A scented candle can add a cosy atmosphere to a party or quiet night in. But if you’ve ever watched those wisps of smoke or looked at the resulting soot and wondered whether it's really safe to breathe that in, read on.

Candles, whether scented or unscented, do release particles as they burn, so it’s natural to wonder if your air quality is being affected.

'Paying attention to the air quality in your home is an important part of staying in good health,' says Dr Daniel Croft, associate professor of pulmonary and critical care medicine at University of Rochester Medical Center. Poor indoor air quality can cause unpleasant symptoms like irritated eyes, a sore throat, headaches and respiratory issues.

The good news: you don’t have to give up your favourite scented candles altogether. Here are some tips to enjoy a dimly-lit evening, and also look after your health.

Is it dangerous to burn candles?

‘Burning candles in indoor spaces can increase the risk of inhaling soot from the smoke, as well as organic compounds called VOCs and particulate matter (PM),’ says Dr Meghan E Rebuli, a respiratory toxicologist and assistant professor of paediatrics at the University of North Carolina at Chapel Hill. 'A variety of studies have mostly found that the amount of soot, VOCs, and PM produced are well below the threshold of concern, That said, some types of candles may slightly increase the amount of chemicals and particles in the indoor space, especially paraffin wax-based candles and fragranced candles.'

What are the health risks of burning candles?

Research has shown that inhaling particulate matter over long periods of time is linked to asthma attacks, exacerbations of chronic obstructive pulmonary disease (COPD) and increased risk of cardiac events as well as stroke and other neurologic conditions.

'The most important thing to know is that in toxicology, the dose makes the poison,' says Dr Croft. 'So, it's worth thinking about the size of the candle, the amount of time it's left burning and the size of the room. Ventilation is absolutely the most important factor when we think about indoor air quality.'

For most people, scented candles are harmless. A 2023 study done by the Research Institute of Fragrance Materials FIM found that any exposure to toxins when using scented candles is too low to worry about.

But people with with asthma and allergies – as well as pregnant women – should pay closer attention to any potential air pollution exposures and do what they can to minimise them (like opening windows to create ventilation).

How to burn that candle extra-safely

  1. Invest in an air purifier. 'Indoor air cleaners using HEPA filters do a great job at clearing particles from the air,' says Dr Croft. However, he notes, the combustion of candles releases gaseous pollutants to the air, which the particle filters will not catch. 'Some have charcoal filters to try to absorb the gaseous particles, but those need to be changed regularly or they become saturated and ineffective,' he says.
  2. Make sure the room is ventilated. This advice applies whether you’re lighting a candle or using a gas stove. 'Ventilation is the best way to get rid of gaseous air pollutants within homes,' says Dr. Croft. 'Crack the window open or turn to the nearby bathroom that has an exhaust fan and turn that up. Try to ventilate the space by any means necessary to try to keep the air moving.'
  3. Trim the wick before you light. This will create a smaller flame and as a result, less smoke and soot will be released into the air.
  4. Set a timer. 'Do not burn your candle for extended periods of time – more than a few hours – to reduce the dose of exposure to potentially harmful compounds,' says Dr Rebuli.
  5. Don’t blow candles out. 'Extinguish the candle with a snuff or by dipping the wick in wax to reduce exposure to soot and smoke,' suggests Dr Rebuli. You can buy a metal ‘wick dipper’ to do this, or just use an old butter knife to push the wick down into the liquid wax and then push it upright again.'