Mosquito coils and agarbatti smoke: what they do to your pet's lungs

A mosquito coil burns for six to eight hours and releases a concentrated mix of particulate matter, carbon monoxide, polyaromatic hydrocarbons, and pyrethroid insecticide compounds into the air. Agarbatti sticks produce a similar cocktail: fine particulate matter, volatile organic compounds, benzene, and formaldehyde, at levels that, in a small closed room, can exceed outdoor pollution benchmarks within minutes. For the person sitting upright near a window, the exposure is real but diluted. For a dog asleep on the floor, or a cat curled under a chair, the exposure is higher, longer, and happening inside a respiratory system that was not built for it.

Cats and dogs breathe at roughly two to five times the resting rate of an adult human. A cat at rest takes twenty to thirty breaths per minute; a dog, fifteen to thirty. More breaths per minute means more smoke pulled through the airways per hour. Pets also live at floor level, and smoke particulates, being denser than clean air, settle lower in a room. The animal breathing near the floor is breathing air that is measurably more polluted than the air at the height where the coil or stick is burning.

Cats carry an additional vulnerability. Their airway anatomy makes them prone to lower respiratory disease, and feline asthma is one of the more common chronic respiratory conditions seen in indoor cats. Smoke exposure does not cause feline asthma on its own, but it is a well-documented trigger for attacks in cats that already have the condition, and repeated exposure to airborne irritants is associated with airway inflammation in cats with no prior diagnosis. Dogs with flat faces, Pugs, French Bulldogs, Shih Tzus, Bulldogs, have structurally compromised airways to begin with. In these breeds, any additional airway irritation reaches a system that has very little reserve.

Fine particulate matter, classified by size as PM2.5 and smaller, passes through the nose and throat without being filtered. It reaches the bronchioles and, in sufficient quantity, the alveoli, the tiny air sacs where gas exchange happens. Once there, it triggers an inflammatory response. The airway lining swells, mucus production increases, and the cilia that normally sweep debris out of the lungs are damaged by repeated chemical irritation. Over time, this process looks like chronic bronchitis: a persistent cough, increased mucus, and reduced exercise tolerance.

Pyrethroid compounds, the active insecticides in most mosquito coils sold in India, are designed to act on insect nervous systems, and at the concentrations in a coil they are not acutely toxic to mammals through inhalation. The concern is not a single night's exposure, it is the cumulative effect of months or years of a coil burning in the same room where a pet sleeps. Benzene and formaldehyde, both present in agarbatti smoke, are classified carcinogens. Their role in canine nasal and lung tumours is an area of active veterinary research, and the evidence is not yet conclusive, but the mechanism, repeated mucosal irritation leading to cellular change, is well understood.

The signs of smoke-related respiratory irritation are easy to miss because they build gradually and look like minor ailments. A cough that comes and goes, especially after the coil has been burning for a few hours. Watery eyes or discharge at the inner corner. Sneezing more than usual. A cat that breathes with its mouth open, even briefly, is a sign that needs attention immediately, cats do not normally pant. A dog that tires faster on a walk than it used to, or that breathes audibly at rest, warrants a vet visit.

If you notice your pet coughing repeatedly, breathing with visible effort, ribs moving, nostrils flaring, belly pumping, or showing any bluish tint to the gums or tongue, stop reading and get to a vet now. Those are signs of acute respiratory distress, and no home adjustment will address them.

The simplest change is ventilation. A coil or agarbatti burning in a room with a window open and air moving through it produces far less indoor accumulation than the same coil burning in a closed room. If the coil is the only mosquito control available, burn it in a room the pet does not use, and let the smoke clear before the animal re-enters.

Physical barriers work better than chemical ones for pet households. Mosquito nets over sleeping areas, window mesh, and door screens keep mosquitoes out without putting anything into the air. Electric liquid vaporisers are a common alternative, but they also release pyrethroid compounds continuously into the room air, and a pet sleeping near the device gets a concentrated dose. They are not a safe substitute, they are a different delivery method for the same compound.

For agarbatti, the cultural and religious significance is real, and the answer is not to stop. It is to burn sticks near an open window or on a balcony, keep the pet out of the room while the stick is burning, and allow thirty minutes of ventilation before the animal returns. Charcoal-based or natural resin incense produces lower levels of benzene and formaldehyde than synthetic fragrance sticks, though no incense smoke is inert.

Pets that already have a diagnosed respiratory condition, feline asthma, chronic bronchitis, brachycephalic airway syndrome, should not share a room with burning coils or agarbatti under any circumstances. The vet managing that condition should know what the animal is regularly exposed to at home; it changes how triggers are assessed and how flare-ups are interpreted.