The Invisible Life Around Us: Bioaerosols in Indoor Air

Even a clean, closed room holds tiny particles of biological origin: bacteria, fungal spores, pollen and fragments. Here is what they are, where they come from and how to keep them in check.

By Kashish Sharma, M.Sc. Student, School of Environmental Sciences, Jawaharlal Nehru University, India · 31 Oct 2026 · 3 min read

Indoor bioaerosols can be living (viable) or dead and fragmented (non-viable), and come from people, pets, damp surfaces and ventilation systems.

Have you ever wondered what is in the air around us, even inside a perfectly clean room? Beyond visible dust, indoor air contains microscopic biological particles called bioaerosols. These include bacteria, viruses, fungal spores, pollen and microbial fragments. Although many are harmless, some can affect human health and indoor air quality.

Is the air around us really clean?

Imagine sitting in a classroom, library or bedroom. The surroundings look clean, the windows are closed and everything seems normal. But the air around you may hold thousands of microscopic biological particles that cannot be seen with the naked eye.

This invisible biological world is an important part of our indoor environment. We often link air pollution with vehicle exhaust, industrial smoke and outdoor dust. However, indoor air can also contain biological contaminants that come from people, animals, plants, building materials and the surrounding environment. These airborne biological particles are together known as bioaerosols.

Recent research, including a 2026 review published in Atmospheric Environment, highlights the need to study the characteristics of bioaerosols, their health risks, the techniques used to sample them and the challenges in analysing them.

Common types of bioaerosols: viruses, bacteria, mould spores, pollen and skin cells — Figure 1. Common types of indoor bioaerosols. Image: WellAir (wellairsolutions.com), used for illustration; all rights with the original owner.

What are bioaerosols?

Bioaerosols are tiny airborne particles of biological origin. They can be whole microorganisms, fragments of organisms or substances produced by living things. They are broadly classified into two groups:

Viable bioaerosols are living microorganisms, such as bacteria and fungi, that can stay biologically active under suitable conditions. Infectious viruses are also studied as bioaerosols, although they need host cells to multiply.
Non-viable bioaerosols include dead microbial cells, pollen, biological fragments, endotoxins and other substances of biological origin.

Characteristics and sources

The size of a bioaerosol particle controls how long it stays suspended in the air, how far it travels and where it settles in our respiratory tract when we breathe it in.

Major indoor sources include breathing, coughing and sneezing, pets, carpets, damp building materials and ventilation systems. Biological particles from outdoors also enter buildings through windows and air exchange. Moisture build-up, in particular, encourages the growth of fungi (mould).

Health effects

How indoor bioaerosols are released, carried, deposited and inhaled, and the health responses they can cause — Figure 2. Exposure to indoor bioaerosols and the body’s response. Image: graphical abstract of Naik, A. K. and Zabłocka-Godlewska, E. (2026), Atmospheric Environment, 373, 121934 (Elsevier, via ScienceDirect); reproduced for illustration, all rights with the publisher.

Exposure to certain bioaerosols is linked to allergic rhinitis, worsening of asthma, irritation of the airways and infections. Microbial components such as endotoxins (from bacterial cell walls) and β-glucans (from fungal cell walls) can trigger inflammation.

Health effects depend on which microbes are present, how concentrated they are, how long a person is exposed and how sensitive that person is. Children, older adults and people with weak immunity may face greater risks from some biological agents.

Challenges and control measures

Monitoring bioaerosols is not easy. Samplers differ in how efficiently they collect particles, microbes can lose viability during sampling, conditions keep changing, and there are no universal health-based exposure limits. Helpful preventive steps include good ventilation, HEPA filtration, moisture control, regular cleaning and proper maintenance of air-conditioning (HVAC) systems.

The air we cannot see matters

Indoor bioaerosols affect both the quality of our indoor environment and our respiratory health. Understanding their sources, biological characteristics, sampling methods and health effects is essential for assessing exposure properly. Standardised monitoring methods and better indoor air management can help reduce the possible health risks.

A room may look spotless, but its air tells a much deeper story. Understanding that invisible story is the first step towards healthier indoor spaces.

References and further readings

Naik, A. K. and Zabłocka-Godlewska, E. (2026). Bioaerosols in indoor environments: characteristic, health risk, sampling, analysis methodologies and challenges – a review. Atmospheric Environment, 373, 121934.
World Health Organization (2009). WHO Guidelines for Indoor Air Quality: Dampness and Mould. WHO Regional Office for Europe, Copenhagen.
Srikanth, P., Sudharsanam, S. and Steinberg, R. (2008). Bio-aerosols in indoor environment: composition, health effects and analysis. Indian Journal of Medical Microbiology, 26(4), 302–312.
United States Environmental Protection Agency. Care for Your Air: A Guide to Indoor Air Quality.
WellAir. Bioaerosols explained: what they are, where they come from, and why they matter for IAQ. wellairsolutions.com (source of Figure 1).