Dull complexion: the impacts of pollution on skin radiance.

Whether it originates naturally or is man-made, pollution has significant effects on human health, as well as on the skin. There are numerous sources of pollutants, which can be either natural or anthropogenic, including swamps, biological decomposition, thermal power plants, and the incineration of household and industrial waste. Even though air pollution is most prevalent in urban environments and activity zones, rural areas are by no means spared. It should be noted that the main atmospheric pollutants that affect the skin are polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds, nitrogen oxides, airborne fine particles, ozone, and heavy metals.

Chronic exposure to increasing amounts of all these forms of pollutants compromises the integrity and radiance of the skin.

In fact, environmental pollutants are responsible for increasing oxidative stress in skin cells. This manifests as an intensification in the production of free radicals and reactive oxygen species, through the peroxidation of polyunsaturated fatty acids, notably found in the hydrolipidic film, and through the depletion of the skin's endogenous antioxidant capacity, relying on the activities of enzymes, such as glutathione peroxidase and catalase, but also on antioxidants naturally present in the skin, like vitamin C and vitamin E. However, when the skin's antioxidant defence potential is exceeded, meaning that the cells can no longer eliminate the free radicals, a series of reactions are set in motion, notably impacting the uniformity of the complexion.

Indeed, free radicals generated by pollution can damage various skin organelles, including keratinocytes, the constituent cells of the epidermis. Oxidative stress can particularly alter the DNA and mitochondrial activity of keratinocytes, thereby disrupting their ability to proliferate and potentially leading to a slowdown in cellular renewal. This slowdown results in an accumulation of dead cells on the skin's surface, forming a thick and irregular horny layer. This agglomeration prevents light from reflecting properly on the skin, giving it a dull and tired appearance.

Furthermore, studies have shown that carbon monoxide, originating from the incomplete combustion of organic materials, such as natural gas, wood, coal, petrol or even oil, can bind to the haemoglobin of red blood cells and alter its conformation, thereby reducing its ability to transport oxygen. Indeed, the affinity of carbon monoxide for haemoglobin is 210 to 260 times stronger than that of oxygen. Even when present in minute quantities in the air, carbon monoxide will preferentially bind to the haemoglobin in the blood instead of oxygen. This decrease in oxygenation is also felt at the level of skin cells. This oxygen deficit, or hypoxia, can lead to a reduction in the production of keratinocytes, an accumulation of dead cells and, consequently, a lack of skin radiance.