Citronella candles are a popular solution for deterring insects, often marketed as a natural alternative to chemical sprays. This reputation stems from the plant-derived citronella oil, which is an effective insect repellent. However, burning the candle introduces combustion, fundamentally changing the safety profile. The primary toxicity concern involves the chemical compounds released when the entire product is burned, not just the essential oil itself.
Toxicity Profile of Citronella Oil and Combustion Byproducts
The citronella oil component is derived from the leaves and stems of the Cymbopogon grass species, containing active molecules like citronellal, citronellol, and geraniol. The U.S. Environmental Protection Agency (EPA) classifies citronella oil as a biopesticide with a low intrinsic risk. When used topically in approved concentrations, it is generally considered safe, though it can cause skin irritation. Serious toxicity is primarily a risk only if the concentrated oil is ingested in large quantities, particularly by small children.
The primary health concern comes from the act of burning itself, which generates combustion byproducts. Burning the candle wax, especially paraffin wax, and the wick releases fine particulate matter (PM 2.5) and Volatile Organic Compounds (VOCs) into the surrounding air. These invisible emissions are a form of indoor air pollution, even when the candle is used outdoors near open windows. Common VOCs released include chemicals like benzene, toluene, and formaldehyde, which are linked to various health issues.
Respiratory and Allergic Concerns for Humans and Animals
The combustion byproducts pose a direct respiratory risk to humans, particularly those with pre-existing lung conditions. Inhaling fine particulate matter (PM 2.5) can cause irritation to the eyes, nose, throat, and lungs. For individuals with asthma or Chronic Obstructive Pulmonary Disease (COPD), exposure to these compounds can exacerbate symptoms and potentially trigger respiratory distress. Direct contact with the citronella oil itself can also cause contact dermatitis or allergic reactions in sensitive individuals.
The risk to household pets, especially cats, is significantly greater due to a fundamental biological difference in metabolism. Cats lack a specific liver enzyme (glucuronyl transferase or UGT) necessary to process and eliminate phenolic compounds, such as citronellal and geraniol, found in essential oils. This metabolic deficiency means that even small amounts of inhaled oil fumes or residue on the fur can accumulate in their system, leading to potential liver damage.
Exposure can result in a range of symptoms, including respiratory distress, drooling, vomiting, loss of balance, and in severe cases, liver failure. Burning citronella candles indoors is strongly discouraged, as the concentrated fumes pose a serious and potentially life-threatening toxicity risk to cats. Dogs are less susceptible because they possess the necessary liver enzymes, but they can still experience respiratory irritation from the smoke and fumes.
Safe Application and Alternative Insect Repellents
Using citronella candles safely requires strict adherence to outdoor use guidelines and ventilation awareness. Always burn the candle in a well-ventilated outdoor area, keeping it far from open windows or doors to prevent smoke and VOCs from drifting indoors. It is advisable to trim the wick to about one-quarter inch before each use, as this action helps reduce the production of soot and fine particulate matter. Never leave a burning candle unattended, and ensure it is placed where pets, especially cats, cannot access it or inhale the concentrated fumes.
Safer and more effective alternatives exist that do not rely on combustion for insect control. The most effective natural alternative is oil of lemon eucalyptus (OLE), which is the only plant-based repellent recommended by the Centers for Disease Control and Prevention (CDC) for its effectiveness. Synthetic repellents like picaridin are also highly effective and generally well-tolerated by humans. Simple physical barriers, such as using electric fans on patios to disrupt mosquito flight paths, can also provide a non-toxic layer of protection.