Spatial repellents work differently from the topical repellents people apply to their skin. Rather than masking the chemical cues that attract mosquitoes to human hosts or directly irritating their chemoreceptors on contact, spatial repellents disperse volatile compounds into the surrounding air that disrupt the mosquito’s host-seeking behavior from a distance. The World Health Organization currently recognizes only pyrethroid-based products as spatial repellents, including devices like MosquitoShield (containing transfluthrin), OFF! Mosquito lamps and Clip-Ons (containing metofluthrin), and ThermaCELL units (containing allethrin). While these synthetic compounds have demonstrated field efficacy, concerns about adverse effects from prolonged exposure in rodent studies have fueled growing consumer demand for plant-based alternatives.

The research team, led by April D. Lopez and senior author Immo A. Hansen, acquired seven batches of commercially available candles marketed as mosquito repellents, along with two control candles containing no essential oils at all. The products ranged from a simple unscented soy wax emergency candle to formulations containing up to 5 percent total essential oil content, with ingredient lists featuring combinations of citronella, lemongrass, rosemary, peppermint, cedarwood, lavender, eucalyptus, geranium, wintergreen, and corn mint. Not all manufacturers disclosed their exact essential oil concentrations, which the researchers noted as a significant limitation in evaluating product claims.

To test repellency, the team built a custom three-chamber taxis cage assay measuring 90 by 31 by 31 centimeters. Fifty female Aedes aegypti mosquitoes, aged 10 to 14 days and sugar-starved for at least four hours, were placed in the middle chamber. A human volunteer sat one meter upwind from the cage, and a pre-lit candle was positioned 31 centimeters from the cage between the volunteer and the mosquitoes. A small computer fan maintained a constant wind speed of 0.2 meters per second through the apparatus. After the chamber doors were opened remotely, mosquitoes were allowed to roam freely for ten minutes before being counted in each section. The researchers calculated percent attraction as the proportion of mosquitoes that moved toward the volunteer, and percent reduction in attraction by comparing candle trials to paired control trials without a candle.

The results revealed a stark divide among the products. In the absence of any candle, an average of 60 percent of mosquitoes were attracted to the human bait across all trials. Both control candles, one made of soy wax and one of bee’s wax, produced less than 15 percent reduction in attraction. However, three essential oil candles stood out dramatically: EO4 (Murphy’s Naturals Mosquito Repellent Candle), EO5 (Fabulous Frannie Essential Oil Candle Bug Away), and EO7 (Bug Bane Mosquito Repellent Candle) achieved mean reductions in attraction of 56 percent, 40 percent, and 45 percent respectively, significantly higher than both controls. The remaining three essential oil candles, including the well-known OFF! Citronella Candle and the Cutter Outdoor Candle, failed to produce statistically significant repellency despite their label claims.

To understand why some candles worked while others did not, the researchers turned to headspace solid-phase microextraction gas chromatography-mass spectrometry (HS SPME GC-MS), a technique that identifies the volatile organic compounds emitted by heated candle wax. They shaved 100 milligrams of unburned wax from each candle, equilibrated the samples at 40 degrees Celsius, and used an automated SPME Arrow fiber to extract airborne compounds for analysis on a triple quadrupole mass spectrometer. In total, 87 compounds were putatively identified across the seven essential oil candles, with compound identifications assigned by spectral matching to the Adams Essential Oil GC-MS library.

Principal component analysis of the volatile profiles showed clear separation between the high-repellency candles and the rest, indicating that the most effective products were compositionally distinct. The high-repellency candles also had greater mean total peak areas, suggesting that higher concentrations of active ingredients contribute to stronger repellent effects. Notably, EO4 and EO7 listed identical active ingredients on their labels, yet their chemical profiles did not completely overlap, pointing to the influence of essential oil sourcing, concentration, and manufacturing processes on the final volatile composition. The researchers also observed that monoterpenes made up a relatively high proportion of compounds across all candles, with EO4 and EO7 showing particularly high proportions of monoterpene hydrocarbons.

To pinpoint which specific compounds were most responsible for repellency, the team employed a LASSO regression model, a statistical approach well-suited to handling the high-dimensional data produced by GC-MS analysis. Using ten-fold cross-validation to determine the optimal shrinkage penalty, the model identified five compounds as the strongest predictors of spatial repellency. Citronellal, a monoterpene aldehyde and major constituent of citronella and lemongrass oils, received the highest positive coefficient, followed closely by trans-alpha-bergamotene, a sesquiterpene found in cedarwood and lavender oils. Ar-curcumene, another sesquiterpene present in cedarwood, citronella, and peppermint oils, also showed a positive association with repellency. Intriguingly, two compounds, dihydro carveol acetate and piperitol acetate, were negatively associated with repellency, suggesting that certain volatile components may actually undermine the overall protective effect of a candle’s formulation.

The findings carry significant practical implications for consumers and public health practitioners alike. Citronellal, the top predictor identified by the model, has been independently demonstrated as an effective mosquito repellent in multiple prior studies, lending confidence to the LASSO results. Trans-alpha-bergamotene and ar-curcumene have received less individual attention in the repellent literature, though both are constituents of essential oils from plants with known repellent properties. The identification of negatively associated compounds opens an entirely new avenue of investigation, as it suggests that candle formulation is not simply about maximizing concentration of known repellents but also about avoiding or minimizing compounds that may interfere with repellent activity.

The researchers caution that their laboratory assay, while highly sensitive, excludes environmental variables that matter under real-world conditions, including temperature, humidity, mosquito abundance, biting pressure, wind speed and direction, optical cues, and human movement. Earlier field studies of commercial citronella candles have produced contradictory results, with one reporting a 42 percent decrease in bites and another finding no repellency at all against Aedes, Culex, or Anopheles mosquitoes. The team recommends that field testing under diverse environmental conditions be conducted to inform label claims, and that further investigation of individual compounds and defined mixtures is needed to identify all active ingredients responsible for repellency. For now, the message to consumers is clear: not all mosquito repellent candles are created equal, and the efficacy of these products ultimately depends on their specific chemical formulation rather than on the mere presence of essential oils.

Subject of Research: Efficacy of commercially available essential oil-based candles as spatial repellents against Aedes aegypti mosquitoes

Article Title: The efficacy of commercially available essential oil-based candles as spatial repellents against Aedes aegypti mosquitoes – do they actually repel?

Article References: Lopez, A. D., Galvan, C. J., Holguin, F. O., Sroka, C. J., & Hansen, I. A. (2026). The efficacy of commercially available essential oil-based candles as spatial repellents against Aedes aegypti mosquitoes – do they actually repel?. Frontiers in Insect Science, 6, Article 1917728. https://doi.org/10.3389/finsc.2026.1917728

Image Credits: AI Generated

DOI: 10.3389/finsc.2026.1917728

Keywords: Aedes aegypti, essential oils, mosquito repellent, candles, spatial repellent, citronellal, volatile organic compounds, GC-MS, LASSO regression, vector-borne disease, pest management, citronella