Geraniol

Pharmacology & Research

Geraniol is an acyclic monoterpene alcohol with a sweet, rose-like odour — the signature aroma of rose, geranium and palmarosa, and a high-volume flavour and fragrance ingredient. Two framing points. First, keep it distinct from its close relatives: geraniol is the trans (E) alcohol, while nerol is its cis isomer, citronellol the saturated analogue, geranial the aldehyde (part of citral) and geranyl acetate the ester — several source-herb notes actually report the ester, not free geraniol. Second, although geraniol is one of the better-studied dietary monoterpenes in preclinical chemoprevention, its human evidence is a single indication (IBS) and its pharmacokinetics are limiting — rapid oxidation to geranic acid, short residence, high volatility ^{4,5Reference 4Pavan B et al. · 2018Geraniol pharmacokinetics, bioavailability and its multiple effects on the liver antioxidant and xenobiotic-metabolising enzymesView study →Reference 52023Human metabolism and urinary elimination kinetics of the fragrance geraniol after oral dosageView study →}. Its most robust isolate data are antimicrobial/antifungal (a defined ergosterol-and-membrane mechanism) ^{9Reference 9Pereira Fde O et al. · 2015Antifungal activity of geraniol and citronellol against Trichophyton rubrum involves inhibition of ergosterol biosynthesisView study →} and a genuine role as an insect repellent ^{10Reference 10Müller GC et al. · 2009Efficacy of the botanical repellents geraniol, linalool and citronella against mosquitoesView study →}.

1. Antimicrobial / antifungal

Geraniol shows reproducible activity against dermatophytes (Trichophyton rubrum), Candida and food/skin bacteria, with a well-characterised mechanism: inhibition of ergosterol biosynthesis plus membrane permeabilisation ^{9Reference 9Pereira Fde O et al. · 2015Antifungal activity of geraniol and citronellol against Trichophyton rubrum involves inhibition of ergosterol biosynthesisView study →}, part of the broad monoterpene-alcohol antimicrobial profile ^{1Reference 1Mączka W et al. · 2020One hundred faces of geraniolView study →}.

Gap: in-vitro only, with modest potency relative to pharmaceutical agents, and volatility that limits any systemic use ^{9,1Reference 9Pereira Fde O et al. · 2015Antifungal activity of geraniol and citronellol against Trichophyton rubrum involves inhibition of ergosterol biosynthesisView study →Reference 1Mączka W et al. · 2020One hundred faces of geraniolView study →}.

2. Irritable bowel syndrome

The strongest human signal, and the only isolated-geraniol clinical endpoint. In a double-blind RCT of 56 IBS patients, a low-absorbable geraniol food supplement once daily for 4 weeks significantly reduced the IBS Symptom Severity Score versus placebo (195 vs 265; 52% vs 17% responders) ^{11Reference 112022RCTGeraniol treatment for irritable bowel syndrome: a double-blind randomised clinical trialView study →}, aligning mechanistically with its anti-inflammatory and gut-microbiota effects.

Gap: a single trial using a specific low-absorbable formulation (not a generic oral dose), and no replication ^{11Reference 112022RCTGeraniol treatment for irritable bowel syndrome: a double-blind randomised clinical trialView study →}.

3. Anti-inflammatory

Oral geraniol reduces DSS- and TNBS-induced colitis in rodents — lowering TNF-α, IL-1β, IL-6 and myeloperoxidase, inhibiting NF-κB and raising PPARγ ^{6,7Reference 6De Fazio L et al. · 2015AnimalOral administration of geraniol ameliorates acute experimental murine colitis by inhibiting pro-inflammatory cytokines and NF-κB signallingView study →Reference 7Medicherla K et al. · 2015Geraniol ameliorates TNBS-induced colitis: involvement of Wnt/β-catenin, p38 MAPK, NF-κB and PPARγ signalling pathwaysView study →}. This is mechanistically coherent and partly underlies the IBS rationale.

Gap: rodent-only for the inflammation endpoint, at doses (~100–250 mg/kg) far above dietary exposure ^{6,7Reference 6De Fazio L et al. · 2015AnimalOral administration of geraniol ameliorates acute experimental murine colitis by inhibiting pro-inflammatory cytokines and NF-κB signallingView study →Reference 7Medicherla K et al. · 2015Geraniol ameliorates TNBS-induced colitis: involvement of Wnt/β-catenin, p38 MAPK, NF-κB and PPARγ signalling pathwaysView study →}.

4. Anticancer (chemoprevention)

Geraniol is one of the more-studied dietary monoterpenes for chemoprevention, with activity across prostate, colon, liver, kidney, skin and breast models and cell-cycle arrest via CDK2 and cyclin downregulation ^{2,3Reference 2Cho M et al. · 2016ReviewThe antitumour effects of geraniol: modulation of cancer hallmark pathways (review)View study →Reference 3Duncan RE et al. · 2004Geraniol and β-ionone inhibit proliferation, cell-cycle progression and CDK2 activity in MCF-7 breast cancer cells independent of effects on HMG-CoA reductase activityView study →}.

Gap: entirely preclinical, often at supraphysiologic doses, and the “signature” HMG-CoA/mevalonate mechanism is not causally established — exogenous mevalonate fails to rescue growth, so the link is correlative ^{3Reference 3Duncan RE et al. · 2004Geraniol and β-ionone inhibit proliferation, cell-cycle progression and CDK2 activity in MCF-7 breast cancer cells independent of effects on HMG-CoA reductase activityView study →}. No human oncology data.

5. Metabolic / antidiabetic

In streptozotocin-diabetic rats, geraniol (100–400 mg/kg for 45 days) lowered glucose, improved insulin and carbohydrate-metabolising enzymes and preserved β-cell histology ^{8Reference 8Babu SN et al. · 2017AnimalGeraniol ameliorates hyperglycemia by attenuating key enzymes of carbohydrate metabolism in streptozotocin-induced diabetic ratsView study →}.

Gap: single-species preclinical work at high doses, with no human data ^{8Reference 8Babu SN et al. · 2017AnimalGeraniol ameliorates hyperglycemia by attenuating key enzymes of carbohydrate metabolism in streptozotocin-induced diabetic ratsView study →}.

6. Insect repellent (use)

This is a real-world use rather than a health claim: geraniol is a genuine commercial repellent, with 5% geraniol formulations giving ~85% repellency and outperforming citronella and linalool indoors and outdoors ^{10Reference 10Müller GC et al. · 2009Efficacy of the botanical repellents geraniol, linalool and citronella against mosquitoesView study →}.

Gap: shorter-lived than DEET, volatility-limited, mixed in some feeding assays — and it is itself a sensitiser ^{10Reference 10Müller GC et al. · 2009Efficacy of the botanical repellents geraniol, linalool and citronella against mosquitoesView study →}.

Mechanisms

Target / pathway	Effect	Relevant to
Fungal ergosterol biosynthesis + membrane	↓ ergosterol, membrane permeabilisation	antifungal/antimicrobial
NF-κB / IκBα	↓ TNF-α, IL-1β, IL-6	anti-inflammatory, colitis
Wnt/β-catenin, p38 MAPK, PPARγ	↓ inflammatory signalling; ↑ PPARγ	anti-inflammatory
CDK2 / cyclins D1, E, A	G1 arrest, antiproliferation	anticancer
HMG-CoA reductase / mevalonate	inhibits — correlative, not causal (no mevalonate rescue)	anticancer (disputed)

Pharmacokinetics

Geraniol is rapidly absorbed and rapidly cleared: in rats, whole-blood decline follows pseudo-first-order kinetics with a half-life of roughly 12.5 minutes after IV dosing ^{4Reference 4Pavan B et al. · 2018Geraniol pharmacokinetics, bioavailability and its multiple effects on the liver antioxidant and xenobiotic-metabolising enzymesView study →}. It is metabolised by allylic oxidation to acidic products — chiefly geranic acid, plus 8-carboxygeraniol, 3-hydroxycitronellic acid and Hildebrandt acid ^{4Reference 4Pavan B et al. · 2018Geraniol pharmacokinetics, bioavailability and its multiple effects on the liver antioxidant and xenobiotic-metabolising enzymesView study →}. Human data confirm this: after oral dosing, urinary metabolites are dominated by Hildebrandt acid (~34% of dose) and geranic acid (~13%), with metabolite half-lives of ~2–4 hours ^{5Reference 52023Human metabolism and urinary elimination kinetics of the fragrance geraniol after oral dosageView study →}. The net picture — short residence, extensive first-pass oxidation and conjugation, low sustained systemic exposure, compounded by high volatility — is the central caveat separating isolated-geraniol pharmacology from the high-dose preclinical results, and it is why the one oral clinical trial used a low-absorbable, sustained-delivery formulation.

Clinical trials

Human data on isolated geraniol are essentially one endpoint: the IBS RCT above ^{11Reference 112022RCTGeraniol treatment for irritable bowel syndrome: a double-blind randomised clinical trialView study →}. There are no human trials for the anticancer, antidiabetic or anti-inflammatory applications, which remain preclinical.

Last checked: July 2026.

Toxicity & Safety

Geraniol is an FDA/FEMA GRAS flavouring with a favourable systemic-toxicity profile — a JECFA group ADI of 0.5 mg/kg body weight/day and rodent NOAELs well above 200 mg/kg — so ingestion toxicity at flavouring levels is low. The headline safety issue is topical, not systemic: geraniol is a recognised fragrance contact allergen and one of the 26 fragrance allergens requiring individual EU labelling, causing allergic contact dermatitis in sensitised individuals. Critically, auto-oxidation on exposure to air, heat or light generates hydroperoxides that are markedly more sensitising than fresh geraniol — so aged essential oils carry more allergenic risk. Undiluted material also irritates skin and mucosa. Interactions are theoretical only: geraniol modulates hepatic xenobiotic-metabolising and antioxidant enzymes in rodents at high doses ^{4Reference 4Pavan B et al. · 2018Geraniol pharmacokinetics, bioavailability and its multiple effects on the liver antioxidant and xenobiotic-metabolising enzymesView study →}, a mechanistic basis for possible CYP interactions, with none documented at food or fragrance levels.

Dosage

There is no established oral supplemental dose for isolated geraniol, and nothing here is a recommendation. Food/flavouring use is bounded by the JECFA group ADI (0.5 mg/kg body weight/day); the one human trial used a low-absorbable geraniol supplement once daily for 4 weeks — a product-specific formulation, not a generic dose ^{11Reference 112022RCTGeraniol treatment for irritable bowel syndrome: a double-blind randomised clinical trialView study →}; and preclinical rodent efficacy used ~100–400 mg/kg orally, far above any dietary exposure ^{8Reference 8Babu SN et al. · 2017AnimalGeraniol ameliorates hyperglycemia by attenuating key enzymes of carbohydrate metabolism in streptozotocin-induced diabetic ratsView study →}. Repellent formulations are typically ~5% topical or vapour ^{10Reference 10Müller GC et al. · 2009Efficacy of the botanical repellents geraniol, linalool and citronella against mosquitoesView study →}.

References