Asthma, HEPA and PM2.5

Asthma is not one single disease. It is a chronic inflammatory airway condition with different subtypes, including Type 2 eosinophilic asthma and non eosinophilic asthma. While the biology differs, both types are strongly affected by environmental exposures, especially the air we breathe every day.

One of the most important triggers is fine air pollution known as PM2.5. These particles are small enough to travel deep into the lungs and reach the small airways, where asthma inflammation often causes symptoms and flare ups. Because of their size, PM2.5 particles are not easily filtered by the nose or upper airways.

PM2.5 comes from many everyday sources. The biggest contributor is traffic, not just from exhaust fumes but also from tyre and brake wear, which creates pollution even in areas that do not feel busy. Other common sources include wood burners, waste and biomass burning, industrial activity, cooking fumes, and dust from roads or soil. Indoors, PM2.5 can rise quickly during cooking, especially in homes with poor ventilation.

Some PM2.5 is formed in the air rather than released directly. Gases from vehicles, heating, farming, and industry can react in the atmosphere and turn into fine particles. These particles can travel long distances and enter homes even when windows are closed. Pollution levels also change with the seasons, often increasing in winter due to heating and in summer due to sunlight driven chemical reactions.

This matters for asthma because PM2.5 irritates the airways and increases inflammation. The smallest airways are affected the most. Studies show that reducing PM2.5 exposure improves small airway function and reduces airway inflammation, even when traditional lung function results do not change.

HEPA air filters are designed to remove very small particles from the air, including PM2.5. Portable HEPA filters can reduce indoor PM2.5 levels by a meaningful amount and are recommended by allergy and asthma organisations as part of environmental control when pollution sources cannot be fully removed. By lowering particle exposure, HEPA filters may reduce airway irritation and support better breathing control.

Importantly, research shows benefits in both eosinophilic and non eosinophilic asthma. In some studies, people without high eosinophilic inflammation showed particularly clear improvements in small airway function. This highlights that cleaner air matters across asthma types, not just in allergic disease.

HEPA filters are not a replacement for inhalers or medical care but improving indoor air quality is a simple idea with meaningful physiological effects when used alongside guideline directed asthma treatment.

Have you used a HEPA air filter and noticed an improvement in your asthma symptoms? And if so, which device worked for you?