation. It is secreted by our sebaceous glands (about 12% of sebum consists of squalene) and should be considered as one of skin's own antioxidants.

Research shows that squalene is one of the main targets of oxidative stress triggered by air pollution. Not the squalene, but its peroxidation byproducts, trigger inflammatory reactions in skin and cause wrinkle formation, acne and camedogenesis.

Bottom line:

The impact of pollution goes much deeper than stratum corneum and the sticky skin feel we have after being on a busy street for a few hours.

Different air pollutants react with skin via different pathways but basically they can damage the barrier function, penetrate into lower layers of the skin and trigger some immuno-responsive inflammatory reactions. The most significant effects include:

• reduced moisture (or increased TEWL)
• Increased pigmentation
• acne formation
• collagen damage
• reduction of skin's own anti-oxidants
• wrinkle formation and premature aging
• increased sensibility to UV light

If you can bare with me, we'll continue this topic in another post. Stay tuned for the next part.

Further reading:

• Juliano, Claudia, and Giovanni Antonio Magrini. "Cosmetic Functional Ingredients from Botanical Sources for Anti-Pollution Skincare Products." Cosmetics 5.1 (2018): 19.
• WHO’s Ambient Air Pollution database ‐ Update 2014

http://www.who.int/phe/health_topics/outdoorair/databases/AAP_database_results_2014.pdf

• Pham, D.-M.; Boussouira, B.; Moyal, D.; Nguyen, Q.L. Oxidization of squalene, a human skin lipid: A new and reliable marker of environmental pollution studies. Int. J. Cosmet. Sci. 2015, 37, 357–365

• Vierkötter, A.; Schikowski, T.; Ranft, U.; Sugiri, D.; Matsui, M.; Krämer, U.; Krutman, J. Airborne particle exposure and extrinsic skin aging. J. Investig. Dermatol. 2010, 130, 2719–2726.

• Lefebvre, M.-A.; Pham, D.-M.; Boussouira, B.; Bernard, D.; Camus, C.; Nguyen, Q.-L. Evaluation of the impact of urban pollution on the quality of skin: A multicentre study in Mexico. Int. J. Cosmet. Sci. 2015, 37, 329–338. 

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