How to protect your skin from pollution?

It has long been recognised that environmental exposures affect skin health. UV radiation is the most studied environmental risk and its effects on the skin are well established. The ambient air pollution is another potentially serious environmental aggressor. Numerous studies in vivo and in vitro reveal that air pollution, both ambient (outdoor) and domestic (indoor), is directly attributable to the emergence of a wide range of dermatological disorders, such as dry skin, sensitised skin, loss of firmness, brown spots, dull complexion, wrinkles and fine lines, worsening of acne and inflammation.

Based on current data, four potential mechanisms can explain how various pollutants (particles, nitrogen oxides, sulphur oxides, ozone and polycyclic aromatic hydrocarbons) can damage the skin: the generation of free radicals (oxidative stress), the induction of an inflammatory cascade and disruption of the skin barrier, the activation of the aryl hydrocarbon receptor (AhR) found on several types of cells (keratinocytes, melanocytes, fibroblasts, Langerhans cells) and the alteration of the skin microflora. Furthermore, due to the development of industrialisation and the use of transport, the effects of air pollution on human health have increased logarithmically in recent years. It is estimated that nine out of ten people are exposed to polluted air every day.

The first approach involves removing pollutants that have settled or penetrated the skin in order to prevent or mitigate their impact. The use of cleanser, exfoliant or mask can help to reduce this particle load on the skin, an action largely conferred by the presence of surfactants in the formulation. However, the chosen surfactant should not be harsh on the skin, as this could lead to an increase in the penetration of pollutants into the skin's pores. Furthermore, due to their adsorbent properties, certain active ingredients are added to cleansing products to help remove accumulated impurities.

Examples of active ingredients?

• The activated charcoal (INCI: Charcoal Powder) is a hydrophobic material known for its high adsorption power, a process that relies on intermolecular attraction forces. Indeed, it is capable of retaining and fixing certain substances on its surface. This adsorption capacity is primarily due to its network of pores and its large specific surface area.

• Whether it's red, yellow, white, green... theclay (INCI: Kaolin/Illite/Montmorillonite) has a natural adsorption capacity. When applied to the skin, it acts like a "magnet" by attracting and capturing on its surface the environmental pollutants embedded in the pores through electrostatic interaction.

Note : Over-cleaning one's skin is not the solution. On the contrary, excessive washing can further damage the skin's natural protective property and provide an entry point for pollutants.

Environmental pollutants can induce oxidative stress and produce free radicals, which can damage proteins, DNA, and cell membranes. This phenomenon results in wrinkles and fine lines, redness, dehydration, and volume loss. However, the use of antioxidants and metal-chelating agents in skincare formulation can provide an alternative strategy to counteract or prevent these induced harmful effects.

In a study, researchers evaluated the protective effects of a blend of antioxidants (15% L-ascorbic acid + 1% α-tocopherol + 0.5% ferulic acid) against damage caused by ozone-induced oxidative stress in human keratinocytes. The results showed that this treatment protects cells from ozone-induced cytotoxicity, and reduces the formation of peroxidised lipids and reactive oxygen species (ROS). Additionally, an activation of Nrf2 and a regulation of the NF-κB signalling pathway were observed.

Here is a diverse selection of active ingredients that have demonstrated their protective effects:

• Theferulic acid is the most common derivative of cinnamic acid, which has antioxidant activity and a protective role for the main structures of the skin (keratinocytes, fibroblasts, collagen, elastin). It acts as a free radical scavenger through electron and hydrogen transfer, but also as an inhibitor of enzymes that catalyse the generation of free radicals and an enhancer of the activity of antioxidant enzymes.

• Thephytic acid is a natural plant-based inositol hexaphosphate that constitutes 1 to 5% of most cereals, nuts, legumes, oilseeds, pollen, and spores. It is a potent inhibitor of the formation of iron-induced hydroxyl radicals, as it can form a unique iron chelate that becomes catalytically inactive. Phytic acid can also effectively inhibit lipid peroxidation.

• The carotenoids, such as β-carotene, lutein, zeaxanthin, and astaxanthin, also form part of the cellular defence system against free radicals. Indeed, they are capable of binding peroxyl radicals (ROO°) in order to stabilise them through their system of conjugated double bonds, thereby inhibiting the propagation of chain oxidations.

• The phenolic compounds (polyphenols), derived from various plants, mitigate the cellular oxidative stress induced by pollutants. Their antioxidant power is attributed to their ability to trap free radicals by transforming them into more stable compounds through the donation of an electron or hydrogen atom, conferred by their aromatic structure, to chelate metallic ions, to reduce their production by inhibiting the activity of oxidation enzymes (xanthine oxidase, peroxide oxidase, lipoxygenase, etc.) and to enhance the cellular antioxidant capacity. Among the most commonly used phenolic compounds are quercetin, found for example in red onions and capers, resveratrol primarily found in grapes and Japanese knotweed, and curcuminoids contained in ginger and turmeric.

• Theginseng extract (INCI: Panax Ginseng Root Extract) contains high levels of ginsenosides (around 30%), which gives it a strong antioxidant capacity. They could neutralise up to 80% of free radicals, protecting cell membranes and helping the skin to defend itself against pollution and other environmental aggressions

• The niacinamide is a water-soluble vitamin with antioxidant effects that aids in repairing damaged DNA. A study has revealed that niacinamide has inhibitory properties on the generation of ROS induced by PM2.5, as well as preventing the oxidation of molecules, such as lipids, proteins and DNA, induced by PM2.5.

• Phytosterols (plant sterols) are found in various oils derived from the seeds, roots, stems, leaves, and fruits of plants. They have proven useful in reducing the production of ROS, inflammatory responses, and cellular damage caused by particles. For example, fucosterol, a sterol that can be isolated from seaweed, increases the expression of antioxidant enzymes and manages to regulate the NF-kB and MAPK signalling pathways, thus reducing the levels of pro-inflammatory cytokines.

• The vitamin C (INCI: Ascorbic Acid) is a water-soluble vitamin that aims to limit cell damage by acting as a reducing agent. Unstable, synthetic forms of vitamin C can be used, such as ascorbyl palmitate (INCI: Ascorbyl Palmitate), sodium ascorbyl phosphate (INCI: Sodium Ascorbyl Phosphate ), ascorbyl glucoside (INCI: Ascorbyl Glucoside) and tetrahexyldecyl ascorbate (INCI: Tetrahexyldecyl Ascorbate).

• The vitamin E (INCI: Tocopherol) is a term that encompasses a group of eight organic molecules: four tocopherols and four tocotrienols. Only the α-tocopherol meets human needs for vitamin E. It is capable of capturing and stabilising peroxyl radicals produced during lipid peroxidation, which leads to the formation of a neutral species, thus reducing their harmfulness.

A well-hydrated skin with a strengthened skin barrier is better equipped to combat pollution. Emollients aid in enhancing the skin's barrier function to reduce the skin penetration of pollutants by forming a physical protective layer. Moreover, their use helps to decrease the adherence of pollution particles to the skin's surface. Indeed, emollients create a smooth surface, making it more challenging for particles to attach and accumulate on the epidermis.

Examples of active ingredients?

• Thepolyglutamic acid helps to strengthen the skin barrier, which is essential for preventing the penetration of harmful substances into the skin, thereby reducing potential damage. Indeed, this biopolymer forms a microscopic film (microgel) on the surface of the epidermis, thereby enhancing the impermeability of the skin barrier.

• The ceramides constitute a significant part of the structure of the skin's intercellular lipids, forming a protective barrier against external aggressions, including pollution. They help to maintain the integrity of the skin barrier by filling the spaces between the cells of the stratum corneum, creating a solid and cohesive structure. A strengthened skin barrier limits the penetration of pollution particles and other harmful substances into the skin.

• Theextract of tremella (INCI: Tremella Fuciformis (Mushroom) Extract), rich in polysaccharides, possesses intense hydration properties and forms a light film on the skin's surface. It thus protects the skin from pollution and provides a superior moisturising effect.

• Acting as a second skin, thered algae extract (INCI: Carrageenan, Maris Salt (Sea Salt)) forms a shield-like film to protect the skin from environmental aggressors, due to its high carrageenan content. It thus provides immediate hydration and a soft touch. Furthermore, red algae extract has the ability to stimulate the natural synthesis of ceramides, lipids organised into dense and structured lamellae that form the intercellular cement, thereby strengthening the skin's barrier.

Another measure to enhance skin protection is to use a broad-spectrum sunscreen (UVA/UVB) to prevent photo-reactive compounds, as has been described for particles and polycyclic aromatic hydrocarbons (PAHs), from reacting with UV rays. Indeed, there is evidence that UV rays can potentiate the harmful effects of pollutants on the skin. In other words, dermatological risks can be amplified by the possible synergy between air pollution and sun exposure, particularly to UVA rays.

Tinted skincare products can also provide a certain level of protection against pollution. When applied to the skin, they form a physical barrier between the skin and the external environment due to the presence of pigments in the formula. This can help to reduce the direct contact of pollutants on the skin and prevent their accumulation, thereby limiting their impact. A uniform application and a sufficiently thick layer will optimise the formation of this protective barrier.

If the skin's response to pollution occurs both through surface interactions and contamination of the deeper layers of the skin from within, prevention strategies should combine products capable of protecting at both these levels. Thus, dietary supplementation may also prove beneficial. One study showed that taking β-carotene orally for a month protected the skin of hairless mice against chronic exposure to ozone (0.8 ppm 6 hours/day for 7 days).

Contrary to popular belief, indoor air is more polluted than outdoor air. Therefore, air purifiers can be beneficial as they trap suspended particles in the ambient air (fine particles, allergens, chemical pollutants, etc.), thus limiting their impact on the skin. Their operation depends on the filtration system.

• Mechanical Filtration: Most air purifiers utilise this filtration system, which involves trapping airborne particles using a filter (pollens, allergens). The most commonly used filters are HEPA filters (High-Efficiency Particulate Air). They are designed to capture small-sized particles. In fact, the air is drawn in and then passes through the HEPA filter, and the particles are thus retained, allowing the purified air to return to the room.

• Activated Carbon Filtration: Some air purifiers also utilise activated carbon filters in conjunction with HEPA filters. Activated carbon is a porous material that has the ability to adsorb gases and chemicals present in the air, including volatile organic compounds (VOCs) and toxic chemicals.

• Ionisation (Photocatalysis): Some air purifiers utilise ionisation technology to remove contaminants from the air. They emit negative ions (anions) into the air, which bind to airborne particles, making them "heavier". This allows the particles to be drawn towards the ground and no longer remain airborne, thus facilitating their removal during cleaning.

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