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Citronella Candles and Plant-Based Repellents

Citronella candles work a little, and mostly up close. One field trial found 42 percent fewer bites near citronella candles; an indoor trial put citronella candle repellency at 29 percent; a wind tunnel study found no effect. Plant oils evaporate fast. EPA registration is the dividing line: registered products were reviewed for effectiveness, exempt ones were not.

People have used plants to repel insects for thousands of years, and many plant extracts and oils genuinely repel mosquitoes. The trouble is duration and delivery. Here is what the trials measured and what EPA registration does and does not mean.

Do citronella candles actually reduce bites?

Some, in some settings, and the numbers are modest. One field trial ran in a deciduous woodlot in Guelph, Ontario, in the summer of 1995. Eight identically dressed subjects took five-minute biting counts at grid positions holding 3 percent citronella candles, 5 percent citronella incense, plain candles, or none. Subjects averaged 6.2 bites per 5 minutes at the citronella candle positions and 10.8 at untreated ones. The authors called the "overall reduction in bites provided by the citronella candles and incense" for the two formats "only 42.3 and 24.2%, respectively."

Indoors, in a high biting pressure setting in Israel, human landing assays put "the repellency rate of 5% citronella candles against mosquitoes" at 29.0 percent, against 85.4 percent for 5 percent geraniol candles. Outdoors, distance was decisive. At 1.0 m, citronella candles cut female mosquitoes caught in CDC traps by 35.4 percent, and "by increasing the distance to 2 m and 3 m, the repellency dropped significantly." A 2017 wind tunnel study measuring how many Aedes aegypti females were drawn toward a human reported that "the citronella candle had no effect." A Malaria Journal review sums up the field record: citronella and geraniol candles "are widely sold as outdoor repellents, however field studies against mixed populations of nuisance mosquitoes show reductions in biting around 50%, although they do not provide significant protection against mosquito bites."

The lesson is in the distance data. A candle loads the air right around it, and repellency dropped significantly at 2 m and 3 m. It does not replace CDC advice to empty and scrub water-holding containers once a week, which we cover in our standing water guide. See also our Asian tiger mosquito guide.

Why do plant oils wear off so fast?

Volatility. The Malaria Journal review states it directly: plant oils repel mosquitoes "with their effect lasting from several minutes to several hours. Their active ingredients tend to be highly volatile, so although they are effective repellents for a short period after application, they rapidly evaporate leaving the user unprotected." On citronella: "Initially, citronella ... is as effective dose for dose as DEET, but the oils rapidly evaporate causing loss of efficacy." The review puts citronella-based protection from host-seeking mosquitoes at "about two hours," while stressing that formulation matters a great deal.

The 2002 New England Journal of Medicine comparison tested 15 volunteers in a controlled laboratory environment with mosquito species, age, and hunger held constant. A soybean-oil-based repellent "protected against mosquito bites for an average of 94.6 minutes." Every other botanical product tested "provided protection for a mean duration of less than 20 minutes."

A 2011 meta-analysis reported its finding as a gap, not an absolute: using the cage method against Aedes, protection time for citronella oil "was less than that in the DEET (N,N-diethyl-m-toluamide) group, with a difference in protection time of 253 min (95% confidence interval: 169-336)." Its conclusion was that citronella products "are less effective than DEET products in terms of duration of protection," and that "adding vanillin to citronella oil products could prolong the protection time." The same review found that with the room method, citronella oil, alone or with vanillin, "provided complete repellency at least 3 h."

Ticks behave the same way. A CDC Emerging Infectious Diseases perspective describes a study running 19 exempt active ingredients as 10 percent lotion emulsions against female blacklegged ticks in the EPA-recommended human skin bioassay. Complete protection times ran from under 10 minutes for oils including castor and soybean, to more than 10 minutes but under an hour for a band that included citronella oil, up to 1 to 2 hours for cinnamon, clove, and geraniol oils. No exempt ingredient exceeded 2 hours; the DEET control held for the full 6-hour observation.

The picture is not uniform. The same perspective cites a laboratory study on nymphal castor bean ticks reporting "sustained repellency ... up to 8 hours after application of 10% solutions of citronella oil (83% repellency by the eight-hour time point), clove oil (78%), and geraniol oil (67%)," with "similar or better repellency than a 10% DEET solution," which held 71 percent at 8 hours. Duration numbers do not travel between species and test methods.

Which plant repellents carry EPA registration?

Both categories exist, and the same plant can appear in both. EPA's list of active ingredients in registered skin-applied repellents includes catnip oil, oil of citronella, DEET, IR 3535, p-Menthane-3,8-diol, oil of lemon eucalyptus, picaridin, and 2-undecanone. Next to oil of citronella, EPA notes "3 registered products; also used in unregistered products that meet the requirements for exemption from registration."

What registration buys is a review. EPA: "EPA registration of skin-applied repellent products indicates that they have been evaluated and approved for human safety and effectiveness when applied according to instructions on the label." CDC names six active ingredients found in registered products, DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, and 2-undecanone, tagging oil of lemon eucalyptus and 2-undecanone as plant-derived. The same list runs in CDC tick guidance, covered in our Lyme guide.

What does "exempt from registration" actually mean?

It means a safety judgment about the ingredients, and no effectiveness judgment about the product. EPA's own wording: "In the 1990s, EPA evaluated the active ingredients in these unregistered products for safety. We determined that the active ingredients posed minimal risk to human health in the percentages found in products on the market ... Note that products made from these ingredients have not been evaluated for effectiveness."

The ingredients EPA names as examples used in unregistered repellents are citronella oil, cedar oil, geranium oil, peppermint and peppermint oil, and soybean oil. Citronella and citronella oil both appear on EPA's list of active ingredients eligible for minimum risk pesticide products under 40 CFR 152.25(f). EPA adds that repellents without a registration number "have not been evaluated by EPA, and EPA cannot advise consumers about the effectiveness of these products."

One knock-on effect shows up on shelves: exempt labels cannot link a pest to a disease. Per EPA, such a label "may not say: 'controls ticks that carry Lyme disease;'" but can say "controls ticks."

Why does the CDC say no OLE or PMD under age 3?

p-Menthane-3,8-diol, the active component of oil of lemon eucalyptus, is the exception to the volatility problem, and it still carries an age restriction. EPA describes it as "a biochemical pesticide derived from eucalyptus plants" that "occurs naturally in the lemon eucalyptus plant," though "for commercial use, the active ingredient is chemically synthesized." The Malaria Journal review explains why it lasts: PMD "has a lower vapour pressure than volatile monoterpines found in most plant oils and provides very high protection from a broad range of insect vectors over several hours."

The restriction is specific and appears on both CDC prevention pages: "Do not use products containing OLE or PMD on children under 3 years old." The CDC Yellow Book gives the reason and one more warning in a single sentence. CDC "does not recommend using 'pure' oil of lemon eucalyptus (an essential oil that is not formulated) as a repellent because it has not undergone validated testing for safety and efficacy and is not registered with EPA as an insect repellent; in general, parents should not use products containing OLE or PMD on children <3 years old to avoid potential allergic skin reactions."

The bottle matters as much as the plant. A registered OLE repellent and a bottle of lemon eucalyptus essential oil are not the same product.

Do citronella wristbands and patches work?

The controlled tests are unkind to wearables. A semi-field study in Israel released 1,500 Aedes albopictus or 1,500 Culex pipiens into mesh-enclosed greenhouses and tested seven products, among them a wristband with 22 percent citronella oil and an oil of lemon eucalyptus adhesive patch. Result: "the sticker, transdermal patch, wristbands and sonic device did not provide significant protection to volunteers compared with the mosquito attack rate on control volunteers." The CDC Yellow Book puts it in one line: wearing "repellent-impregnated wristbands" is ineffective.

What if a plant-oil repellent irritates your skin?

Plant does not mean gentle. NPIC notes that oil of citronella "can be mildly irritating to the skin and eyes" and "may also cause skin allergies for some people with prolonged or frequent exposure," and that "some oil of citronella products should not be used on children less than six months old unless directed by a doctor." CDC's instruction if a reaction happens: wash the product off with mild soap and water, stop using it, and bring the container if you seek care. Any decision about a rash or a reaction in a child belongs with your clinician. For bites, see bite treatment.

Where Longsleeve fits

Longsleeve is an EPA-registered picaridin lotion (EPA Reg. No. 101457-1). It repels mosquitoes and ticks for up to 14 hours. It is fragrance-free, with nine disclosed ingredients.

Common questions

How long do citronella candles protect you?

Published trials report reduction in biting, not a protection window. A field study in Guelph, Ontario, published in 1996, measured a 42.3 percent overall reduction from 3 percent citronella candles. An indoor Israeli trial measured 29.0 percent repellency for 5 percent citronella candles, and outdoors repellency dropped significantly as distance rose past 1 m.

Is oil of lemon eucalyptus the same as lemon eucalyptus essential oil?

No. CDC "does not recommend using 'pure' oil of lemon eucalyptus (an essential oil that is not formulated) as a repellent because it has not undergone validated testing for safety and efficacy and is not registered with EPA as an insect repellent." EPA lists oil of lemon eucalyptus among active ingredients in registered skin-applied repellents, noting it contains PMD but is a separately regulated pesticide chemical.

Does a missing EPA registration number mean a repellent does not work?

It means nobody at EPA checked. EPA says products made from exempt ingredients "have not been evaluated for effectiveness," and that repellents without a registration number "have not been evaluated by EPA, and EPA cannot advise consumers about the effectiveness of these products." Some exempt formulations do well in individual studies; no agency review stands behind them.

Sources

  1. EPA, Skin-Applied Repellent Ingredients. https://www.epa.gov/insect-repellents/skin-applied-repellent-ingredients
  2. EPA, Regulation of Skin-Applied Repellents. https://www.epa.gov/insect-repellents/regulation-skin-applied-repellents
  3. EPA, Conditions for Minimum Risk Pesticides. https://www.epa.gov/minimum-risk-pesticides/conditions-minimum-risk-pesticides
  4. EPA, Active Ingredients Eligible for Minimum Risk Pesticide Products (December 2015). https://www.epa.gov/sites/default/files/2015-12/documents/minrisk-active-ingredients-tolerances-2015-12-15.pdf
  5. EPA, p-Menthane-3,8-diol (011550) Fact Sheet Summary. https://www3.epa.gov/pesticides/chem_search/reg_actions/registration/fs_PC-011550_01-Apr-00.pdf
  6. CDC, Preventing Mosquito Bites. https://www.cdc.gov/mosquitoes/prevention/index.html
  7. CDC, Preventing Tick Bites. https://www.cdc.gov/ticks/prevention/index.html
  8. CDC, About West Nile Virus. https://www.cdc.gov/west-nile-virus/about/index.html
  9. CDC Yellow Book, Mosquitoes, Ticks, and Other Arthropods. https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/mosquitoes-ticks-and-other-arthropods.html
  10. Eisen L. Efficacy of Unregulated Minimum Risk Products to Kill and Repel Ticks. Emerging Infectious Diseases, 2024;30(1). https://wwwnc.cdc.gov/eid/article/30/1/23-0813_article
  11. NPIC, Oil of Citronella Fact Sheet. http://npic.orst.edu/factsheets/citronellagen.html
  12. Maia MF, Moore SJ. Plant-based insect repellents: a review of their efficacy, development and testing. Malaria Journal, 2011;10(Suppl 1):S11. https://pmc.ncbi.nlm.nih.gov/articles/PMC3059459/
  13. Lindsay LR, Surgeoner GA, Heal JD, Gallivan GJ. Evaluation of the efficacy of 3% citronella candles and 5% citronella incense for protection against field populations of Aedes mosquitoes. Journal of the American Mosquito Control Association, 1996;12(2 Pt 1):293-4. https://pubmed.ncbi.nlm.nih.gov/8827606/
  14. Müller GC, Junnila A, Kravchenko VD, et al. Indoor protection against mosquito and sand fly bites: a comparison between citronella, linalool, and geraniol candles. Journal of the American Mosquito Control Association, 2008;24(1):150-3. https://pubmed.ncbi.nlm.nih.gov/18437831/
  15. Müller GC, Junnila A, Butler J, et al. Ability of essential oil candles to repel biting insects in high and low biting pressure environments. Journal of the American Mosquito Control Association, 2008;24(1):154-60. https://pubmed.ncbi.nlm.nih.gov/18437832/
  16. Fradin MS, Day JF. Comparative efficacy of insect repellents against mosquito bites. New England Journal of Medicine, 2002;347(1):13-18. https://pubmed.ncbi.nlm.nih.gov/12097535/
  17. Kongkaew C, Sakunrag I, Chaiyakunapruk N, Tawatsin A. Effectiveness of citronella preparations in preventing mosquito bites: systematic review of controlled laboratory experimental studies. Tropical Medicine and International Health, 2011;16(7):802-10. https://pubmed.ncbi.nlm.nih.gov/21481108/
  18. Revay EE, Junnila A, Xue RD, et al. Evaluation of commercial products for personal protection against mosquitoes. Acta Tropica, 2013;125(2):226-30. https://pubmed.ncbi.nlm.nih.gov/23092689/
  19. Rodriguez SD, Chung HN, Gonzales KK, et al. Efficacy of some wearable devices compared with spray-on insect repellents for the yellow fever mosquito, Aedes aegypti (L.) (Diptera: Culicidae). Journal of Insect Science, 2017;17(1):24. https://pubmed.ncbi.nlm.nih.gov/28423421/

Last reviewed 2026-08-06 · every claim on this page is sourced above