Droplets. These droplets are usually pollen grains or dust spots (from a few microns to about 100 microns) . But for fine particles and toxic gases in the air (such as nitrogen dioxide, ozone and volatile organic compounds) , medical masks-even the best quality No fabric masks provide protection.

In order to completely cover the nose and chin, good masks are also wrinkled. They fit the face better than regular masks, but they don’t fit perfectly, such as when you have a beard. The doctor was trained to wear the mask 1 correctly, but the public did not. Air and pollutants enter the nose and mouth through the gap between the mask and the face.

Teaching people how to use masks is also very important. Any mask is uncomfortable to wear for a long time, 2 , especially on hot days, it is more difficult to breathe; carbon dioxide accumulation causes drowsiness 3 ; masks must be worn and taken off to talk and eat , Drink water; In addition, the filter may become wet, resulting in reduced performance. To save money, people sometimes wear a mask many times; once it is blocked, wearing a mask can be counterproductive.

Many outdoor workers are instructed and trained to use professional installations. These devices meet the standards set by the National Institute for Occupational Safety and Health. Simple cotton masks block dust and asbestos from construction sites and workshops; other masks contain active adsorbent materials that filter chemicals and gases more thoroughly; some respirators have waterproof masks and breathing valves. In other words, they are completely different from a square yarn.

Insufficient evidence

Medical masks have been fully studied in the clinical environment and have proven to be effective in preventing the spread of infectious diseases. But how effective they are against air pollution, we don’t know 4,5 . In fact, the function of any mask is difficult to quantify. There are many factors to consider, including particle size and source, type of mask, and face shape and behavior of the wearer.

An Indian child wears a mask on a hazy day. Image source: Sunil Ghosh / Hindistan Times / Getty

Some laboratories have researched the filtering function of mask materials. But only a few human experiments have tested the effect of wearing a mask in real situations. Most studies were done in Beijing, Shanghai, and the United States. Researchers usually only track for a few hours, and most focus on the effects on the heart. Few people have studied the effects on the respiratory system.

Some trends are mentioned in the report but are not statistically significant. For example, a study found that people who are accustomed to wearing a mask in a polluted environment have lower blood pressure and a more consistent heart rate than people without a mask. 6 Healthy adults wear masks more benefit than those with heart disease 6,7 . However, research has often diverged from direction and extent to time and response types.

The uneven level of pollution also makes it difficult to assess health effects. For example, in a busy intersection or road tunnel, the concentration of gas and ultrafine particles may be 100 times that of a remote alley. In addition, people’s age, gender, health status, medications, and activity styles make assessments complicated. Fitness and exercise people usually exercise more outdoors, increasing their exposure to polluted air. Men are more exposed to outdoor pollution, while women are more exposed to indoor pollution. There are no rigorous studies to quantify how people change their behavior when wearing a mask.


Next

People need to know when, why and how to wear a mask properly.

Experts and authorities need to gather evidence and make recommendations for situations where short-term wearing of a mask may be beneficial, such as during a sandstorm or in a heavily polluted city in a desert in Africa. Researchers should collect evidence on the effectiveness of masks against air pollution. Clinical trials should use larger sample sizes to track the long-term effects of high-risk populations.

WHO and other public health agencies should informext-remarks “> 5. Stockwell, R. E. et al. Am. J. Respir. Crit. Care Med. 198, 1339–1342 (2018).

6.Langrish, J. P. et al. Part. Fibre Toxicol. 6, 8 (2009).

7.Langrish, J. P. et al. Environ. Health Perspect. 120, 367–372 (2012).

8.Shi, J. et al. Environ. Health Perspect. 125, 175–180 (2017).

9.Laumbach, R. J. et al. Part. Fibre Toxicol. 11, 45 (2014).

The original article was published in the “Nature” review on October 01, 2019 under the title of Face masks could raise pollution risks

This article is from the WeChat public account: Nature Nature Research (ID: Nature-Research) , author: Wei Huang & Lidia Morawska