Urban living can have lasting effects on the health of skin and it is not just ultraviolet (UV) light that can wreak havoc on the body's first line of defence.
Other pollutants, toxins and chemicals in the urban environment, along with the impact of urban lifestyle, such as increased stress, can all affect the skin, a recent study comparing rural and urban Beijing residents showed.
Chronic exposure to these pollutants led ultimately to tissue damage, according to the study of 206 women aged between 30 and 45 who had lived in the rural (Mi Yun) and urban (Shi Jing Shan) areas for at least 10 years.
It found the urban residents tended to sleep longer, drink more water, wash off make-up nightly and use skincare products more often. Yet, they had poorer skin hydration than those living in the rural areas.
Rural residents showed higher photodamage - including fine lines, wrinkles and pigmentation - but better skin hydration, as their skin was less dry and dull.
The results of the study, presented at several academic conferences, were shared at the Singapore International Conference on Skin Research last week.
Such research could be vital as more people flock to live in cities.
Right now, more than half the world's population is urban and this proportion is expected to grow.
"It's still early days but the study tells us there's something else besides UV that may be impacting skin," said Dr John Oblong, principal scientist at Procter & Gamble, which funded the study. He presented the study and was a panellist at the conference discussion.
"Urban living is beyond what the environment is. There's stress, maybe that could be one factor."
Also, besides the known vehiclular and industrial pollutants, there could be others that people are not aware of, said Associate Professor Paul Bigliardi, a senior principal investigator at A*Star's Institute of Medical Biology, another panellist at the discussion.
For instance, some buildings are using more and more fragrances to overcome unpleasant odours, he said. These fragrances are modern pollutants that we do not even think about.
Some dermatologists outside of the conference agree that pollutants from the urban environment may have a detrimental effect on the skin. "External pollutants initiate oxidative stress, which can damage the skin barrier," Dr Derrick Aw, head and senior consultant (dermatology) at National University Hospital, told Mind & Body.
Oxidative stress is an imbalance between the production of free radicals and the body's ability to counteract the harmful effects of these molecules. In urban cities, it is not just the outdoors that has air pollutants; there are also indoor air pollutants which can come from tobacco smoke, stoves, furniture, animal dander, mould spores and bacteria, Dr Aw added.
Dr Tan Kian Teo of Skin Physicians at Mount Elizabeth Medical Centre told Mind & Body that the main environmental factors that damage skin in general are ultraviolet light, cigarette smoke and ambient ozone.
Ambient ozone air pollution at ground level is an important component of smog, he said.
Another adverse factor is smoke haze from forest fires, which affects people in any environment, urban or rural.
Indeed, studies have shown that haze can contribute to the premature ageing of skin and exacerbate inflammatory skin conditions such as eczema and acne, Dr Stephanie Ho, a consultant dermatologist with her own practice at Pacific Plaza, said.
The sun, smoking and haze can also hasten the formation of wrinkles and lead to premature ageing, she said.
For those with skin conditions like eczema, the effect of urban living on their skin can be more pronounced. Certain pollutants may even trigger the condition.
Many clinical studies have linked the exposure to air pollutants to the development and aggravation of eczema, a common, chronic itchy skin condition that usually begins in childhood, said Dr Aw.
"For example, international studies demonstrated that babies who are exposed just before and just after birth to environmental tobacco smoke, volatile organic compounds and particulate matter could more likely develop eczema," he said.
But many things remain unknown, such as the exact hazardous element in the various urban pollutants, the amount of exposure to air pollutants that will cause clinically significant abnormalities in the skin and who will be more susceptible to such influences, Dr Aw added.
To counteract the effects of these environmental pollutants, use sun screen and topical formulations with antioxidants such as vitamins C and E, niacinamide and reservatrol, said Dr Tan.