The belief that eucalyptus can repel mosquitoes is a common one, rooted in the long history of using plant oils in traditional medicine to deter insects. The leaves of the lemon-scented gum tree, Corymbia citriodora, have been used for generations due to their distinct, strong aroma. This popular notion contains a kernel of truth, but the scientific effectiveness of a repellent depends entirely on how the plant material is processed. Understanding the difference between a raw plant extract and a refined commercial product is the most important step in choosing effective protection against biting insects.
The Definitive Answer: Eucalyptus vs. OLE
Raw eucalyptus essential oil is not registered by the Environmental Protection Agency (EPA) as an effective mosquito repellent and is not recommended by public health organizations. This unrefined oil contains compounds, but the concentration of the active ingredient is too low and too volatile to offer reliable, long-lasting protection. Scientific efficacy is found exclusively in a highly refined extract called Oil of Lemon Eucalyptus (OLE).
OLE is derived from the same Corymbia citriodora plant but undergoes a specific process to enrich its content of p-menthane-3,8-diol (PMD). PMD is the molecule responsible for the repellent action, and its concentration in OLE is significantly higher than in the essential oil form. This refined product is recognized as a biopesticide repellent, comparable in effectiveness to lower concentrations of synthetic repellents like DEET. The EPA and the Centers for Disease Control and Prevention (CDC) specifically endorse products containing OLE or PMD, while advising against the use of the unrefined essential oil.
How the Repellent Works
The active ingredient PMD does not kill mosquitoes; instead, it works by confusing the insect’s sensory system. Mosquitoes locate human hosts by detecting volatile chemical cues, especially carbon dioxide exhaled in breath and lactic acid emitted through skin. PMD effectively disrupts this process by interfering with the olfactory receptors on the mosquito’s antennae.
When applied to the skin, PMD creates a vapor barrier that essentially masks or jams the signals the mosquito is trying to read. This prevents the insect from properly sensing the human host, making it difficult for the mosquito to land and feed. This mode of action is a deterrent, causing the mosquito to avoid the treated area rather than poisoning it.
Safe and Effective Application
To ensure the best results, OLE products must be applied according to label instructions, typically containing an OLE concentration of around 30%. At this concentration, OLE provides protection for approximately five to six hours, comparable to many synthetic repellents. Reapplication is necessary if you are outdoors longer than the stated duration or if the repellent is washed off through swimming or heavy sweating.
The repellent should only be applied to exposed skin and clothing, never underneath clothing. To protect the sensitive areas of the face, spray the product onto your hands first and then carefully apply it, avoiding the eyes and mouth. OLE products are not approved for use on children under three years of age. Additionally, avoid applying the repellent to cuts, wounds, or irritated skin. When using sunscreen and repellent together, the sunscreen should always be applied first, followed by the OLE product.