Do All Candles Produce Formaldehyde?
Yes, all candles produce formaldehyde when burned, as it is a natural by-product of combustion processes, though the amounts vary significantly based on candle composition and burning conditions.
Formaldehyde as a Combustion By-Product
Formaldehyde is inherently produced during incomplete combustion of organic materials, which occurs whenever candles burn 1. This is not unique to candles but applies to all combustion processes involving carbon-based fuels 1.
Evidence from Candle Emission Studies
Research consistently demonstrates formaldehyde emissions from all candle types:
Scented candles emit formaldehyde at concentrations ranging from 925 ppb to 2098 ppb when lit, with strawberry-scented candles showing the highest emissions (2098 ppb), followed by clean cotton (1022 ppb) and plain unscented candles (925 ppb) 2
Both scented and unscented candles produce formaldehyde, confirming this is a universal combustion product rather than fragrance-related 3, 2
Formaldehyde emissions occur regardless of wax composition (paraffin, soy, beeswax) or wick type, though the specific amounts may vary 4, 3
Factors Affecting Emission Levels
The quantity of formaldehyde produced depends on burning conditions:
Stressed burning (fluctuating air velocities, drafts) increases emissions of various pollutants including formaldehyde 4
Wax and wick composition influence overall emission profiles but do not eliminate formaldehyde production 4
Emissions vary throughout the burn time, with some candles showing different emission patterns as they burn down 4
Health Context and Risk Assessment
The health significance depends on exposure levels and duration:
The WHO guideline for formaldehyde is 100 μg/m³ (approximately 81 ppb) based on 30-minute averaging time 1
Formaldehyde is classified as Group 1 carcinogen by IARC, though cancer risk in humans is primarily associated with high occupational exposures (thousands of ppb) 1
Moderate exposure levels (hundreds of ppb) cause irritant symptoms including eye/nose burning and sore throat 1
Most residential formaldehyde concentrations are below 25 μg/m³, though candle burning can temporarily elevate levels 1
Exposure Scenarios
Calculated indoor concentrations from candle burning:
Under typical indoor use scenarios, formaldehyde concentrations from candles generally remain below guidance values 3, 5
Even when multiple candles burn simultaneously in small rooms, concentrations typically stay below 1% of occupational limit values 5
However, poor ventilation and prolonged burning can lead to accumulation approaching or exceeding short-term guideline values 2
Practical Implications
To minimize formaldehyde exposure from candles:
Ensure adequate ventilation when burning candles indoors 4, 3
Avoid "stressed burning" conditions by keeping candles away from drafts and air currents 4
Limit burn duration and number of candles burned simultaneously in enclosed spaces 4, 5
Trim wicks regularly to promote complete combustion 4
Important Caveats
The question of whether candles pose significant health risks remains context-dependent. While formaldehyde production is universal, actual health impact depends on ventilation, room size, burn duration, and individual susceptibility 1, 3. Individuals with respiratory conditions or formaldehyde sensitivity should exercise particular caution 1.