The skin is the first line of defense against environmental aggressors. Although UV radiation is best known, other sources such as pollution have become topics of concern. Pollution is a common concern in Asia, where nearly 90% of big cities have substandard air quality.^1,2 Environmental contamination can affect air, water and land. Air pollution is mostly due to fossil fuel combustion, but it can also be present indoors due to household activities such as biomass burning for cooking or heating and tobacco smoking.³ Sources of water contamination include agricultural and industrial work or by-products of water purification procedures, sometimes found in potable water.⁴ Pollution can also be derived from the direct deposition of air contaminants into water or from land pollution via infiltration of soil contaminants into groundwater. 


The main contaminant components from the environment that the skin encounters involve gaseous pollutants, volatile compounds, toxic metals and particulate matter (PM), a complex mixture of harmful micro-particles and liquid droplets classified according to their size; e.g., PM₁₀ and PM_2.5.These substances can have deleterious effects on the skin, inducing premature aging and irritation. They also drive the production of free radicals able to react and decrease the functionality of biological molecules, such as lipids due to peroxidation. Exposure to environmental aggressors also leads to metallothioneins synthesis, which are metal-binding proteins with a role in heavy metal detoxification and free radical scavenging.⁵ Furthermore, epidermal Langerhans cells decrease in density, with a consequent decline in skin immunity. These cells are in charge of taking up pollutants, while migrating away from the epidermis toward lymph nodes, where they present foreign antigens to initiate the immune response.

 
Even though the skin has a certain ability to protect itself from the environment, it can be overcome when in contact with excessive levels of chemical stressors. Overexposure to contaminants leads to a reduction in the skin’s intrinsic antioxidative defense, causing oxidative stress and consequent tissue damage.

 
The penetration of particles carrying organic pollutants and toxic metals can be avoided by topically smearing protective films or by applying molecules such as metal chelators to reduce the direct contact of contaminants with the skin. It is also important to complement the loss of the skin’s own antioxidants by providing an external supply. Topical formulations can result in potential solutions to enhance the skin’s own protection against contaminants and minimize their effects on the skin, while improving the appearance of most pollution-exposed skin areas.

 
The cosmetic ingredient called Pollushield functional ingredient (INCI name: Water (aqua), propanediol, diisopropyl adipate, lecithin, acrylic acid/acrylamidomethyl propane sulfonic acid copolymer, dimethylmethoxy chromanol, glyceryl caprylate, xanthan gum) is a combination of a polymer with metal chelating properties with a powerful antioxidant to scavenge free radicals. This anti-pollution ingredient helps provide a barrier between the skin and pollutants, while boosting the antioxidative potential of the skin.

 
Metal Sequestering


An in vitro assay was performed to assess the ability of the ingredient to scavenge heavy metals. The active ingredient was mixed at a 5:95 ratio with a solution of metals containing lead (Pb), nickel (Ni), zinc (Zn) and iron (Fe), each at 1ppm. The resulting mixture, containing 5% cosmetic ingredient, was incubated for six hours at room temperature. After dialization of the mix, metals bound to the cosmetic ingredient were measured by inductively coupled plasma mass spectrometry. Results showed a capacity to capture between 87% and 97% of metal particles exposed to the ingredient.


 
Urban Dust Protection


Protection from urban dust was evaluated on human epidermal keratinocytes from adult (HEKa), which were incubated with acrylic acid/acrylamidomethyl propane sulfonic acid copolymer and dimethylmethoxy chromanolat concentrations equivalent to 0.5% of the cosmetic ingredient. Non-treated cells were used as a control. Following incubation, 100µg/ml urban dust, consisting of atmospheric particulate material collected in a city, were added and incubated with the cells. After 24 hours, cellular viability was evaluated through a colorimetric method based on the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), resulting in a 47.9% higher viability when treated with the active ingredient and compared to control (p<0.0001).


 
Anti-Pollution Activity


Human skin explants maintained with culture medium were treated with 5% anti-pollution ingredient in a carboxymethyl cellulose (CMC) aqueous gel (which gives the ingredient an appropriate viscosity to stay in contact with the skin) or with the CMC aqueous gel alone. The two gels were applied once a day during four days. Non-treated explants were used as a control. Then, four hours after the last treatment, the explants were exposed to a pollution mix that contained heavy metals, hydrocarbons and diesel particles, for 24 hours. Different parameters were evaluated:

• Skin morphology. Skin sections were stained following Masson’s trichrome, Goldner variant method. Morphology of tissue and cells was visually evaluated by a trained expert. The cosmetic ingredient showed to help preserve normal morphology in pollution-exposed skin, maintaining density of the dermal collagen network (green staining) and typical morphology of epidermal and dermal cells (purple staining) (Fig. 1).
 
  
• Expression of metallothionein.Protein metallothionein (MT-1H) was used as a marker of exposure to metals and oxidative stress. This protein was visually evaluated by trained experts and detected on skin tissue sections by means of immunostaining (Fig. 2). MT-1H was not increased despite exposure to toxic substances, suggesting skin protection by the active ingredient.
 
  
• Quantity of Langerhans cells: Glycoprotein CD1a, which is specifically expressed by Langerhans cells, was detected through immunostaining and quantified on skin tissue sections (Fig. 3). The total amount of Langerhans cells diminished significantly when exposed to pollution. However, with the anti-pollution ingredient, the number of these cells was 32.4% higher compared to non-treated pollution-exposed skin (p<0.05), showing a preservation of such cells despite exposure to pollution.


• Lipid peroxidation: An enhanced method of the thiobarbituric acid reactive substances (TBARS) assay was used to assess the degree of skin lipid oxidation. The concentration of the marker for oxidative stress malondialdehyde (MDA) in the explants medium was quantified, resulting in a reduction of 37.4% (p<0.05) in pollution-exposed skin pretreated with the ingredient compared with non-treated skin.
 

Skin Protection from Urban Pollution


A clinical test was performed in a panel of 20 Asian female volunteers (26-62 years old), who were outdoor workers in Beijing. These subjects applied a placebo cream to half face and a cream containing 5% cosmetic ingredient to the other half.The barrier effect against pollutants and the antioxidative efficacy of the ingredient were measured on skin samples obtained through tape stripping.


• Barrier effect against pollution: At the beginning of the study, skin strips were collected to measure basal levels of metals. Next, the volunteers did the first application of the creams and spent 6 hours in the city traffic. Then, skin stripping was performed to obtain new samples of the epidermis. Metals were extracted from skin strips and the following were analyzed by means of graphite furnace atomic absorption spectroscopy: Fe, Pb, Cr, Ni, and Zn. Variations in metal levels with respect to basal conditions were calculated. After exposure to pollution, all metals evaluated increased significantly. However, this was not observed in skin treated with the active cream, where there was a significant difference in metal levels compared to placebo (p<0.001).


• Antioxidant defense: After 15 and 30 days of product application and regular exposure of the volunteers to city pollution, skin samples were taken by means of tape stripping and analyzed. The antioxidant capacity of the skin was assessed by the ferric reducing antioxidant power (FRAP) method, while lipid peroxidation was determined by means of the MDA assay. The anti-pollution ingredient showed to improve the skin antioxidant pool by 23.5% (p<0.0001) and reduce lipid peroxidation by 24.7% (p<0.001) at the end of the treatment.

 
Adherence of Microparticles


The ability of the anti-pollution ingredient to remove microparticles from the skin surface was evaluated on 21 female volunteers (21-45 years old) who applied to the forearm skin a cream containing 5% cosmetic ingredient, while leaving another skin area untreated. After 20 minutes, microparticles modeling atmospheric pollution (1µm average size) were applied and then the skin was rinsed with water. The surface covered by the microparticles was visualized by videomicroscopy and measured.
 
An improvement of 20.2% (p<0.0001) in the removal of particles from the skin surface after rinsing was obtained with the anti-pollution ingredient and compared to non-treated skin. Such reduction in pollution adhesion to the skin suggests the potential capability of the cosmetic ingredient to obtain a cleaner and less dull skin complexion (Fig. 4).
 
 
Conclusions


The cosmetic ingredient Pollushield functional ingredient has been developed to help counteract the negative effects of the very present concern of pollution on the skin. The ingredient offers the complementary actions of a polymer able to bind to toxic metals and a strong antioxidant to assist in the reduction of oxidative damage. Several efficacy tests have been performed to reinforce its potential capacity of capturing contaminants such as metals, while maintaining cell viability despite the exposure to urban dust. This protection ability was also shown in skin explants by helping preserve the normal morphology and reducing peroxidation levels as well as certain markers of damage.
 
 
With a single application on volunteers exposed to outdoor pollution, it showed to induce a reduction of accumulated metals, while after continuous treatment it helped improve the skin opposition to oxidative stress. With one only application of the product, it also showed to improve protection against pollution particles from adhering to the skin for a less dull and better appearance. •
 

 
References

1. http://www.chinadaily.com.cn/china/2015-02/02/content_19466412.htm
 
2. air pollution. (2015). In Encyclopædia Britannica. Retrieved from http://www.britannica.com/science/air-pollution
 
3. Advanced Topics in Environmental Health and Air Pollution Case Studies. Chapter 6 Air Pollution, Reactive Oxygen Species (ROS), and Autonomic Nervous System Interactions Modulate Cardiac Oxidative Stress and Electrophysiological Changes by Elisa Ghelfi. InTech; 2011.
 
4. Basic Information about Disinfection Byproducts in Drinking Water: Total Trihalomethanes, Haloacetic Acids, Bromate, and Chlorite. In United States Environmental Protection Agency. Retrieved from http://www3.epa.gov/.
 
5. Sato M, Kondoh M. Recent studies on metallothionein: protection against toxicity of heavy metals and oxygen free radicals. Tohoku J Exp Med. 196(1):9-22, 2002.