Skin & pollution: What we know today

The 2012 WHO Air Pollution Report published data identifying air pollution as the world’s largest single environmental health risk.

As well as environmental pollution’s well-known cardiovascular and respiratory impacts, evidence of its damaging effects on human skin is growing:^1,2

In 2010, an epidemiological, cross-sectional study conducted in Germany (SALIA: Study on the Influence of Air pollution on Lung function, Inflammation and Aging) showed that chronic traffic-related particulate matter (PM) exposure is significantly associated with extrinsic skin aging, particularly pigment spot formation.¹

More recently, indoor air pollution was shown to be associated with coarse wrinkle development in two Chinese cohorts.¹

Pollution may trigger or worsen skin conditions¹

Ambient pollution may not only affect healthy skin, but also exert detrimental effects on diseased skin as shown by several epidemiological studies:

Mechanisms of action remain to be fully elucidated¹

From a theoretical point of view, pollution’s deleterious effects on the skin may be due to

• An outside-inside effect, e.g. penetration of PM and/or organic compounds bound to PM into the skin
• Or an inside-outside mechanism: PM exposure may cause systemic effects as a consequence of:
  • Particles penetrating the lung and subsequently the circulation and possibly from there affecting the skin.
    And/or by causing an inflammatory reaction in the lungs, which may subsequently cause systemic inflammatory reactions that are also detrimental to the skin.

Current research suggests that each individual air pollutant has a specific, toxic action on the skin.

• On intact skin:
  • Ozone is a highly unstable molecule that exclusively targets the skin surface and thus does not exert direct effects on viable skin cells. It mainly acts on the stratum corneum in which it readily oxidizes with molecules.1
    In contrast, organic compounds present on the surface of PM may penetrate into the skin and have direct effects on viable skin cells such as keratinocytes and melanocytes, e.g. by binding to the AhR. This may lead to the gene expression relevant to skin aging and pigmentation and to oxidative stress causing skin inflammation.¹
• On barrier deficient skin: particles may penetrate and cause oxidative stress and skin inflammation.¹

Current model of pollution-induced skin damage (from Krutmann J, et al. Pollution and skin: From epidemiological and mechanistic studies to clinical implications. J Dermatol Sci (2014)¹
(AhR, aryl hydrocarbon receptor; COX-2, cyclooxygenase-2; ICAM-1, intercellular adhesion molecule-1; IL1a, Interleukin 1a; IL6, interleukin 6; MITF, microphthalmia-associated transcription factor; MMP, matrix metalloproteinase; O3, ozone; PAHs, polyaromatic hydrocarbons; POMC, pro-opiomelanocortin; PM, particulate matter; ROS, reactive oxygen species; UV, ultraviolet, VOC; volatile organic compounds.)

Going further

To learn more about pollution^1,3

Pollution is a contamination of the indoor or outdoor environment by any chemical, physical or biological agent.
Outdoor pollution comes from a combination of fixed sources, such as factories, and mobile sources, such as road and air traffic.

This combination produces primary and secondary pollutants:

• Primary pollutants can be divided into two groups:
  • Particulate matter (PM) commonly referred to as ultra-fine, fine or coarse particles (UFP, PM2.5, PM10); small particles are produced by combustion and larger ones by mechanical processes that create and then suspend dust particles in the wind. Gases (CO₂, CO, NO₂, NO, NOx, SO₂) or volatile organic compounds.
• Secondary pollutants such as ozone and peroxyacetyl nitrates are formed from photochemical reactions between primary pollutants, heat and UV radiation. These pollutants stay low in the atmosphere (troposphere) and settle over both urban and rural areas, forming what is typically known as smog.

NB: Classification of air pollutants by the Environmental Protection Agency (USA): – lead (metal & industrial processing plants); – particulate matter (soot, exhaust, industry); – nitrogen oxide and carbon monoxide (car exhaust); – sulphur oxide (industrial plants); – ground level ozone (result of a photochemical reaction between O₂ and pollutants such as hydrocarbons and nitrous oxides, facilitated by sunlight).