In the previous episode, we discussed air pollution and lung cancer in non-smokers. The other day, an elderly gentleman visited my clinic with worsening breathlessness. He had never smoked, rarely travelled, and spent most of his time indoors.
“Doctor,” he asked, “if I stay at home all day, how can pollution affect me?” His question reflects a common misconception. When we think of air pollution, we imagine traffic congestion, industrial emissions, and crowded city roads. Rarely do we think about the air inside our own homes. Yet according to the World Health Organization (WHO, 2024), people spend nearly 90 percent of their time indoors, making indoor air quality a major determinant of health.
The air inside our homes: Unlike outdoor pollution, which is often visible and widely discussed, indoor pollution often goes unnoticed. It arises from everyday activities and sources that are part of our routine lives, cooking, especially cooking with wood, buffalo cow dung cakes, tobacco smoke, incense sticks, mosquito coils, cleaning products, paints, furniture materials, and poor ventilation. Many of these pollutants are invisible. There is no dramatic cloud of smoke or unpleasant smell to alert us.
Yet harmful particles and gases may gradually accumulate within enclosed spaces. A report from the United States Environmental Protection Agency (EPA, 2023) noted that indoor pollutant levels can sometimes be two to five times higher than outdoor concentrations, particularly in poorly ventilated buildings. Modern homes are increasingly designed to conserve livability by reducing air exchange with the outside environment. While this improves efficiency, it may also trap pollutants indoors for prolonged periods. Children, older adults, pregnant women, and individuals with chronic respiratory or cardiovascular diseases are particularly vulnerable. Because they spend a large proportion of their time indoors, even modest increases in pollutant exposure may have significant health consequences.
The smoke: Among indoor pollutants, tobacco smoke remains one of the most dangerous. Many smokers believe that smoking near an open window, on a balcony, or in a separate room adequately protects other family members. Unfortunately, scientific evidence suggests otherwise. According to the U.S. Surgeon General’s Report on The Health Consequences of Involuntary Exposure to Tobacco Smoke (2006), secondhand smoke causes lung cancer, coronary artery disease, heart attacks, and respiratory illness in non-smokers. The report concluded that there is no risk-free level of exposure. Children are particularly vulnerable.
According to the Centre for Disease Control and Prevention (CDC, 2024), children exposed to secondhand smoke experience higher rates of asthma attacks, respiratory infections, ear infections, and impaired lung growth. The danger does not disappear when the cigarette is extinguished. A study by Matt and colleagues published in the journal Tobacco Control in 2011 described the phenomenon of “third hand smoke.” Toxic residues from tobacco smoke settle on walls, curtains, carpets, furniture, and clothing, where they may persist for weeks or even months. Young children are especially susceptible because they frequently touch contaminated surfaces and place their hands in their mouths.
For many families, this information comes as a surprise. They may avoid smoking directly in front of children while unknowingly exposing them to harmful pollutants that remain in the home environment long afterward. The consequences of passive smoking often extend far beyond the smoker. In many households, a husband who smokes may unknowingly expose his wife to tobacco smoke for years, while children and elderly parents share the same environment. Unlike active smokers, these family members have no choice in the exposure. Studies have shown that long-term passive smoking increases the risk of respiratory infections, asthma, chronic respiratory symptoms, heart disease, and lung cancer among non- smokers.
Children living with smokers are particularly vulnerable because their lungs are still developing. Repeated exposure during childhood has been associated with reduced lung growth, more frequent asthma attacks, recurrent respiratory infections, and increased healthcare visits. For elderly individuals and those with pre-existing heart or lung disease, continuous exposure may worsen symptoms and accelerate disease progression. What begins as one person’s habit can therefore become a health burden for an entire household.
Beyond tobacco: Many households would never allow cigarette smoke indoors, yet routinely expose themselves to other sources of indoor pollution. The kitchen is one such source. Cooking is essential to daily life, but certain cooking practices generate significant amounts of particulate matter and other pollutants. High-temperature frying, grilling, roasting, and the use of biomass fuels can release fine particles that penetrate deep into the respiratory system.
A study by Kim and colleagues published in Environmental Research in 2019 demonstrated that cooking emissions can substantially increase indoor PM2.5 concentrations, particularly in poorly ventilated kitchens. The problem is especially relevant in households that continue to use wood, charcoal, agricultural waste, or other solid fuels for cooking.
According to the WHO Household Air Pollution Fact Sheet (2023), exposure to smoke generated from solid fuels remains a major contributor to respiratory disease worldwide. Long-term exposure has been associated with chronic bronchitis, chronic obstructive pulmonary disease (COPD), reduced lung function, and an increased risk of lung cancer. Fortunately, relatively simple measures such as kitchen chimneys, exhaust fans, improved cook stoves, and better ventilation can significantly reduce exposure.
Incense sticks and mosquito coils represent another often-overlooked source of indoor pollution. Their use is deeply embedded in daily life across many households. While they may appear harmless, both generate smoke containing fine particulate matter and potentially harmful chemicals. Research by Liu and colleagues published in the journal Indoor Air in 2003 demonstrated that mosquito coil smoke can generate substantial levels of particulate pollution within enclosed spaces.
Occasional use is unlikely to be harmful for most individuals, but prolonged daily exposure may contribute to respiratory irritation, particularly among children, older adults, and people with asthma.
Protecting our families: Improving indoor air quality does not necessarily require expensive technology. Several practical measures can substantially reduce exposure. Maintaining adequate cross-ventilation, using kitchen exhaust systems while cooking, keeping homes smoke-free, reducing unnecessary use of incense sticks and mosquito coils, regularly cleaning air-conditioning filters, and ensuring proper maintenance of gas stoves and appliances can all make a meaningful difference.
As physicians, we often focus on diagnosing and treating disease. Yet many illnesses are influenced by environmental factors that medications alone cannot address. Indoor air pollution rarely attracts headlines. It does not appear in weather forecasts or dominate public discussions. Yet it affects us every single day. While we may not always be able to control the quality of the air outside our homes, we can take meaningful steps to improve the air within them. In doing so, we protect not only our lungs but also the long-term health of our families and future generations.
