May 15, 2020 Skin 101
Air Pollution and the Skin
This is by far one of our favourite timely and relevant articles by our Resident Scientist: Giorgio Dell'Acqua. It affects us all and brings to light the fact that air pollution and how this affects our health and skincare regimes must be considered.
Air pollution is from industrial waste that originates from fossil fuel combustion, vehicle gas exhaust, and environmental elements
such as sunlight (UV), heat, humidity, ozone, dust, and soot
that can synergize and further activate pollutants or function as pollution carriers. The high level of air pollution measured in large cities
(such as New Delhi, Beijing, Mexico City, etc.) and the visual presence of it (pollution clouds, haze) together with constant warnings and safety indications from authorities
(daily pollution level information, use of masks and protective gear, anti-pollution products and devices, etc.) have created a strong awareness in the general population about air pollution
, raising concerns of the possible long- and short-term effects of air pollution on general health.
Air pollution is recognized as a global health threat. Recent statistics from the World Health Organization report that in 2012 around 7 million people died as a result of air pollution exposure .1
More than four in ten Americans (almost 150 million) live in counties that have unhealthy levels of ozone or particle pollution
, 2 and more than 90% of people in European cities breathe dangerous air .3 In quickly developing countries such as India, China, and Mexico, with increasing population (and transportation) and industrial waste, air pollution is now a primary health care concern.
Scientific evidence and clinical studies around the globe suggest air pollution is a primary damaging factor in skin. 4-9 Clinical studies in Germany, Korea, and China have demonstrated a link between air pollution and skin damage. Particulate matter (PM), volatile organic compounds (VOCs) and ozone (O3) are the principal pollutants involved in damage to skin tissue.
Subjects living in polluted areas showed visible and physical skin damage. In Germany, individuals living in industrial areas with high levels of PM had increased skin pigmentation (dark spots) and wrinkle formation (nasolabial furrows) as compared to people living in rural areas and not exposed to PMs .10 In Korea, seasonal fluctuations of air pollutant concentrations
(such as PM, oxides, andVOCs) correlated with exacerbation of atopic dermatitis (AD) symptoms and barrier dysfunction in AD patients .8 In China, O3 pollution exposure in 70,000 individuals over a period of two years correlated with increased AD, eczema, and pruritus .11 Principal Pollutants in the Skin Particulate Matter (PM) PM is a mixture of very small particles and liquid droplets.
They are characterized as PM 10 (larger than 2.5 micrometers and smaller than 10 micrometers in diameter) and PM 2.5 (2.5 micrometers in diameter and smaller), and are composed of a number of elements including acids, organic chemicals, metals, soil, and/or dust particles.
PM 10 accumulates near roadways and dusty industries. PM 2.5 is found in smoke and haze, and can form by oxidation of combustible gases .12 Although still debated, PM2.5 can penetrate the skin either through the pores or trans-epidermally .10 In fact, pore diameter is on average about 50-80 micrometers. PM2.5 could act as a vehicle for toxic pollutants such as heavy metals (cadmium and lead), oxides, organic compounds, bacteria, and viruses.
Toxic pollutants adhering to the fine particle would diffuse through the skin inducing oxidative stress with consequent skin barrier damage and delayed skin repair .10 .13 Indeed, clinical studies on subjects living in polluted areas with a high daily level of exposure to PM found increased visible skin damage (dark spots and wrinkles) and reduced barrier function .10
Carbon monoxide (CO), sulfur dioxide (SO2) and nitrogen oxide (NO2) are pollutant gases. CO is produced by vehicle exhaust, but it also occurs
naturally during wildfires and volcanos. SO2, on the other hand, is created by burning coal and petroleum. NO2 production stems from high temperature combustion of fuel, and like CO, is a good indicator of traffic-related pollution.
Oxides, such as NO2, induce free radical formation causing skin protein and lipid damage.14 Clinical studies comparing children living in urban versus suburban areas found a strong correlation between the high level of outdoor oxides (related to traffic exhaust gases) and increased prevalence of skin sensitization (atopic dermatitis and allergies) .15-17
- Volatile Organic Compounds (VOCs)
VOCs are emitted as gases from certain solids or liquids.
VOCs include a variety of chemicals emitted from paints, cleaning products, pesticides, building materials, copiers, printers, correction fluids, glues, etc.
VOCs are also typically associated with indoor pollution as many chemicals present and used in the household or the office contain organic solvents
that emit VOCs. Also, VOCs in combination with oxides (e.g., NO 2) and sunlight cause the formation of O3 at ground level.
This phenomenon is commonly known as photochemical smog .18 Studies suggest that transdermal uptake of VOCs is comparable to exposure during inhalation .19 Skin exposure to VOCs leads to an increase of trans-epidermal water loss
(TEWL) and increased skin reaction to allergens, suggesting an altered skin barrier .20
- Polycyclic Aromatic Hydrocarbons (PAHs)
Polycyclic aromatic hydrocarbons (PAHs) are chemicals that occur naturally in coal, crude oil, and gasoline.
They also are produced by combustion of coal, oil, gas, wood, garbage, and tobacco.
PAHs generated from these sources can bind to or form small particles in the air. High-temperature cooking will also form PAHs
in meat and in other foods. Cigarette smoke also contains many PAHs.
PAHs are frequently bound to the surface of PM.21
Toxic organic compounds such as PAHs induce free radical formation to generate oxidative damage in the skin .22
But they can also activate the aryl receptor (Ahr). Ahr is involved in the response to environmental stress, .23 .24
and its activation by PAHs induces skin inflammation .25
and skin aging .27
Exposure to PAHs bound to PM has been postulated as the cause of increased melanin spots in subjects living in industrial areas exposed to high PM levels .8 Although O3 is mostly known as the gas in the stratosphere (ozone layer) that forms a shield around the Earth, keeping out most of the UV radiation from the Sun (UVC and most of the UVB), it is also a powerful oxidant when found at ground level (troposphere). Ozone in the troposphere can in fact form from the chemical reaction between ground pollutants (VOCs and oxides) in the
presence of sunlight.
O3 induces formation of reactive oxygen species (ROS), such as H2O2, as well as lipid peroxidation products, which trigger skin oxidation with consequent skin damage.28 Although the skin possesses antioxidants and barrier protection mechanisms to fight O3-induced oxidation, experimental studies have shown that O3 is able to rapidly deplete levels endogenous antioxidants in skin (vitamin C, vitamin E and glutathione) .29-31 and induce the production of pro-inflammatory markers (e.g., cyclooxygenase-2 and nuclear factor-kappa B) .31 This effect was correlated with skin barrier damage and an inflammatory response .30 In clinical studies, O3 exposure was correlated to an increased manifestation of atopic dermatitis, eczema, and pruritus .32 O3 also affects the dermis of the skin by upregulating matrixmetalloproteinase-9, resulting in consequent skin degradation .31 Finally, O3 has been associated with Ahr activation33 leading to pigmentation and skin aging .23, 26
It has been shown that in the presence of UV the damaging effects of pollutants on the skin worsen
- UV Synergizes with Pollution
, particularly in the stratum corneum .28,34
In combination, UV and O3 also produce an additive effect in terms of antioxidant depletion and lipid peroxidation induction .35
Epidemiological studies suggest that the response to air pollutants is age related .36 Experimental evidence demonstrates that older skin experiences higher oxidative stress, as compared to younger skin, when exposed to O 3or cigarette smoke (
containing VOCs and PAHs).37
This stress is associated with an increase in oxidized proteins, oxidized lipids, and inflammatory markers as well as greater activity of skin degrading proteases .38
Furthermore, in mice models for skin wounds, older skin exposed to O3 has a significant delay in wound healing comparing to younger skin.39
This evidence—although still experimental and only tested on a few pollutants—suggest a less robust reaction to pollutants by older skin. DOWNLOAD THE PDF FROM GIORGIO'S WEBSITE HERE
Our Founder Natacha Paugam tackles this topic in a different blog here, citing the Effects of Air Pollution on the skin when traveling and seeing the world from a different perspective About the Author (our Resident Scientist)
Giorgio Dell’Acqua, Ph.D. Giorgio has spent the last 17 years as an executive and cosmetic scientist in the personal care industry. He is specialized in skin and hair care ingredients, finished product development, and technical marketing. Dr. Dell’Acqua has covered multiple roles as a manager and director in different companies specialized in active ingredients and product development. He has helped bring more than 200 successful active ingredients and finished products to market and has authored more than 60 publications in medicine and cosmetic science. In the last 10 years Giorgio has been writing and lecturing on natural cosmetic ingredients and sustainable supply chain, as well as helping to source, develop, and bring to market many natural ingredients. He is an award winning speaker on natural ingredients, a regular columnist on sustainable cosmetic science, and an adjunct professor in Cosmetic Science at Fairleigh Dickinson University. He is also the chair of the Scientific Affairs Committee for the New York Society of Cosmetic Chemists and its scientific blogger.
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