Burning candles and incense at home? Researchers have a warning about your indoor air

As the evenings get darker and the heating goes on, many of us reach for scented candles or incense to make our homes feel cosier. A favourite fragrance can quickly change the atmosphere of a room, especially when we're spending more time indoors.

But how much attention do you pay to what's happening in the air while those scents fill the room? New research has put the spotlight on a familiar household habit, and the findings offer a good reason to rethink how we use these products during the colder months.

What researchers discovered about indoor air

A study published in Environment International in September 2026 looked at fine-particle pollution in 112 occupied London homes. The researchers measured tiny airborne particles known as PM2.5, which are small enough to travel deep into the lungs.

They recorded hourly peaks of up to 1,293 micrograms per cubic metre when incense was used, 858 for the oil diffusers included in the study and 622 for candles. In homes using these products, incense and oil diffusers each accounted for nearly half of measured bedroom PM2.5 exposure, while candles accounted for 14 per cent.

These are peak measurements, not averages for an entire day, so they shouldn't be interpreted as constant exposure. However, the study found that fragrance products could make a substantial contribution to indoor fine-particle pollution, particularly in smaller homes and rooms with inadequate ventilation.

Why burning candles can affect the air

A candle may look harmless when its flame is steady, but burning materials can release particles into the air. When a flame flickers or produces visible soot, incomplete combustion can contribute to the problem.

Incense also releases particles as it burns. Diffusers are a little different: they don't all work in the same way, and the study's findings about oil diffusers shouldn't automatically be applied to every type of fragrance diffuser.

The concern isn't entirely new, either. A 2025 study published in Scientific Reports examined how scented candles affected indoor air quality, adding to research into the particles released when candles burn.

In December 2025, the Associated Press also spoke to health experts about seasonal fragrances and indoor air pollution. Their advice was not to abandon every scented product, but to use them in moderation and take steps to reduce exposure.

How to enjoy candles with less indoor pollution

You don't necessarily have to give up candles to be more mindful of your indoor air. A few simple habits can help:

• Ventilate the room. Use existing ventilation and open a window when practical, including while burning candles and afterwards.
• Burn fewer candles at once. Several candles, incense and a fireplace can all contribute to indoor pollution.
• Keep the flame steady. Place candles away from draughts and follow the manufacturer's instructions for wick care.
• Avoid long sessions in closed rooms. Be particularly mindful of small spaces and bedrooms with limited airflow.
• Consider flameless candles. Battery-operated alternatives provide a similar glow without particles from a burning flame.

These recommendations are consistent with guidance from Waarzitwatin, the Dutch government-backed consumer information website, which advises ventilating rooms and limiting the number of candles burning at once. Asthma + Lung UK also provides advice on reducing indoor air pollution.

Who should be particularly careful?

People with asthma or other lung conditions may be more sensitive to indoor air pollution. Young children and older adults can also be more vulnerable to its effects.

That doesn't mean lighting a candle occasionally will automatically harm your health. Exposure depends on factors such as the product, how long it is used, the room's size and the amount of ventilation.

The takeaway is simple: you can still enjoy a cosy evening, but remember the air around you as well as the atmosphere you're creating. Using fewer burning products and keeping your home properly ventilated are sensible steps towards cleaner indoor air.