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Compound Monograph

Citronellal

Citronellal is the monoterpene aldehyde of citronella, lemongrass and lemon eucalyptus oils — a lemony fragrance ingredient, natural-repellent building block, and preclinical antifungal and rodent sedative. The reduced aldehyde relative of citronellol, and an EU-labelled skin sensitiser; no human trials of the isolate.

Work in progress

Classification

Citronellal is a monoterpene aldehyde, part of the terpenoids class. The largest class of plant compounds, built from five-carbon isoprene units — the essential-oil aromatics, resins, bitter principles, saponins, and plant sterols.

Terpenoids Monoterpenes

Where Does It Come From? (7)

Citronellal is a naturally occurring monoterpene aldehyde, found in Citronella grass, Lemongrass, Lemon balm / melissa and 4 other sources. It is well tolerated orally (low toxicity).

CitronellaCitronella grassLemon balm / melissaLemon eucalyptus Lemongrass Cymbopogon citratus Manuka Leptospermum scoparium Melissa Melissa officinalis

Pharmacology & Research

Citronellal is the monoterpene aldehyde of citronella, lemongrass and lemon eucalyptus oils — the reduced-then-oxidised relative of the alcohol citronellol and of geraniol/nerol. Its genuine claim to fame is as the dominant volatile behind citronella-oil repellency and the chemical starting point for PMD (para-menthane-3,8-diol), the registered “oil of lemon eucalyptus” repellent — but PMD is a cyclised derivative whose strong, long-lasting efficacy must not be read back onto the aldehyde. Beyond that, its isolate evidence is thin and entirely preclinical: consistent in-vitro antifungal activity and rodent CNS/analgesic signals.

What the evidence supports
  • A real repellent building block: citronellal drives citronella-oil repellency and is the precursor to the registered repellent PMD — though free citronellal is volatile and short-lived on skin 9Reference 92006Adult repellency and larvicidal activity of five plant essential oils against mosquitoesView study →.
  • The honest headline: no human trials of the isolate; antifungal MICs are high, the rodent sedative/analgesic data use high i.p. doses, and PMD’s registered efficacy belongs to the derivative, not citronellal 3,7Reference 32017Insights into the intracellular mechanisms of citronellal in Candida albicans (ROS-mediated necrosis, mitochondrial dysfunction, DNA damage)View study →Reference 72025AnimalCitronellal exerts sedative-like effects and augments diazepam’s action in Swiss mice, possibly through the GABAergic pathwayView study →.
Evidence by indicationStrength of support
Insect Repellent / LarvicidalShaky
30%
Antifungal / AntimicrobialShaky
26%
Sedative / Anxiolytic / AnticonvulsantShaky
24%
Anti-Inflammatory / AnalgesicShaky
20%
1. Insect repellent / larvicidal

Citronellal is a major constituent behind citronella-oil repellency and appears in larvicidal essential-oil screens 9Reference 92006Adult repellency and larvicidal activity of five plant essential oils against mosquitoesView study →; it is the industrial precursor to PMD, the registered lemon-eucalyptus repellent.

Gap: almost all field/efficacy data are whole-oil or PMD, not isolated citronellal — free citronellal is volatile and short-lived on skin (precisely why industry cyclises it to the longer-lasting PMD), so do not credit PMD’s registered efficacy to the aldehyde 9Reference 92006Adult repellency and larvicidal activity of five plant essential oils against mosquitoesView study →.

2. Antifungal / antimicrobial

Citronellal shows a consistent membrane/ergosterol mechanism: in Penicillium digitatum it depletes ergosterol and downregulates ERG genes (especially ERG3) 4Reference 42021Citronellal exerts its antifungal activity by targeting ergosterol biosynthesis in Penicillium digitatumView study →, and in Candida albicans it drives ROS-mediated necrosis, mitochondrial depolarisation and DNA damage 3Reference 32017Insights into the intracellular mechanisms of citronellal in Candida albicans (ROS-mediated necrosis, mitochondrial dysfunction, DNA damage)View study →, with MIC ~256 µg/mL against clinical C. albicans 5Reference 52022The antifungal and antibiofilm activity of Cymbopogon nardus essential oil and citronellal on clinical strains of Candida albicansView study →.

Gap: MICs are high (weak potency versus drug antifungals), in-vitro only, with no in-vivo or clinical antifungal data 3,5Reference 32017Insights into the intracellular mechanisms of citronellal in Candida albicans (ROS-mediated necrosis, mitochondrial dysfunction, DNA damage)View study →Reference 52022The antifungal and antibiofilm activity of Cymbopogon nardus essential oil and citronellal on clinical strains of Candida albicansView study →.

3. Sedative / anxiolytic / anticonvulsant

In Swiss mice, citronellal prolongs barbiturate sleep and augments diazepam 7Reference 72025AnimalCitronellal exerts sedative-like effects and augments diazepam’s action in Swiss mice, possibly through the GABAergic pathwayView study →, is anxiolytic in standard mazes 8Reference 82025Anxiolytic-like effects of citronellal and phytol, possibly through the GABAergic interaction pathwayView study → and anticonvulsant 6Reference 62024Anticonvulsant effect of (±)-citronellal, possibly through GABAergic and voltage-gated sodium-channel pathwaysView study → — effects reversed or rationalised via GABA-A interaction, with a voltage-gated sodium-channel component for the anticonvulsant action 6Reference 62024Anticonvulsant effect of (±)-citronellal, possibly through GABAergic and voltage-gated sodium-channel pathwaysView study →.

Gap: entirely rodent plus in-silico docking, at high i.p. doses (50–250 mg/kg), with no human data and a GABAergic mechanism that is inferred (flumazenil-sensitivity + docking), not receptor-confirmed 6,7Reference 62024Anticonvulsant effect of (±)-citronellal, possibly through GABAergic and voltage-gated sodium-channel pathwaysView study →Reference 72025AnimalCitronellal exerts sedative-like effects and augments diazepam’s action in Swiss mice, possibly through the GABAergic pathwayView study →.

4. Anti-inflammatory / analgesic

Intraperitoneal citronellal reduces spontaneous activity, produces analgesia/sedation and attenuates mechanical/inflammatory nociception (implicating the NO–cGMP–ATP-sensitive-K⁺-channel pathway) 1,2Reference 1Melo MS et al. · 2010AnimalAntinociceptive effect of citronellal in miceView study →Reference 2Quintans-Júnior LJ et al. · 2013AnimalCitronellal, a monoterpene present in Java citronella oil, attenuates mechanical nociception response in miceView study →.

Gap: preclinical only, and overlapping heavily with the sedation signal (sedated animals under-respond), so analgesic specificity is uncertain 1,2Reference 1Melo MS et al. · 2010AnimalAntinociceptive effect of citronellal in miceView study →Reference 2Quintans-Júnior LJ et al. · 2013AnimalCitronellal, a monoterpene present in Java citronella oil, attenuates mechanical nociception response in miceView study →.

Mechanisms

Target / pathwayEffectRelevant to
Fungal ergosterol biosynthesis (↓ ERG genes; lanosterol accumulates)loss of membrane integrityantifungal
ROS → mitochondrial depolarisation → DNA damageoxidative fungal cell deathantifungal (C. albicans)
GABA-A receptor (flumazenil-reversible)sedation, anxiolysis, diazepam potentiationCNS depressant (rodent)
GABA-A + voltage-gated Na⁺ channel (docking-inferred)raised seizure thresholdanticonvulsant (rodent)
NO–cGMP–K⁺(ATP) channel pathwayperipheral/central antinociceptionanalgesia (rodent)

Insect-acetylcholinesterase inhibition is documented for the alcohol citronellol, not the aldehyde — omitted here to preserve isomer discipline.

Pharmacokinetics

There is no dedicated human pharmacokinetics. Citronellal is a small (C₁₀H₁₈O), lipophilic, volatile reactive aldehyde: expected to be rapidly absorbed but with low systemic persistence, quickly oxidised to citronellic acid (excreted as conjugates) or reduced to citronellol, with some cyclisation to PMD-type diols. Its reactivity toward skin proteins (Schiff-base/Michael chemistry) underlies its sensitiser behaviour rather than any circulating pool, and the high effective rodent doses are consistent with rapid clearance and low bioavailability.

Clinical trials

There are no clinical trials of isolated citronellal. Human and field data exist only for whole citronella oil and for the derivative PMD (a registered repellent) — neither substitutes for isolate evidence.

CompletedPlannedTerminatedPreclinical
—(none)——Modest

Last checked: July 2026.

Toxicity & Safety

Citronellal has low acute toxicity and a long history as a GRAS flavouring/fragrance ingredient, with wide margins in rodent acute-toxicity studies. The headline caveat is topical: it is a recognised fragrance contact allergen, and as a reactive aldehyde it is more irritant than its parent alcohols and readily autoxidises to sensitising hydroperoxides. Treat it as a topical irritant/sensitiser — dilute well, avoid oxidised material, and note that concentrated leave-on use is the main risk under EU fragrance-allergen labelling.

Pregnancy & lactation

Trace dietary/aromatic amounts fine; avoid concentrated or undiluted use. No reproductive-safety data exist for isolated citronellal; incidental culinary and aromatic exposure is not a concern, but concentrated/therapeutic or undiluted topical use is best avoided in pregnancy and lactation — a reactive aldehyde with no established safety margin.

Dosage

There is no established human therapeutic dose, and citronellal is not recommended as an isolated oral supplement. Real-world use is as a trace fragrance/flavour ingredient and, topically, only well-diluted within a carrier (aromatherapy/repellent blends, typically ≤1% for leave-on), with a patch test first. For durable repellency, the PMD derivative — not free citronellal — is the evidence-backed choice. All efficacy dosing to date is preclinical (rodent i.p. 50–250 mg/kg; antifungal MIC ~256 µg/mL) and not translatable to humans.

References

  1. Melo MS, et al. (2010). Antinociceptive effect of citronellal in mice. Pharmaceutical Biology. https://pubmed.ncbi.nlm.nih.gov/20645719/
  2. Quintans-Júnior LJ, et al. (2013). Citronellal, a monoterpene present in Java citronella oil, attenuates mechanical nociception response in mice. Pharmaceutical Biology. https://pubmed.ncbi.nlm.nih.gov/23795810/
  3. (2017). Insights into the intracellular mechanisms of citronellal in Candida albicans (ROS-mediated necrosis, mitochondrial dysfunction, DNA damage). Revista da Sociedade Brasileira de Medicina Tropical. https://pubmed.ncbi.nlm.nih.gov/28954074/
  4. (2021). Citronellal exerts its antifungal activity by targeting ergosterol biosynthesis in Penicillium digitatum. Journal of Fungi (Basel). https://pubmed.ncbi.nlm.nih.gov/34072578/
  5. (2022). The antifungal and antibiofilm activity of Cymbopogon nardus essential oil and citronellal on clinical strains of Candida albicans. Brazilian Journal of Microbiology. https://pubmed.ncbi.nlm.nih.gov/35386096/
  6. (2024). Anticonvulsant effect of (±)-citronellal, possibly through GABAergic and voltage-gated sodium-channel pathways. Neurochemistry International. https://pubmed.ncbi.nlm.nih.gov/38395152/
  7. (2025). Citronellal exerts sedative-like effects and augments diazepam’s action in Swiss mice, possibly through the GABAergic pathway. Brain and Behavior. https://pubmed.ncbi.nlm.nih.gov/40123142/
  8. (2025). Anxiolytic-like effects of citronellal and phytol, possibly through the GABAergic interaction pathway. Molecular Neurobiology. https://pubmed.ncbi.nlm.nih.gov/41261301/
  9. (2006). Adult repellency and larvicidal activity of five plant essential oils against mosquitoes. Journal of the American Mosquito Control Association. https://pubmed.ncbi.nlm.nih.gov/17067055/