New Delhi: As Delhi prepares for winter and another round of late fall smog, a study has revealed that the air within city homes contains fungal spores at levels 12 times above the WHO safety threshold, leading to skin allergies, respiratory problems, and increased anxiety among residents. Conducted by researchers from Delhi University’s Satyawati College, Jamia Millia Islamia, and South Dakota State University, the study also found bacterial levels to be ten times higher than WHO guidelines. Prolonged exposure to elevated fungal and bacterial concentrations renders indoor air in various areas of Delhi nearly as dangerous as the outdoor smog.
Published in Frontiers in Public Health, 2025, the study highlighted that most fungal particles measured smaller than 2.5 microns, allowing them to penetrate deep into the lungs and potentially cause lasting respiratory harm. A distinct seasonal trend was observed, with fungal levels increasing steadily from winter to their peak at approximately 6,050 CFU per cubic metre during the fall months of September to November, just prior to the onset of smog in Delhi. Bacterial levels surged from winter to summer, reaching their highest in August before decreasing in autumn.
Approximately 33% of residents experienced frequent headaches, 23% reported burning or irritated eyes, 22% suffered from persistent coughing and breathlessness, and 18% dealt with sneezing and allergic rhinitis, commonly referred to as hay fever. About 15% noted skin irritation and itching. The study indicated that children and young adults are particularly vulnerable, with 28% of children under 12 years and 25% of young adults aged 18 to 30 experiencing breathing difficulties, coughing, or allergy-related symptoms. The authors attributed this higher susceptibility to developing lungs, increased activity levels, and extended indoor exposure. Women reported significantly higher instances of eye and skin irritation, constituting nearly 60% of all dermatological and eye complaints, likely due to their longer indoor durations.
The investigation, titled “Microbial Indoor Air Quality Assessment and Health Correlations in Densely Populated Urban Areas of Delhi, India,” discovered that fungal and bacterial levels inside homes in densely populated regions of the national capital far exceeded the WHO’s safety standards, based on a year-long survey of households in North Delhi. Air samples were collected from 336 houses within the slum clusters of Ashok Vihar and Azadpur, which are characterized by low income, overcrowding, poor ventilation, and visible dampness. The survey examined all four seasons to monitor changes in microbial levels throughout the year.