High-Efficiency Particulate Air (HEPA) filtration can substantially reduce airborne particulate matter indoors. Research has also investigated whether reducing indoor particle exposure can produce measurable benefits to cardiovascular health.

One study conducted in Denmark examined 21 nonsmoking couples between the ages of 60 and 75 in their homes. The randomized, double-blind crossover study exposed participants to particle-filtered air during one 48-hour period and nonfiltered air during another 48-hour period. The researchers measured indoor particulate concentrations and assessed several health indicators, with microvascular function as the primary outcome.

The researchers found that filtration substantially reduced exposure to indoor particles. More importantly, microvascular function improved by 8.1% (95% confidence interval, 0.4%–16.3%) during the filtration period. Microvascular function was assessed by measuring changes in peripheral arterial tone following temporary restriction of blood flow to the arm.

The findings are consistent with other research showing that exposure to particulate matter can affect vascular function and that reducing indoor particulate exposure may have measurable physiological benefits. However, this study was small and lasted only 48 hours. It measured a marker of vascular function rather than cardiovascular disease or cardiovascular events. In addition, the researchers did not find statistically significant changes in the secondary biomarkers of inflammation and oxidative stress after correcting for multiple comparisons. The results should therefore be viewed as evidence of a possible short-term cardiovascular benefit of reducing particle exposure, rather than proof that HEPA filtration prevents cardiovascular disease.

Subsequent research has produced additional evidence that indoor air filtration can affect cardiovascular measures, although results have not been completely consistent across studies and populations. A later study of adults exposed to traffic-related and wood-smoke particulate matter, for example, found that previous research had observed improvements in vascular function following HEPA filtration, while its own results did not demonstrate the same relationship in all participants. This illustrates why individual intervention studies should not be interpreted as establishing a universal clinical benefit.

The broader evidence linking fine particulate matter to cardiovascular health is nevertheless substantial. PM2.5 can penetrate deeply into the respiratory system, and exposure has been associated with cardiovascular and respiratory disease. Reducing exposure to particulate matter is therefore an important part of improving indoor air quality.

It is important to remember that HEPA filtration removes particles; it does not remove every type of air pollutant. HEPA filters are designed primarily to capture airborne particulate matter. Gaseous pollutants and volatile organic compounds generally require different technologies, such as appropriately designed sorbent filtration, while eliminating or reducing the source of pollution and providing appropriate ventilation remain important components of indoor-air-quality management.

Understanding Particle Size

Particle sizes are commonly expressed in micrometers (µm), where one micrometer is one-millionth of a metre. PM10 refers generally to particles 10 µm or smaller in aerodynamic diameter, while PM2.5 refers to fine particles 2.5 µm or smaller. PM2.5 is too small to be seen individually by the naked eye. For comparison, a typical human hair is approximately 50–70 µm in diameter, although the diameter of individual hairs varies considerably.

These size comparisons help illustrate why fine particles can remain suspended in the air and penetrate much deeper into the respiratory system than larger particles. They also demonstrate why an effective mechanical air filter must be capable of capturing particles that are much smaller than those visible as ordinary household dust.

By Michael Chiu, MWS, CI
Previously published in Ming Pao Daily News – Updated and Revised in 2026