Do Candles Produce Carbon Monoxide? Safety Facts You Need to Know
A lot of people ask whether candles give off carbon monoxide. The short answer is yes. Any open flame makes a little, but a candle makes far less than the things that usually cause trouble at home, like furnaces, gas heaters and car exhaust. Here's what the research says and the simple ways to keep candle use safe indoors.
How Carbon Monoxide Forms When Things Burn
Carbon monoxide forms when something burns without getting enough oxygen. Think of a campfire that's been smothered. Instead of burning completely, it starts producing smoke and other unwanted gases. The same thing applies to candles, just on a much smaller scale.
When you light a candle, ideally the flame gets plenty of fresh air and burns the wax completely, turning it mostly into carbon dioxide and water vapor. But conditions aren't always perfect, and that's when the question comes up: do burning candles produce carbon monoxide in amounts that matter?
If you look closely at a candle flame, you'll notice different colors. The blue part at the base is where fuel is burning most completely. A tall, flickering yellow or orange flame, or one giving off black smoke, usually means the burn isn't as complete as it could be. That incomplete burning is what creates small amounts of carbon monoxide.
What Research Tells Us About Candles and Carbon Monoxide
Scientists have studied this. In a 2021 study published in Environment International, researchers burned 24 types of scented and unscented candles in a test chamber and measured carbon monoxide, nitrogen oxides, particles and other compounds. When they used those numbers to estimate levels in typical rooms, most results came out well below indoor guidance values. The exceptions they flagged were nitrogen dioxide, acrolein and benzo[a]pyrene in some scenarios, not carbon monoxide.
For context, the EPA says carbon monoxide levels in homes without gas stoves usually run between 0.5 and 5 parts per million. There's no official indoor standard, but the U.S. outdoor air standard is 9 ppm averaged over 8 hours. A candle or two in a room with some air movement isn't the kind of source that gets a home anywhere near that.
What Makes Some Candles Produce More Carbon Monoxide
A few things affect how completely a candle burns. Wick size is a big one. If the wick is too long, the flame gets bigger than it should and may not get enough oxygen to burn completely. That's why some candles have flames that dance around or send up black smoke.
The wax matters too. Researchers in Italy who tested container candles found that carbon monoxide and particle emissions had more to do with the quality of the wax than with additives. Well-made candles with properly sized wicks are the safer bet, whatever the wax.
Ventilation plays a huge role. With some air circulation, the flame gets fresh oxygen and any combustion byproducts get carried away. In a stuffy room with no air movement, even a small flame can start to struggle.
How you care for your candles makes a difference as well. If you never trim the wick, it keeps getting longer and makes a bigger flame. A wick that's been burning a long time can also build up a carbon "mushroom" on top, which makes the flame smoky.
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Different Types of Candles and Their Emissions
Soy candles, beeswax, coconut blends and paraffin all make some carbon monoxide when they burn, because they're all fuel and a flame. The 2021 study above tested several wax types and found that, in most cases, none of them pushed estimated room levels past guidance values.
Paraffin candles are the most common type in stores. Quality paraffin candles with properly sized wicks burn fine under normal conditions. The bigger difference is between well-made candles and very cheap ones that may have oversized wicks or poor-quality wax.
Specialty candles, like gel candles or ones with decorations pressed into the wax, vary a lot depending on what's in them, so the same rules apply: watch the flame and keep the wick trimmed.
Health Considerations and Who Should Be Extra Careful
Some people are more sensitive to carbon monoxide than others. According to the CDC and EPA, infants, older adults, people with heart disease, anemia or breathing problems, and unborn babies are more likely to be affected.
The early symptoms of carbon monoxide exposure are easy to brush off: headache, dizziness, weakness, upset stomach and confusion. The CDC describes them as "flu-like." Candles on their own rarely produce enough to cause these symptoms, but they add to whatever else is in your home's air.
The places we like to burn candles, like bedrooms, bathrooms during a bath, or small living areas, can hold onto combustion byproducts more easily than larger, airier rooms. That's why a little ventilation matters.
If you're pregnant, it's worth being a bit more careful with any source of carbon monoxide, candles included, and keeping rooms ventilated when you burn them.
Simple Ways to Burn Candles Safely
The good news is that safe candle use is pretty simple. The most important thing is to keep your candle wicks trimmed to about 1/4 inch before each use. That keeps the flame the right size. Long wicks make large, unstable flames that are more likely to smoke.
Ventilation doesn't have to be complicated. Crack a window or run a fan when you're burning candles, especially in smaller rooms. You don't need a strong breeze, just some air movement.
When shopping for candles, look for quality over bargain prices. Candles with cotton or wood wicks are a good choice, and so are natural wax candles, though a well-made paraffin candle burns fine too.
Never leave candles burning when you're not around to keep an eye on them, and never overnight. Besides the fire risk (the NFPA reports that candles start thousands of home fires a year), an unattended candle can drift into a smoky burn. If the flame gets very large, flickers a lot, or gives off black smoke, blow it out and trim the wick before relighting.
Want the scent with no flame at all? Wax Melt Dots in an electric warmer give you fragrance without burning anything.
Carbon Monoxide Detectors: Your Safety Backup
Even though candles make very little carbon monoxide, detectors are still a smart idea. They protect you from every source, not just candles. Furnaces, water heaters, gas appliances and car exhaust from an attached garage are much more likely to cause problems.
The CDC recommends battery-operated or battery-backup detectors near every sleeping area. A detector with a digital readout can also show you the highest level it has picked up, in addition to sounding an alarm.
Check the batteries when you change your clocks in spring and fall, and replace the detector according to the manufacturer's instructions or about every 5 years. A detector that isn't working can't protect you.
The Bottom Line on Candles and Carbon Monoxide
So, do candles produce carbon monoxide? Yes, but a small amount, and research suggests it stays well below guidance levels with normal use. Trim your wicks, give the room a little ventilation, never leave a candle burning unattended, and keep working CO detectors in your home.
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Frequently Asked Questions
Can burning too many candles at once cause carbon monoxide poisoning? More candles do mean more carbon monoxide. In normal home use with some ventilation, it's very unlikely to reach a dangerous level, but don't burn a crowd of candles in a small, closed room, and keep a CO detector nearby.
Are scented candles more likely to produce carbon monoxide than unscented ones? Not necessarily. Research has linked fragrance more to other emissions, like aldehydes, than to carbon monoxide. Wick size and wax quality matter more for carbon monoxide than whether the candle is scented.
How long can I safely burn a candle in a closed room? There's no official time limit, but it's always best to have some ventilation. Cracking a door or window slightly makes a real difference in most rooms.
Should I be worried about carbon monoxide if I only burn candles occasionally? Occasional candle use is a very small source. What matters more is having working detectors and well-maintained fuel-burning appliances.
Can I use my car's carbon monoxide detector to check candle safety? It's better to use a detector made for homes and follow its instructions for placement.
Are there any candles that produce zero carbon monoxide? Any candle with a flame produces some. Flameless options like electric candles or wax melts in an electric warmer produce none.
Want to read about soy allergy symptoms? Check out our blog HERE.
References
- Salthammer, T., et al. (2021). "Measurement and evaluation of gaseous and particulate emissions from burning scented and unscented candles." Environment International. https://doi.org/10.1016/j.envint.2021.106590
- U.S. Environmental Protection Agency. "Carbon Monoxide's Impact on Indoor Air Quality." epa.gov
- U.S. Environmental Protection Agency. "What is the average level of carbon monoxide in homes?" epa.gov
- Centers for Disease Control and Prevention. "Carbon Monoxide Poisoning Basics." cdc.gov
- American Lung Association. "Carbon Monoxide." lung.org
- Ahrens, M. (2020). "Home Candle Fires." National Fire Protection Association. nfpa.org
- Derudi, M., et al. (2012). "Emissions of air pollutants from scented candles burning in a test chamber." Atmospheric Environment. https://doi.org/10.1016/j.atmosenv.2012.03.027
- Derudi, M., et al. (2014). "Emission of air pollutants from burning candles with different composition in indoor environments." Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-013-2394-2