Candles and candle warmers deliver fragrance using fundamentally different processes. A burning candle uses a wick and an open flame, relying on combustion to release scent. A candle warmer uses a controlled electric heating element to melt the wax without ignition. This distinction between fire-based combustion and gentle, flameless heat significantly impacts indoor air quality and health.
The Mechanics of Scent Release
The process of scent release in a traditional candle depends on high heat. The flame’s heat vaporizes the wax and fragrance oils, which are then combusted to produce light, heat, and the desired aroma. This combustion requires the wax pool temperature to reach hundreds of degrees Fahrenheit, well above the flashpoint of the wax and most fragrance ingredients. This high temperature converts the components into a gaseous form that sustains the flame.
A candle warmer, whether a hot plate or a lamp, operates at a much lower, regulated temperature. The goal is only to melt the wax, not to burn it. This gentle heat allows fragrance oils to evaporate slowly from the melted wax pool, a process called volatilization. Since the wax is heated below its flashpoint, no combustion takes place, and the chemical structure of the wax and fragrance is largely preserved.
Airborne Particulates and Soot
One noticeable difference between the two methods is the presence of soot and particulate matter. The incomplete combustion of carbon-based wax and wick material generates microscopic airborne particles. This particulate matter (PM 2.5) can penetrate deep into the lungs and potentially enter the bloodstream, posing a risk to cardiovascular and respiratory health.
Candles made from paraffin wax, a petroleum byproduct, release higher amounts of soot, which can contain carcinogenic chemicals similar to those found in diesel exhaust. The type of wick, such as those with metal cores, can also contribute to airborne particulate pollution. Candle warmers eliminate this physical pollutant entirely because they operate without a flame or wick, preventing the combustion reaction that creates soot and smoke.
Volatile Organic Compounds and Chemical Exposure
Both methods release Volatile Organic Compounds (VOCs), which are chemicals that easily become vapors or gases at room temperature. For a burning candle, the high heat of the flame causes thermal degradation of the wax and fragrance oils, releasing toxic VOCs like benzene, toluene, and formaldehyde. These compounds are known to irritate the respiratory tract and can cause headaches or dizziness.
While candle warmers avoid combustion, they still release VOCs as fragrance oils evaporate from the melted wax. Recent research indicates that scented wax melts can emit large quantities of VOCs due to their higher fragrance concentration and maximized surface area. These evaporated fragrance compounds, specifically monoterpenes, can react with naturally occurring ozone in indoor air. This chemical reaction, known as ozonolysis, results in the formation of airborne nanoparticles (1 to 100 nanometers). Studies have found that the resulting nanoparticle concentrations from scented wax melts can be comparable to those emitted by combustion-based sources like traditional candles.