Despite being a common sight in polluted cities, particularly those in Asia, new research suggests that face masks designed to filter out pollution particles may not be as effective as they claim to be.

Carried out by an international team of researchers from Heriot-Watt and the Institute of Occupational Medicine in the U.K., the study assessed the effectiveness of a selection of masks in Beijing.

With estimates suggesting that air pollution causes 1.6 million premature deaths in China each year, the researchers also looked at the levels of air pollution in the capital and the potential effects on health.

The team purchased nine masks to test. All nine claimed that they would protect wearers from inhaling fine particle pollution, which primarily comes from vehicle exhausts as well as fuel combustion and power plants. Also known as PM2.5, fine particulate matter are tiny particles suspended in the air measuring 2.5 micrometers or smaller, which, when inhaled, are deposited in the lungs. By comparison, a human hair is between 50 and 70 micrometers thick.

The team first tested how effective each mask was at filtering pollution particles by drawing airborne diesel exhaust through a section of the mask's material for 30 minutes and measuring the levels of particulate matter and black carbon on both sides.

The masks were then tested on 10 volunteers who were exposed to diesel exhaust in a lab while performing everyday tasks such as talking, sitting, bending over and walking.

The results showed that the masks varied significantly in their effectiveness, with the team finding that depending on the material used for the mask the average particle and carbon penetration ranged from 0.26 per cent to 29 per cent.

The tests on the volunteers revealed even greater difference, with the team finding that the average leakage from the masks ranged from as low as three percent to as much as 68 percent while the participants performed sedentary tasks such as sitting.

While performing active tasks the average leakage ranged from seven percent to 66 percent.

"Only one mask had an average leakage below 10 per cent on both active and sedentary tests," added lead researcher John Professor Cherrie.

Although retail masks must be certified to local or international standards the results suggest that the face masks currently found on the market may not provide adequate protection.

Although little information is available on which product will offer the best protection, Professor Cherrie offers some advice. "If it's important for you to protect yourself or your family with masks, choose the best one you can and look for one marketed to workplaces. Don't opt for the cheapest option, choose the one that's most likely to do the best job."

The results can be found published online in the journal Occupational and Environmental Medicine.