Cinnamon essential oil (CEO) is derived from the bark or leaves of trees belonging to the Cinnamomum genus, such as Cinnamomum zeylanicum or Cinnamomum cassia. This oil has a potent, spicy fragrance. Science has begun to address whether this aromatic oil is truly effective as a modern insect repellent.
Repellent Effectiveness Against Common Pests
Cinnamon essential oil is an effective repellent, though its performance depends on the concentration used and the target pest species. Research on mosquitoes, such as Aedes aegypti, shows that a 5% concentration can provide protection for over 60 minutes. This concentration reduces the number of mosquito bites by 50% to 60%.
The oil also shows strong efficacy against household pests, including ants and flies. Field tests document a significant reduction in ant trails, sometimes showing a drop in activity of 65% within 24 hours of application. Cinnamon oil exhibits insecticidal properties against house flies (Musca domestica), achieving 100% mortality at a 10% concentration. Plant-based oils like CEO generally require more frequent reapplication than conventional synthetic repellents to maintain their protective barrier.
The Mechanism of Repulsion
Cinnamon essential oil’s effectiveness comes from its high concentration of specific aromatic compounds. The two primary active molecules are cinnamaldehyde and eugenol. Cinnamaldehyde is typically the most abundant compound in cinnamon bark oil, while eugenol is often dominant in the leaf oil.
These molecules affect insects through a dual mechanism, acting as both a repellent and a biocide. At low concentrations, cinnamaldehyde disrupts the insect’s chemoreceptors, the sensory organs used to detect food and hosts. By confusing the insect’s sense of smell, the oil makes the treated area unappealing. At higher concentrations, the compounds act as neurotoxins, impacting the insect’s nervous system.
Safe Topical Application and Environmental Use
Due to the potency of its active components, cinnamon essential oil must be diluted before being applied to the skin. Applying concentrated oil directly can cause severe skin irritation, chemical burns, or sensitization, as it is classified as a “hot oil.” For topical use, a safe dilution range is 0.5% to 1.0% essential oil mixed with a carrier oil, such as jojoba, coconut, or almond oil.
Before using any new formulation, a small patch test on an inconspicuous area of skin is recommended to check for adverse reactions. For environmental use, a diluted spray can be applied to outdoor furniture or non-porous surfaces to deter pests like ants and mosquitoes.
A significant safety concern is the use of cinnamon oil around household pets, especially cats. Cats lack a specific liver enzyme needed to metabolize cinnamaldehyde and other phenolic compounds, making it highly toxic. Both direct skin contact and inhaling the oil from diffusers can lead to poisoning. It is advised to avoid using cinnamon essential oil in areas accessible to cats and to exercise caution with dogs, as it is potentially toxic to canines.