Candles create ambiance and pleasant scents that many people associate with comfort and relaxation, particularly during winter months and holiday seasons. But burning candles indoors releases particles, gases, and chemical compounds into enclosed spaces—some benign, others potentially problematic for air quality and health.
Understanding what candles actually produce when burned and implementing appropriate safety and air quality practices allows enjoyment of candles without unnecessary health risks or air quality degradation.
What Happens When Candles Burn
Combustion is never perfectly clean. All burning candles release substances into indoor air, though amounts and types vary by candle composition.
The Combustion Process
Complete combustion of candle wax would produce only:
- Carbon dioxide (CO₂)
- Water vapor (H₂O)
Reality: Combustion is never 100% efficient. Incomplete combustion produces:
- Particulate matter (soot and smoke particles)
- Carbon monoxide (CO)
- Volatile organic compounds (VOCs)
- Various other combustion byproducts
The extent of incomplete combustion depends on wick quality, wax type, air circulation, and burning conditions.
Particulate Matter from Candles
Burning candles produce fine particles that become airborne.
Soot formation: When flame doesn’t receive adequate oxygen or burns too hot, incomplete combustion creates soot—tiny carbon particles that appear as black smoke or deposit on surfaces near candles.
Particle sizes: Candle combustion produces particles across size ranges, including PM2.5 (particles ≤2.5 microns) that penetrate deep into lungs.
Concentration levels: Studies measuring PM2.5 from burning candles show:
- Single candle in small room: Can increase PM2.5 from 10 μg/m³ to 50-150 μg/m³
- Multiple candles: Can reach 200+ μg/m³
- For context, outdoor air quality is considered “unhealthy” above 55 μg/m³
Factors affecting particle production:
- Wick size (oversized wicks produce more soot)
- Draft conditions (flickering flames = incomplete combustion)
- Candle quality (poor quality wax and wicks produce more particles)
- Burning duration (longer burning often increases soot toward end of candle life)
Volatile Organic Compounds (VOCs)
From wax combustion: Even complete combustion of paraffin wax releases some VOCs as complex hydrocarbons break down.
From fragrance oils: Scented candles release fragrance compounds into air—these are VOCs by definition. While many are considered safe, some individuals are sensitive to these chemicals.
Specific compounds detected:
- Benzene (carcinogen, though typically in very small amounts)
- Toluene (can affect nervous system at high exposures)
- Formaldehyde (irritant and carcinogen at high concentrations)
- Acetaldehyde (irritant)
- Various fragrance chemicals
Context matters: Detection doesn’t equal danger. The concentrations produced by occasional candle burning in well-ventilated spaces are typically far below levels known to cause health effects. Chronic exposure in poorly ventilated spaces presents more concern.
Carbon Monoxide
Incomplete combustion produces CO—a colorless, odorless, potentially deadly gas.
Amounts from candles: Single candles produce minimal CO—typically not enough to raise indoor levels noticeably. However:
- Multiple candles burning simultaneously in small, poorly ventilated spaces can increase CO
- Candles combined with other combustion sources (gas stove, fireplace) contribute to cumulative CO levels
- CO detectors provide safety backup
Other Combustion Products
Nitrogen oxides: Produced in small amounts by high-temperature combustion.
Polycyclic aromatic hydrocarbons (PAHs): Formed during incomplete combustion. Some PAHs are carcinogenic, though amounts from candles are generally minimal.
Lead (historically): Candles manufactured before 2003 often used lead-core wicks. These released lead particles when burned. Now banned in United States, but imported or very old candles might still contain lead wicks.
Candle Wax Types and Air Quality Impacts
Different wax compositions burn differently and produce varying emissions.
Paraffin Wax
Composition: Petroleum-derived hydrocarbon wax. Most common candle wax historically.
Combustion characteristics:
- Burns at moderate temperature
- Can produce more soot than some alternatives if wick isn’t properly sized
- Releases petroleum-based VOCs when burned
Air quality concerns:
- Higher potential for soot production
- VOC emissions from petroleum compounds
- May contain chemical additives for color, scent, or burning properties
Research findings: Some studies suggest paraffin candles produce more concerning emissions than alternatives. However, well-made paraffin candles with proper wicks burn relatively cleanly.
Soy Wax
Composition: Derived from soybean oil. Popular “natural” alternative.
Combustion characteristics:
- Burns at lower temperature than paraffin
- Typically produces less soot
- Slower burn rate (longer-lasting candles)
Air quality benefits:
- Generally cleaner burning than paraffin
- Fewer soot problems when made properly
- Plant-based VOCs rather than petroleum-based
Considerations: “Natural” doesn’t mean emissions-free. Soy candles still produce combustion products, particulates, and VOCs—just potentially less than paraffin.
Beeswax
Composition: Natural wax produced by honeybees.
Combustion characteristics:
- Burns at high temperature
- Produces bright, steady flame
- Minimal soot production when made with quality wicks
- Natural honey scent
Air quality profile:
- Generally considered cleanest-burning wax
- Minimal VOC emissions
- Some claim negative ion production (scientific evidence limited)
Drawbacks: Expensive. Limited color options (naturally yellow/brown).
Palm Wax
Composition: Derived from palm oil.
Combustion characteristics:
- Similar to soy in burn temperature and cleanliness
- Crystalline appearance
Considerations: Environmental concerns about palm oil cultivation. Air quality profile similar to soy.
Blended Waxes
Many candles combine waxes (paraffin-soy blends, etc.). Performance depends on specific formulation.
Scented vs Unscented Candles
Fragrance adds another dimension to air quality considerations.
How Candles Are Scented
Fragrance oils: Synthetic or natural compounds added to wax. These vaporize when heated, releasing scent.
Essential oils: Natural plant extracts. Often marketed as healthier alternative to synthetic fragrances.
Air Quality Implications
VOC load: All fragrances are volatile organic compounds by definition. Scented candles release these VOCs intentionally.
Respiratory irritation: Fragrance compounds can irritate airways in sensitive individuals even if not toxic. Common complaints:
- Headaches
- Nasal irritation
- Coughing
- Asthma trigger
Phthalates: Some synthetic fragrances contain phthalates (chemicals used to make scents last longer). These are suspected endocrine disruptors. Many manufacturers now produce phthalate-free candles.
Sensitivity variation: Some people tolerate scented candles well. Others experience symptoms with any fragrance exposure. This is individual sensitivity, not necessarily toxicity.
“Natural” Fragrance Concerns
Essential oil-scented candles release natural VOCs, but “natural” doesn’t guarantee safety or lower irritation potential. Some essential oils are powerful irritants or allergens.
Wick Composition Matters
Wick material and construction significantly affect emissions.
Cotton Wicks
Standard choice: Most quality candles use cotton or cotton-paper combination wicks.
Benefits:
- Burns cleanly
- Minimal additives
- No metal emissions
Wood Wicks
Characteristics: Create crackling sound, larger flame profile.
Considerations: Can produce more soot than cotton wicks. Aesthetic/sound appeal rather than air quality benefit.
Metal-Core Wicks
Composition: Metal wire (zinc, tin) wrapped in cotton or paper.
Purpose: Keeps wick upright in large-diameter candles.
Concerns:
- Historically, lead was used (now banned in US)
- Zinc or tin cores are considered safe but some prefer to avoid all metal-core wicks
Identification: Bend wick. Metal core is firm and inflexible; pure cotton bends easily.
Safe Candle Burning Practices
Proper burning technique reduces emissions and fire hazards.
Burn Duration
First burn: Let candle burn long enough for entire top surface to melt (usually 2-4 hours). This prevents tunneling and ensures even burning throughout candle life.
General guideline: Burn 1 hour per inch of diameter (3-inch candle = 3-hour burn session).
Maximum duration: Don’t burn continuously for more than 4 hours. Let candle cool before relighting.
Wick Trimming
Trim to 1/4 inch before each burn. Long wicks:
- Create larger flames
- Produce more soot
- Increase fire hazard
Use wick trimmer or scissors. Remove trimmed portions from wax pool.
Ventilation
Critical for air quality: Burn candles in rooms with adequate air circulation.
Best practices:
- Don’t burn candles in completely sealed rooms
- Open window slightly if burning multiple candles
- Avoid burning in very small, enclosed spaces (bathrooms during showers, tiny closets)
Placement
Safety distances:
- 12 inches from flammable materials (curtains, papers, furniture)
- 3 feet between multiple burning candles
- Away from air vents or drafts (causes flickering and soot)
Surface: Heat-resistant, stable, level surface. Never leave burning on surfaces that could ignite or where candle could tip.
Extinguishing
Avoid blowing out: Blowing creates smoke and can spread hot wax.
Better methods:
- Candle snuffer (cuts off oxygen)
- Dip wick into wax pool with tool, then straighten (reduces smoke)
Ensure fully extinguished: Wick should not be glowing. Wait until no smoke visible.
How Many Candles Is Too Many?
No universal limit exists, but considerations include:
Room size: More candles in small room = higher pollutant concentrations.
Ventilation: Well-ventilated spaces handle more candles than sealed rooms.
Exposure duration: Occasional multiple candles (dinner party) differs from daily burning.
General guidance: 1-2 quality candles in typical room (200-300 sq ft) with normal ventilation = minimal concern. 5+ candles burning regularly in small, poorly ventilated spaces = questionable air quality.
Special Populations and Sensitivities
Asthma and Respiratory Conditions
Candle combustion products trigger asthma symptoms in some individuals. Fragrance compounds are particularly problematic.
Recommendations:
- Avoid or minimize candle use
- If burning, use unscented candles
- Ensure excellent ventilation
- Consider flameless alternatives
Children
Developing respiratory systems are more vulnerable to pollutants.
Considerations:
- Avoid burning candles in nurseries or children’s bedrooms
- Supervise candles in homes with young children (safety and air quality)
- Minimize exposure in general
Pregnancy
Some fragrance compounds may pose concerns during pregnancy (limited research).
Precautionary approach: Minimize scented candle exposure, focus on ventilation if burning candles.
Chemical Sensitivities
People with multiple chemical sensitivity (MCS) often cannot tolerate any candle burning.
Solution: Flameless alternatives only.
Alternatives to Traditional Candles
For those concerned about air quality impacts:
LED Flameless Candles
Advantages:
- No combustion products
- No fire hazard
- Realistic appearance improving (flickering LED)
- No air quality impact
Drawbacks:
- No real flame ambiance
- No scent (unless added separately)
- Require batteries
Essential Oil Diffusers
For fragrance without combustion:
- Ultrasonic diffusers create scented mist
- No combustion products
- Can control intensity
Considerations:
- Essential oils are still VOCs
- Can still trigger sensitivities
- Requires cleaning/maintenance
Beeswax Candles as Lower-Impact Option
If burning candles, beeswax represents cleaner-burning choice with minimal fragrance interference.
Measuring Candle Impact
Air quality monitors can objectively measure candle effects:
PM2.5 monitoring: Shows particle increase from burning. Typical indoor level 10-20 μg/m³ increasing to 50-150+ μg/m³ with candles.
VOC monitoring: Detects total VOC increase from fragrance and combustion.
CO detectors: Essential safety device, though candles rarely produce dangerous CO levels alone.
Value: Objective data replaces guesswork about whether candle use is affecting air quality.
The Research Perspective
Studies on candle emissions show:
Most candles produce measurable pollutants but amounts are typically well below levels causing acute health effects in occasional use.
Chronic exposure in poorly ventilated spaces has less research but raises more concern.
Individual variation in sensitivity means some people react to exposures others tolerate.
Quality matters: Well-made candles with proper wicks produce fewer emissions than cheap candles.
Regulatory Landscape
United States:
- Lead wicks banned (2003)
- No specific VOC or emission standards for candles
- General consumer product safety regulations apply
European Union:
- Stricter regulations on certain fragrance chemicals
- Labeling requirements for allergens
Voluntary standards: Some manufacturers follow voluntary guidelines (ASTM International) for candle safety and emissions.
The Bottom Line
Candles do impact indoor air quality through particle emissions, VOCs, and combustion products. The extent depends on:
- Candle quality and composition
- Burning practices
- Ventilation
- Frequency and duration of use
For most people: Occasional candle burning (1-2 candles, several hours weekly) in ventilated spaces poses minimal health risk.
For sensitive individuals: Candles can trigger symptoms. Minimizing use or choosing alternatives is appropriate.
For everyone: Proper burning technique, quality candle selection, adequate ventilation, and awareness of exposure reduce potential concerns.
Enjoying candles doesn’t require anxiety about air quality, but informed choices and sensible practices optimize the balance between ambiance and healthy indoor environments.