Cedar wood is often believed to naturally repel mosquitoes, a reputation stemming from its distinct, strong scent and traditional use in chests and closets for moth protection. Scientific investigation into this claim, however, reveals a more complex reality than common folklore suggests. This article examines the specific chemical components of cedar and analyzes the scientific evidence to determine its true effectiveness against mosquitoes.
The Chemical Basis of Cedar’s Reputation
Cedar wood, particularly from species like Eastern Redcedar (Juniperus virginiana), contains a complex mixture of volatile organic compounds (VOCs) responsible for its characteristic aroma. These compounds, primarily terpenes and sesquiterpenes, are what the tree uses as a natural defense mechanism against pests. The most significant compound is Cedrol, a sesquiterpene alcohol that constitutes between 15% and 19% of the oil extracted from Virginia and Texas cedarwood, respectively.
Other prominent VOCs include Cedrene and Thujopsene, which also contribute to the wood’s strong scent and biological activity. These aromatic molecules are believed to interfere with an insect’s sensory perception, essentially confusing them or acting as a low-level insecticide. Cedrol is known to disrupt the behavior and nervous systems of various insects, which is the basis for cedar’s historic use as a deterrent.
Scientific Findings on Mosquito Repellency
Despite the chemical potential, controlled studies on the direct repellent effect of cedar oil against mosquitoes have yielded mixed results. In one laboratory study testing cedarwood oil on human skin, the oil failed to repel Aedes aegypti and Anopheles albimanus mosquitoes, even when tested at a 100% concentration. This suggests that cedar oil, when applied topically, does not provide a reliable or long-lasting barrier against mosquito bites.
The oil does show promise in other forms of mosquito control, particularly as an insecticidal agent. Cedarwood oil is recognized for its larvicidal properties, meaning it can kill mosquito eggs and larvae when applied to water. Concentrated mixtures containing cedarwood oil have demonstrated high efficacy in knockdown and mortality against adult Aedes aegypti mosquitoes. For example, a blend containing 25.3% cedarwood oil was effective in killing mosquitoes in semi-field evaluations, indicating its potential as an area insecticide rather than a personal repellent.
Comparing Cedar Oil and Passive Wood Products
The distinction between concentrated cedar essential oil and passive cedar wood products is crucial when assessing mosquito control. Cedar essential oil, concentrated through distillation, contains the high percentage of VOCs necessary to exert a biological effect. This concentrated oil is typically used in sprays or diffusers for short-term application, offering the only realistic chance for mosquito deterrence.
Passive products, such as cedar mulch, shavings, furniture, or fencing, release their volatile compounds at a much lower rate and concentration. The aromatic compounds dissipate quickly into the open air, making the concentration too low to be effective at repelling mosquitoes from a wide area. Relying on cedar mulch or wood chips for effective outdoor area repellency against mosquitoes is not supported by science due to the rapid dilution and low concentration of active compounds.
Real-World Limitations and Effective Alternatives
A primary limitation of cedar oil and other botanical repellents is the rapid evaporation of the volatile compounds, which significantly limits the duration of protection. This short lifespan requires frequent reapplication, often every hour or two, for any measurable effect. Safety is also a concern, as undiluted cedar essential oil can cause skin irritation, necessitating proper dilution before topical use.
While the U.S. Environmental Protection Agency (EPA) recognizes cedarwood oil as a minimum-risk pesticide, this designation does not guarantee high efficacy against mosquitoes. Products containing cedar oil are generally exempt from the rigorous testing required of other repellents. For reliable, proven protection, the EPA and the Centers for Disease Control and Prevention (CDC) recommend using repellents that contain active ingredients such as DEET, Picaridin, or Oil of Lemon Eucalyptus (OLE), which have been thoroughly tested for both safety and effectiveness.