Having looked at some fairly hard hitting health topics in my last few pieces for the smog blog I thought this time I would look at a health issue that although causes significant concern and attention is perhaps only skin deep!

I have seen several pieces of research on the effects of air pollution on the skin over recent months and will attempt to summarize a couple of them in this article, but first I will try to summarize the effects of different types of pollution on skin health.

Air pollution and the skin

Our skin acts as shield against physical and chemical assaults on our bodies. The repetitive exposure to these factors can obviously have profound negative effects on the skin. Exposure of the skin to air pollutants has been associated with skin aging, inflammatory conditions for example eczema, psoriasis and atopic dermatitis, as well as skin cancer. (1) The major pollutants known to have negative effects on the skin include solar UV radiation, polycyclic aromatic hydrocarbons, volatile organic compounds, nitrogen oxides, particulate matter, ozone and cigarette smoke.

To complicate matters some air pollutants (ozone, nitrogen dioxide (NO2) and scattering particulates) can potentially have beneficial effects ion our skin health by blocking UV radiation; significant reductions in UV radiation has been observed in highly polluted areas. (I am not sure I want to swap a reduced risk of skin cancer from UV radiation for an atmosphere filled with other chemical and particulate pollutants).

The main article I will look at this time is “Traffic-related air pollution contributes to development of facial lentigenes: further epidemiological evidence from Caucasians and Asians. ” (2) This article was published in the Journal of Investigative Dermatology this year. Previous studies have linked air pollution with skin problems and aging. This study particularly concentrates on the effects of nitrogen dioxide (NO2) on the skin. As we know NO2 is a particular component of traffic pollution. The authors investigated the link between chronic exposure to NO2 and development of lentigo. Lentigo or lentigines are dark marks that develop on the skin as we age, often known as age spots or liver spots they tend to develop in areas of the skin that are exposed to the air.

My first thought about this study was why is it important to separate out the components of air pollution, surely it would be enough just to know that air pollution in general contributes to signs of skin aging. But then I thought about the implications for policy and control of pollutants. When policies are made limiting the allowable levels of certain chemicals this is obviously based on individual or small groups of associated chemicals, it is not based on generic nebulous terms such as “air pollution”. As such it is useful to have as much evidence of harm of individual components in order to strengthen the argument for tougher controls.

This study uses two populations; one Chinese and the other European, there have not been many studies looking at the effects of pollution on Asian skin, another reason why this study is interesting. Both populations were actually taken from other larger studies; this is quite common practice in clinical trials, saving time and resources by using individuals whose data has already been collected. The Asian group were Han Chinese from a large study in Taizhou (3). The European cohort was taken from another large study looking at the the influence of air pollution on lung function, inflammation and aging (SALIA) (4, 5). The two groups were broadly similar; all of the European group were women, as were 69% of the Chinese group. The exposure to smoking was similar with 20% of European group having been smokers and 21% of the Chinese group. The exposure to NO2 was also broadly similar at an average of 28.8ug/m3 in the European group and 24.06ug/m3 in Taizhou.

However there were also significant differences, the Chinese group included a much wider age range from 27 to 89 years with an average of 59 years, whereas the European group ranged from 66 to 79 years with an average of 73 years. In a study of this sort since the two groups are not being compared the differences do not matter, the study is looking to compare the effect of an external factor on the populations, however if the populations are too different there could be other confounding issues that might make the findings difficult to interpret. For example if the Chinese group did not include any older people then the numbers who had developed skin signs of aging would be very small and it might not be possible to derive any association or lack of association with exposure to air pollution.

Another potential issue is that the way NO2 levels were measured in the two groups were different, in Taizhou data was provided by the Taizhou Environmental Bureau, whereas in the SALIA study pollution exposure was estimated using land-use regression models developed in another study; European Study of Cohorts for Air Pollution Effects (ESCAPE) study (6). This would be a potential issue if the results for the different groups was very different, it then might not be clear where the differences were arising. Were differences due to differences between the way Asian and Caucasian skin responds to pollution or because the levels of pollution were not actually as similar as it appeared, or even is there actually some other factor causing the difference in skin appearance that has not been considered in this study. Additionally since the data in Taizhou was obtained from state monitoring stations, individual assignment of exposure was fairly coarse leading to small spatial variation.

How was skin compared?

Skin was visually assessed using a standardized photo reference scale and trained personnel in a highly standardized manner. The same group of personnel assessed both groups. The number of spots was counted then grouped and scored. Centrally defined variables including living conditions and sun exposure were taken into account. The same scale was used to evaluate the skin aging in both populations.

Findings

The score (number of age spots) was then compared to the NO2 exposure using linear regression models. Exposure to NO2 was significantly associated with more lentigenes on the cheeks in both cohorts, so an increase in NO2 of 10ug/m3 was associated with approximately 25% more lentigenes on the cheeks. However there was no association with the pollution levels and lentigenes on the back of the hands and forearms. The authors attributes this to a possible different pathogenesis (the way in which disease develops) in different anatomical areas. This seems a slightly implausible theory to me, there are differences in the skin in different parts of the body, for example the thickness and rapidity of cell turnover but the basic physiology of skin cells ought to be the same whether the cells are on the face or the forearms. However response to pollution could vary depending on location due to a combination with another factor for example exposure to sunlight, the cheeks are likely to have had more sun exposure than the arms.

The other question which occurred to me is how air pollution affects the skin? Does it cause aging effects externally, ie by sitting on and affecting the skin from the outside in a similar way to how sun exposure causes skin changes or is it via breathing in the pollution, absorbing harmful chemicals into the body and these having inflammatory effects, for example on the small blood vessels that supply the skin, or is it a combination of both. I suspect the latter. I could see that the inflammatory effects on blood vessels could explain the differences in appearance of lentigenes on the cheeks and the forearms, the cheeks are a notoriously vascular area of the skin, the reason we blush is because there are so many blood vessels near to the surface of the skin. So if lentigene formation was due to inflammatory changes to blood vessels in the skin the skin of the cheeks could be more susceptible and thus more closely associated with exposure to NO2.

Conclusions

The authors believe their study is of particular interest as it is the largest epidemiological study showing a link between traffic-related air pollution and lentigenes, the study also showed the association in both Caucasians and Asians.

Despite the differences in populations and methods of measuring NO2 the authors conclude that the similar effect estimates in both studies indicate a true underlying effect. The authors also tried to evaluate whether NO2 or PM10 were more likely cause of the development of lentigene. They concluded that the effects of PM 10 and NO2 cannot really be disentangled as they are so closely associated with each other.

I will now briefly consider another article relating to the effects of air pollution on skin health. “Olay reveals new insights on the clear and present danger of air pollution on skin health” (7). This article was sponsored by the skincare brand Olay. I have reviewed the information presented in the study carefully, and as far as I can tell the methodology etc is robust. However we do of course need to remain objective and mindful that any industry sponsored research is only likely to be published if it supports the sponsor’s agenda. So in this case since Olay are trying to sell products which counteract the effects of pollution on the skin we must remember that if the research had shown no benefits of their products or no negative effects of pollution to be countered by their products the research may not have been published.

In this study Olay, alongside external dermatologists evaluated the impact of air pollution on skin health. The study was conducted across Beijing, taking in areas of higher and lower pollution. They measured multiple aspects of skin health and appearance on over 200 women while recording lifestyle and skincare routines. They found that those living in the more polluted areas had worse skin hydration than those living in cleaner suburbs. This finding was despite some evidence of better lifestyle choices (such as cleansing routines, water consumption and greater skin care product usage). In addition lower levels of important biomarkers indicating compromised skin barrier function were found in the subjects from more highly polluted areas..

In addition to looking at skin hydration this study also found a relationship between air quality and skin conditions. There was a correlation between when spikes in air pollution were measured and the numbers of subjects suffering from skin problems such as urticaria (hives).

Summary

So in summary air pollution is bad news for your skin health, living in a more polluted environment is likely to increase the signs of skin aging such as wrinkles and age spots. These effects are likely to be compounded by other skin damaging activities such as sun exposure (even if the pollutants can block some of the damaging UV rays) and smoking. If you live in a polluted area it would be advisable to take the best care of your skin that you can and reduce your exposure to the pollution as much as possible.

Terms

Lentigo/ Lentigenes — patches of darker pigmentation on skin, commonly known as age or live spots.

linear regression models — Linear regression is the most basic and commonly used predictive analysis. Regression estimates are used to describe data and to explain the relationship between one dependent variable and one or more independent variables.

References

1. Drakaki E, Dessinioti C, Antoniou C. Air pollution and the skin. Front. Environ. Sci., 2014. Accessed via URL: http://dx.doi.org/10.3389/fenvs.2014.00011. Accessed 16th April 2016.

2. Traffic-related air pollution contributes to development of facial lentigenes: further epidemiological evidence from Caucasians and Asians. J. Invest. Dermatol 2016. Doi:10.1016/j.jid.2015.12.045

3.Wang X, Lu M, Qian J et al. Rationales, design and recruitment of the Taizhou Longitudinal Study. BMC Public Health 2009;9:223.

4. Schikowski T, Ranft U, Sugiri D et al. Decline in air pollution and prevalence in respiratory symptoms and chronic obstructive pulmonary disease in elderly women. Respir Res 2010: 11:113.

5. Vossoughi M, Schikowski T, Vierkotter A et al. Air pollution and subclinical airway inflammation in the SALIA cohort study. Immun Aging 2014; 11:5.

6. Beelan R, Hoek G, Vienneau et al. Development of NO2 and NOx land use regression models for estimating air pollution exposure in 36 areas in Europe — The ESCAPE project. Atmos Environ 2013; 72 (2):10-23.

7. P&G News. Olay reveals new insights on the clear and present danger of air pollution on skin health. 2014. Accessed via URL: http://news.pg.com/press-release/pg-corporate-announcements/olay-reveals-new-insights-clear-and-present-danger-air-poll. Accessed 8th April 2016.