Fine particulate matter known as PM2.5, including particles commonly found in haze and polluted air, may be associated with a higher risk of death by suicide, suicide attempts and suicidal thoughts, according to a systematic review and meta-analysis published in the Journal of Epidemiology & Community Health.
The findings point to a possible connection between polluted air and suicide-related outcomes. They do not prove that haze or PM2.5 directly causes suicidal behaviour. Most of the studies reviewed were observational, meaning they identified associations rather than establishing cause and effect.
“The pooled analysis showed statistically significant associations between short-term exposure to PM2.5 and PM10 and suicide-related outcomes. It also identified associations involving long-term exposure to PM2.5 and NO₂”
The researchers say environmental exposures should nevertheless receive greater attention in suicide prevention strategies. Air quality is already recognised as a major factor in respiratory and cardiovascular health. The new findings suggest that its possible relationship with mental health also warrants further investigation.
PM2.5 refers to particles measuring 2.5 micrometres or less in diameter. These particles are among the pollutants that can contribute to haze. They may come from wildfires, peat fires, agricultural burning, vehicle exhaust, industrial activity and other combustion sources.
During haze episode, PM2.5 concentrations can rise sharply. Smoke and other pollutants may remain suspended in the atmosphere, reducing visibility and affecting large populations. In some regions, haze can travel across borders, exposing people far from the original source of the fires or emissions.
The review also examined PM10, a larger category of particulate matter, and nitrogen dioxide, or NO₂. PM10 can also be present in polluted air and haze. NO₂ is produced mainly by combustion from road traffic, industrial activity, power generation and heating systems.
The research was conducted against the background of a continuing global suicide crisis. More than 720,000 people die by suicide worldwide each year, according to the World Health Organization. The organisation aims to reduce the global suicide rate by one-third between 2013 and 2030.
Researchers describe suicide as a complex public health issue. Mental illness, physical health, trauma, social isolation, financial hardship, biological vulnerability and access to care can all influence risk. Environmental conditions may interact with these factors rather than acting independently.
To assess the available evidence, scientists searched research databases for relevant studies published in English between January 2010 and April 2024. Of 287 studies selected for full-text review, 45 met the eligibility criteria.
Thirty-three studies examined death by suicide. Seven investigated suicidal thoughts, while five focused on attempted suicide. Most studies assessed air pollution. Thirty-eight considered air pollutants, three examined water pollution, three assessed noise pollution and one looked at light pollution.
The researchers combined the results of 29 studies in a pooled statistical analysis. They assessed the remaining 16 studies through a narrative review, which summarised the evidence without statistically combining the findings.
The pooled analysis showed statistically significant associations between short-term exposure to PM2.5 and PM10 and suicide-related outcomes. It also identified associations involving long-term exposure to PM2.5 and NO₂.
The outcomes included death by suicide, attempted suicide and suicidal thoughts. The results therefore suggest that both immediate changes in air pollution and more sustained exposure may be relevant. However, the studies used different methods, populations and exposure measurements, limiting the certainty of the conclusions.
PM2.5 is a particular concern because its particles are small enough to travel deep into the lungs. Some may pass into the bloodstream. Researchers suggest that exposure could contribute to inflammation, oxidative stress and changes in nervous system function.
These processes might affect brain systems involved in mood, emotional regulation and the response to stress. Air pollution may also worsen sleep, increase physical discomfort and reduce the ability to exercise outdoors. Such effects could place additional strain on people already experiencing depression, anxiety, trauma or chronic illness.
The review does not show that haze causes suicidal behaviour in people exposed to it. It also cannot determine whether a specific haze event contributed to an individual death or suicide attempt. Its findings indicate an association at population level, looking at the particulates found in polluted air.
The researchers identified possible associations involving other air pollutants, including sulphur dioxide and ozone. The narrative review also suggested a potential relationship between noise pollution and suicide-related outcomes. These findings were less conclusive than those concerning PM2.5, PM10 and NO₂.
Noise may affect mental health by disrupting sleep and increasing stress. Traffic, aircraft, railway and industrial noise can be persistent, particularly in urban areas. The review does not establish a direct pathway from noise exposure to suicidal behaviour.
Evidence regarding water and light pollution was limited. The researchers could not conduct pooled analyses for either exposure because too few studies were available and the outcomes varied. Findings from the narrative review were inconsistent.
Some substances that can contaminate water, including arsenic, lead, lithium and nitrate, have previously been linked to neurological effects. The current review does not provide enough evidence to determine whether water pollution affects the risk of suicide.
The researchers also examined sociodemographic factors, including sex and income. They found no clear associations between these factors and death by suicide or suicidal behaviour within the studies included in the review. This finding should be interpreted cautiously, since social and economic circumstances can influence health, living conditions and access to support.
Several limitations affect the strength of the evidence. The number of studies examining each outcome was relatively small. The studies differed in design, pollution measurements, exposure periods, participant characteristics and definitions of suicidal behaviour.
Many researchers estimated pollution exposure from a person’s residential location. This may not reflect the air breathed at work, school or other places. It may also fail to capture differences between outdoor and indoor environments.
Measuring exposure during haze can be especially difficult. Pollution levels may vary between neighbourhoods and change according to wind, rainfall, temperature and the intensity of burning. Building ventilation, air filtration and time spent outdoors may also influence individual exposure.
The studies may have been affected by confounding factors. Poverty, poor housing, urban density, occupational stress, access to healthcare and availability of green space may be linked both to pollution exposure and to suicide risk.
Publication bias is another possible limitation. Studies reporting an association may be more likely to be published than those finding no relationship.
Despite these uncertainties, the review adds to research linking air pollution with depression, anxiety, cognitive decline and other neurological outcomes. It extends that work by considering suicidal thoughts, suicide attempts and deaths by suicide.
The findings may have implications for public health responses during haze episodes. Authorities already advise residents to monitor air quality, reduce strenuous outdoor activity and limit exposure when particle levels are high. These measures are particularly important for people with respiratory or cardiovascular conditions.
If future research confirms a relationship with suicide risk, haze preparedness may also need to include mental health considerations. Clear public communication, access to healthcare and support for vulnerable people could become part of a wider response.
Long-term measures could include reducing vehicle emissions, improving industrial controls, expanding clean public transport, preventing agricultural and peat fires and strengthening cooperation between regions affected by transboundary haze.
The researchers call for collaboration between environmental health specialists, mental health professionals, policymakers and urban planners. They also recommend further research using more precise exposure measurements and detailed information about clinical, social and environmental conditions.
The findings should not be interpreted as meaning that haze will cause someone to become suicidal. Suicide is complex, and no single pollutant explains an individual’s thoughts or actions.
Anyone experiencing suicidal thoughts should seek immediate help from local emergency services, a crisis service or a trusted healthcare professional. Support should be sought regardless of air-quality conditions.
The review’s main message is that environmental exposures may be modifiable risk factors. Reducing PM2.5 and other pollutants could benefit the lungs and heart while potentially supporting wider mental wellbeing.
For now, the evidence points to a meaningful association between exposure to PM2.5, PM10 and NO₂ and suicide-related outcomes. It does not establish that PM2.5 particles found in haze directly cause suicide. It does show why the possible mental health effects of polluted air deserve closer scientific and public health attention.
If you are lonely, distressed, or having negative thoughts, Befrienders offers free and confidential support 24 hours a day. A full list of Befrienders contact numbers and state operating hours is available here: www.befrienders.org.my/centre-in-malaysia. There are also free hotlines for young people: Talian Kasih at 15999 (24/7); Talian BuddyBear at 1800-18-2327(BEAR)(daily 12pm-12am); Mental Health Psychosocial Support Service (03-2935 9935 or 014-322 3392); and Jakim’s Family, Social and Community Care Centre (WhatsApp 0111-959 8214).
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