Air pollution is a rising problem in many metropolitan areas around the world. Airborne contaminants include carbon monoxide, sulfur dioxide, nitrogen oxides, volatile organic compounds, ozone and particulate matter.
The exposure to these air pollutants is associated to detrimental effects on human skin, such as premature aging, pigment spot formation, skin rashes and eczema, and can worsen some skin conditions, such as atopic dermatitis.
Sources of pollution
Most of air pollutants are produced by the combustion of fossil fuel to produce heat and energy, major industrial processes, exhaust from transportation vehicles and agricultural sources such as livestock farms, application of fertilizers, herbicides and pesticides in crop production. Air pollution is composed of a heterogeneous mixture of compounds, categorized into two broad groups: primary and secondary pollutants. Primary pollutants are emitted directly from pollution sources, and include gases such as CO2, CO, SO2, NO, NO2, low molecular weight hydrocarbons, persistent organic pollutants like dioxins, heavy metals including lead, mercury etc. and particulate matter or PM. Secondary pollutants are formed in the atmosphere through chemical and photochemical reactions involving primary pollutants; they include ozone (O3), NO2, peroxy acetyl nitrate, hydrogen peroxide and aldehydes. Airborne particulate matter (PM) is a major concern especially in the air of densely populated urban areas; it consists of mixtures of particles of different size and composition. Depending on their aerodynamic diameter, they are commonly referred to as PM10 (<10 μm), PM2.5–10 (coarse particles, 2.5–10 μm), PM2.5 (fine particles, <2.5 μm) and ultrafine particles (UFP, <100 nm). The composition of PM varies, because they can absorb and carry on their surface a great variety of pollutants, such as gases, heavy metals, organic compounds, polyaromatic hydrocarbons, directly related to their toxicity.
Pollution induced skin damage
Being the largest organ of the human body, the skin is one of the major targets of air pollutants. Air pollution has considerable effects on the human skin, and it is generally accepted that every single pollutant has a different toxicological impact on it. Particulate Matter induce oxidative stress, producing reactive oxygen species (ROS) and causing the secretion of pro-inflammatory cytokines.
The very first step in an effective cosmetic anti-pollution routine is a proper cleansing of the skin to remove chemicals deposited on it. Another way to defend the skin against environmental stressors is the isolation of the epidermis through the formation of a cohesive and non-occlusive film on its surface, preventing the direct contact with airborne pollutants; this physical barrier can be obtained through the use of film-forming ingredients. The third approach is the inclusion in anti-pollution formulations of antioxidants, in order to protect against free radical effects, or ingredients able to up-regulate the antioxidant defenses of the epidermis cells.
Functional ingredients from botanical sources would provide relief to this issue of pollution induced skin damage.
Green tea extract
Green tea leaves contain high levels of polyphenols. Green tea is obtained by roasting or steaming Camellia sinensis (Theaceae) leaves in order to inactivate polyphenol oxidase activity. Green tea extracts are complex mixtures of bioactive compounds, including tea polyphenols, primarily green tea catechins, that account for 30–40% of the extractable solid of dried green tea leaves. Tea catechins include epicatechin, epicatechin-3-gallate, epigallocatechin and epigallocatechin gallate. These polyphenols have gained interest in recent years because of interesting biological activities, including antimicrobial, anti-inflammatory, anticancer, antioxidant and radical scavenging activities. On the basis of their biological properties, green tea polyphenols are generally accepted as having a protective effect against oxidative stress and DNA and cell structures damage induced by a number of environmental toxins/toxicants (pesticides, smoking, mycotoxins, PCB, arsenic); these properties provide the rationale for the use of green tea extracts as functional ingredients of anti-pollution cosmetics.