Aeroallergens: Nepal’s Ignored Biological Threat

With an Air Quality Index (AQI) of 217 on April 23, 2026, Kathmandu once again ranked among the world’s most polluted cities, surpassing Lahore, Dhaka, and Delhi. As summer approaches, Nepal once again braces itself for rising temperatures, wildfire smoke, and choking haze in the capital and around the nation. Public discussions on air pollution tend to focus on particulate matter, vehicle emissions, brick kilns, and construction dust. However, there's an important dimension that remains overlooked: biological pollutants. Nepal’s air pollution crisis is genuine, substantiated, and of alarm severity level. According to the Health Effects Institute’s State of Global Air 2025 report, air pollution accounted for over 40,000 deaths in Nepal in 2023, corroborating the most acute public health emergencies in South Asia. However, aeroallergens, key biological constituents of air pollution, remain unmonitored and untouched by national health policy, a critical gap in addressing national health security.

Nepal’s air is constantly contaminated with fungal aeroallergens, which are microscopic spores generated by mold, although the issue is often neglected. A 2019 study found fungal spores were highest in Kathmandu during autumn, summer, and spring simultaneously, where Aspergillus, Penicillium, Cladosporium and Alternaria species were the most predominant among others. These species thrive in Nepal’s warm, humid environments from the mid-hills to the agricultural plains in the Tarai. These spores are not just irritants; they can be potentially lethal for immunocompromised individuals, those living with HIV, undergoing chemotherapy, long-term corticosteroid therapy, or managing uncontrolled diabetes.

Airborne fungi

Another 2021 Tribhuvan University Journal of Microbiology identified Penicillium and Cladosporium as the most prevalent airborne fungi, with Aspergillus showing reduced sensitivity to first-generation azoles in Kathmandu. The Infectious Diseases Society of America confirms that exposure to airborne Aspergillus spores is the primary route of severe fetal fungal infection in vulnerable patients. Beyond infection, fungal exposure contributes to severe asthma with fungal sensitisation and allergic bronchopulmonary aspergillosis, conditions often misdiagnosed in resource-limited settings. In a country still grappling with tuberculosis, where thousands of patients are immunocompromised, this intersection of airborne fungi and weakened immunity is a public health concern Nepal is not yet prepared to address.

Another ignored biological pollutant is pollen, airborne plant particles released during reproductive cycles. In Nepal, altitude gradients that produce remarkably diverse vegetation create a long, poorly characterised pollen season. At high concentrations, it behaves like a pollutant, triggering allergic rhinitis, conjunctivitis, and asthma, and interacts synergistically with chemical pollutants such as diesel particulates to amplify immune responses beyond what either agent causes alone. Invasive species play a vital role in exacerbating spore air pollution by forming dense monocultures, releasing massive quantities of allergenic pollen or spores, and altering ecosystems to facilitate further dispersal. Parthenium hysterophorus (Pati Jhar), a prominent invasive species, causes severe allergic reactions like asthma, skin rashes, puffy eyes, peeling skin, and eczema.

Climate change is intensifying this threat. The Lancet Planetary Health 2019 study shows that rising temperatures are extending allergenic pollen seasons and increasing airborne pollen loads from the last 20 years. The mechanism is two-fold: warmer temperatures accelerate plant metabolism, causing earlier and more prolonged flowering, while simultaneously reducing air density in ways that keep lighter biological particles, such as spores and pollen, aloft for longer periods and across greater distances. In Nepal, records from 1971-2014 reveal that maximum annual temperatures have risen by 0.056°C per year, already putting these dynamics in motion. This results in a longer, more severe biological pollution season affecting communities, with no warning system to alert them.

Nepal does not need to start from scratch. Several countries have already recognised biological pollutants as a legitimate component of air quality reporting. The European Aeroallergen Network (EAN) operates a continent-wide network of pollen monitoring stations and publishes real-time pollen concentration forecasts integrated into national health advisories across Finland, Germany, Austria, and the United Kingdom. The UK Meteorological Office issues daily pollen forecasts categorised as low, moderate, high, and very high, much like AQI reporting. South Korea’s Korea Meteorological Administration operates a color-coded pollen alert system during allergy seasons. These are not academic add-ons; they help hospitals anticipate asthma surges, enable vulnerable populations to reduce exposure, and guide clinicians toward more accurate, environmentally informed diagnoses.

Policy blind spot

Despite clear scientific evidence, Nepal’s health system is not equipped to monitor biological pollution. There is no national aerobiology monitoring programme, and the Department of Environment’s AQI monitoring network tracks chemical pollutants while ignoring biological ones. Essential infrastructure, like volumetric spore traps, microscopy expertise, and mycological culture capacity, is entirely lacking in the health system. Deficit of trained aerobiologists and allergists further compromises diagnosis, with many cases misclassified as generic respiratory infections. Ultimately, Nepal’s health policy remains reactive, focusing on visible threats while invisible risks continue to escalate.

Nepal should, first, pilot a network of volumetric allergenic pollen and fungal spore monitoring stations in ecologically representative zones, the Kathmandu Valley, the Tarai lowlands, and at least one mid-hill site. Second, integrate fungal aeroallergen data into the existing Department of Environment AQI dashboard, even in a preliminary form, to bring this invisible risk into public view. Third, urban planning and green-space management should identify and remove invasive species and allergenic plant species. Fourth, task the Nepal Health Research Council (NHRC) with a national study on sensitisation to key allergens like Aspergillus, Alternaria, and dominant local pollen species, generating the indigenous evidence that currently does not exist. Finally, partner with networks such as EAN to leverage existing monitoring protocols and training.

Nepal’s air carries more than dust and diesel. It contains aeroallergens whose health impacts go unexamined because they go unmonitored. Recognising this gap is the first step; delaying it only exacerbates a crisis already borne most heavily by the vulnerable.

(Dulal is a scientist at the Nexus Institute of Research & Innovation (NIRI), and Pokhrel is a research assistant at the NIRI.)