Air pollution and exogenous skin aging

“Human and the environment are an inseparable whole. The skin, as the outermost organ of the human body, directly contacts the external environment and is constantly challenged and invaded by environmental exposure factors. Therefore, skin aging is closely related to environmental exposure. Skin aging includes Exogenous skin aging and endogenous skin aging. Endogenous aging is genetically unalterable, and it will inevitably cause skin changes with increasing age. It mainly causes loss of skin functions due to environmental factors. The resulting skin aging is called “exogenous skin aging.” Exogenous skin aging can affect a person’s appearance, skin changes related to beauty, such as: dry skin, rough, thick and deep wrinkles, irregular pigmentation, Elastic tissue degeneration and so on are closely related to exogenous aging. Exogenous aging is also closely related to the occurrence of many skin diseases, such as solar keratosis, basal cell carcinoma, squamous cell carcinoma, etc. Exogenous aging is numerous The combined effect of environmental factors, and may be mitigated or avoided by various measures. Currently known The factors of rapid exogenous skin aging include ultraviolet radiation, heat stimulation, infrared rays, wind and sun, dry environment, smoking, etc. Among them, the effect of ultraviolet rays on skin aging is particularly important. There is more and more evidence that air pollution is also It can accelerate the aging of exogenous skin. In recent years, air pollutants such as particulate matter (PM) and skin aging caused by burning fossil fuel in kitchen have become the research hotspots in related fields. This article will focus on indoor and outdoor air pollutants and exogenous skin. A literature review of the relevance of aging.

1. Outdoor air pollutants and skin aging
1. 1 outdoor air pollutants
Outdoor air pollutants mainly include: PM, ozone, carbon dioxide, nitrogen monoxide and sulfur dioxide. PM2. 5 refers to particles suspended in air with a diameter of less than 2. 5μm, including small droplets of smoke, soot, and combustion sources, as well as particles produced by chemical reactions in the atmosphere. PM10 is a larger particle than PM2.5. The main sources of PM in urban air pollution are transportation, forest fires, and wood burning. Recent PM images have been used to obtain global PM levels. These images show that PM2.5 in northern India and China is particularly high, with an annual average of over 50ug/m3. http://www.iplbeauty.cn The presence of ozone in the stratosphere shields the effects of short-wave ultraviolet (UVC) and partial ultraviolet (UVB), but tropospheric/surface-level ozone is a secondary pollutant, which is a photochemical reaction of ultraviolet light and primary pollutants in the environment. produced. Carbon dioxide and nitrogen monoxide are mainly derived from automobile exhaust emissions from motor vehicles. Sulfur dioxide is mainly derived from the combustion of sulfur-containing fuels. Sulfur oxides and nitrogen oxides are involved in the formation of PM2.5 in the ambient air.
1. 2 outdoor air pollutants and skin aging
With the increase of air pollution in some parts of the world, people began to explore the various hazards that may be caused to the human body. Studies have shown that air pollution is associated with multiple clinical signs of exogenous skin aging. Vierktter et al. studied the relationship between exposure to atmospheric particulate matter (mainly PM10) and skin aging. The study selected 400 Caucasian women aged 70-80 years from developed industrialized areas and less polluted villages. The area mainly investigates the effects of traffic-related soot and particulate matter on skin aging in different regions, and SCINEXA is used to score the degree of skin aging. The study found that more than 35% of the stains were correlated with air pollutants in the adjacent (< 100m) busy main road (> 10,000 vehicles/day). The stain on the forehead and cheeks is correlated with long-term exposure to smoke, traffic particles, and PM10. Each additional IQR of soot can increase the forehead and cheek spots by 20%. The incidence of pigmentation in Indians and Southeast Asians with skin types of type III and type IV is high, and it is the main clinical marker for premature aging of Asian skin. Another study in Mexico found that people living in heavily polluted areas had significantly lower levels of vitamin E, squalene, and interleukin-1, while elevated lactate levels. Squalene is an important endogenous antioxidant, while vitamin E is the main exogenous antioxidant. The reduced results indicate that they are mobilized to fight oxidative damage to the skin, suggesting that air pollution causes the skin to oxidize. Stress state.
1. 3 PM and skin aging related mechanisms
Air Pollutants How PM has caused skin aging has just begun, and its effects on the skin may be based on several mechanisms.
1. 3. 1 carrying polycyclic aromatic hydrocarbons
These particles can carry organic compounds such as polycyclic aromatic hydrocarbons (PAH) into the body, which are extremely lipophilic and easily penetrate the skin. As early as 2008, a German study found that polycyclic aromatic hydrocarbons can induce melanocyte proliferation and skin pigmentation in mice. Polycyclic aromatic hydrocarbons are highly efficient ligands for keratinocytes and melanocyte-expressing ligand-dependent transcription factors, the aromatic hydrocarbon receptor (AhR), possibly through the expression of tyrosinase and tyrosinase-related protein 2 genes. To regulate the formation of epidermal melanin. Polycyclic aromatic hydrocarbons are exogenous ligands for aromatic hydrocarbon receptors. They activate reactive oxygen species (ROS) after activation of aromatic hydrocarbon receptors. ROS-mediated oxidative damage involves a large number of molecules, causing DNA modification and lipid peroxidation. And the secretion of inflammatory factors. There are many internal and external causes that can generate free radicals such as: environmental pollution, sun exposure, self-stress, smoking, and daily metabolic processes. There is evidence that free radicals can destroy the expression process of genes, degrade collagen fibers, and can also cause accumulation of elastin-like substances, leading to signs of skin aging.
1. 3. 2 directly into the skin
Particulate matter can enter the skin through channels such as follicular pores, wounds, and incomplete skin barriers, directly causing allergies, oxidative stress, and inflammatory responses [5,18]. 1. 3. 3 Contaminants synergize with other factors such as sunlight We know that under natural light, the skin is exposed to both UV and IR, causing damage to collagen and elastin. Recent studies have confirmed that large amounts of air pollutants can multiply the skin aging process caused by daylight exposure. The combination of UVA with environmental pollutants such as PM and PAHs can effectively accelerate exogenous skin aging. The MC1R gene is a gene that determines hair and skin color in the human body. Elf-akir A found that in the 524 French women enrolled in the study, there were two functional deletions of the MC1R mutant (R151C, R160W, R142H, D294H, I155T, D84E). Women are 6 times more likely to develop a serious risk of skin aging than women who carry both WT alleles. Among them, carrying R142H, R151C, D84E has the highest risk. The study also confirmed that the mutated MC1R gene can significantly aggravate age-related skin aging and, to a certain extent, promote skin aging caused by environmental pollution.
1. 4 Mechanisms related to ozone and skin aging
There are currently few studies on the correlation between ozone and skin aging. Stratospheric ozone absorbs and scatters ultraviolet light, and its concentration decreases the amount of UV radiation reaching the ground, especially UVB, which can cause serious damage to the skin. However, ozone at the surface level is a highly unstable molecule that acts specifically on the surface of the skin and easily oxidizes the molecules of the stratum corneum of the skin. In vitro experiments have shown that ozone concentration close to the concentration of ozone in ambient air pollution can lead to vitamin E and vitamin C deficiency in the epidermis, while producing epidermal malondialdehyde (a lipid peroxide) on the surface. Malondialdehyde causes an increase in hydrogen peroxide concentration, decreased ATP levels, increased IL-1a release, induced pro-inflammatory markers (COX-2), heat shock proteins (HSP32, 70, 27), NF in epidermal keratinocytes. Characterization of -KB and matrix metalloproteinase MMP regulation, and DNA damage caused by oxidative stress.

2. Indoor air pollution and skin aging
The main indoor pollution comes from the burning of smoking and kitchen fossil fuels.
2. 1 smoking
Smoking is not only harmful to the body, but also increases ambient air pollution. Numerous studies have shown that smoking is an independent factor in skin aging. Smoking is associated with upper lip lines, sun-elastic tissue deformation, telangiectasia, and sagging skin. The 40-year-old population with long-term smoking habits is similar to the non-smoking 70-year-old population. Smoking causes premature skin aging. Tobacco is a complex mixture of pollutants, similar to air pollution, which can affect the metabolism of collagen. Collagen reduction can lead to decreased skin tension, which can cause skin aging, especially wrinkles. At the same time, smoking also increases the content of elastin and metalloproteinases. Recently, studies have found HMGB1 protein in the cytoplasm of epidermal keratinocytes of mice. The increase of HMGB1 protein leads to the loss of collagen, which is negatively correlated. The HMGB1 protein was more abundant in the mouse epidermal keratinocytes that survived for 4 weeks in the second-hand smoke environment. In 2015, Suzaynn proposed the concept of “three-handed smoke”, which is released into the indoor or public places by PAHs, nicotine, cotinine, and tobacco-specific nitrosamines produced by smoking, and remains on the surface of the room or cotton fabrics worn. Upper (concentration 10 times higher than the control group), forming a three-handed smoke, and entering the body through the skin or respiratory tract, causing damage to the body.
2. 2 kitchen fossil fuel
Recently, Li et al. studied the relationship between kitchen fumes and skin aging in Chinese. They selected women between 30 and 90 years old in Pingding (Northern China) and Taizhou (Southern China). The degree of skin aging was scored using SCINEXA. The results show that kitchen fossil fuel combustion increases the risk of 5% to 8% of facial wrinkles and 74% of hand wrinkles. There is not much report on the mechanism of fossil fuel combustion to accelerate skin aging, but fossil fuel combustion can produce PAHs, in which Benzo[a]pyrene (Ba P) is a result of insufficient combustion of fossil fuels. PAHs, which remain in the air, food, and water. In a mouse experiment in 2009, it was confirmed that Ba P exposure can cause oxidative DNA damage, leading to the formation of 8-OHdG and H2O2. The oxidative DNA damage produced by Ba P plus UVA exposed mice was 14 times higher than that of mice exposed to Ba P or UVA alone.

3. Summary and outlook
Indoor and outdoor air pollutants, like UV light, can accelerate skin aging and are associated with the formation of signs of exogenous skin aging. Since exogenous skin aging associated with air pollution is associated with oxygen free radicals, oral antioxidants and topical antioxidants may be effective means of combating air pollution-related aging. External use of antioxidant creams and thorough cleansing of the face before going to bed can reduce the direct contact of air pollutants with the skin. After cleansing, use products containing antioxidants to protect the skin, which can delay the exogenous skin aging caused by air pollution. “