Geraniol

Aroma and sensory profile

Geraniol is the smell most people mean by rose. Fragrance references type it floral with medium strength and describe it neat as sweet, floral, fruity, rose, waxy, and citrus; at 2 percent it is floral, sweet, rosy, fruity, and citronella-like with a citrus nuance, and its flavor at 3 parts per million is floral, rosy, waxy, and perfumey with a fruity, peach-like nuance [1]. Chemical handbooks compiled by PubChem agree: a sweet rose odor, a pleasant geranium-like odor [2]. Against linalool, the other great floral alcohol, geraniol is warmer, sweeter, and more obviously rose, where linalool is cooler and more lavender.

The molecule, (E)-3,7-dimethylocta-2,6-dien-1-ol, has no stereocenter, so there are no enantiomers to compare. Its geometric isomer, the (Z) form, has its own name, nerol, and a fresher, greener, less sweet rose character; the two occur together in rose and palmarosa and are routinely blended in perfumery. Geraniol also sits one oxidation step from geranial and neral, the two aldehydes that make up citral, which is why an old bottle of geraniol drifts toward lemon.

Effects and research

No human trial of geraniol was found. A 2019 review of the 2012 to 2018 literature listed antitumor, anti-inflammatory, antioxidant, antimicrobial, hepatoprotective, cardioprotective, and neuroprotective activities across experimental models and concluded that clinical evidence remains limited [3].

The mood and sedation data are rodent. In mice under chronic unpredictable mild stress, three weeks of geraniol restored sucrose preference and shortened immobility in the forced swim and tail suspension tests, with inhibition of nuclear factor kappa B and the NLRP3 inflammasome proposed as the mechanism [4]. Inhaled geraniol reduced spontaneous motor activity in mice, with a biphasic, W-shaped dose-response peaking at 4 × 10⁻⁴ and 4 × 10⁻² milligrams per cage, unlike the monotonic curves of menthol and camphor [5]. In rats, oral geraniol at 25 to 100 milligrams per kilogram reversed ketamine-induced hyperlocomotion and cognitive impairment and restored brain glutathione, superoxide dismutase, and catalase [6].

One pharmacokinetic result frames all of this. After an oral dose of 200 milligrams per kilogram in mice, the peak blood level of geraniol itself was only 0.05 micrograms per milliliter at one hour; geranic acid and glucuronide conjugates were the dominant forms in blood and tissue [7]. Whatever geraniol does in these models, it probably does through its metabolites, and inhaled exposures deliver far less than any oral dose above.

Natural sources

Geraniol is a plant volatile of flowers and fruits that occurs in nearly all terpene-containing essential oils. Palmarosa oil contains 70 to 85 percent geraniol, and geranium and rose oils carry large quantities; Fenaroli's handbook reports it in more than 160 essential oils including ginger grass, lemongrass, citronella, jasmine, lavender, bergamot, lemon, and orange, with palmarosa and Cymbopogon winterianus oils reaching roughly 80 to 95 percent [2]. Fragrance databases add rose oils, citronella, and palmarosa extracts as the commercial sources [1]. In cannabis it is a trace terpene, rarely reported above a few hundredths of a percent, and the rose note in a flower sample is more often geraniol's ester relatives than geraniol itself.

Boiling point and vaporization

PubChem compiles geraniol's boiling point as 230 °C from the Joint FAO/WHO Expert Committee on Food Additives and from Hawley's dictionary, 446 °F at 760 mmHg from the National Toxicology Program, and 229 to 230 °C from fragrance references [2]. This profile uses 230 °C (446 °F). That places geraniol well above linalool and just above citronellol, in the heart-note band: it does not flash off a warm hand the way limonene does, and it persists on skin and paper for hours. In a still, it is taken at reduced pressure, 111 to 112 °C at 10 mmHg [1]. Its instability is oxidative rather than thermal: air exposure converts it to geranial, neral, and a hydroperoxide [8], which matters more for safety than for scent.

Safety and regulation

Geraniol is generally recognized as safe as a synthetic flavoring substance at 21 CFR 182.60, as "Geraniol (3,7-dimethyl-2,6 and 3,6-octadien-1-ol)" [9]. The Research Institute for Fragrance Materials found it not genotoxic and set a no-expected-sensitization-induction level of 11,000 micrograms per square centimeter [10].

Pure geraniol is a weak sensitizer; the problem is what it becomes. On air exposure geraniol autoxidizes to geranial, neral, and geraniol-7-hydroperoxide, and these products are the allergens [8]. In a Swedish multicentre series, pure geraniol at 6 percent gave 1 percent positive patch tests, oxidized geraniol at 6 percent gave 3 percent, and oxidized geraniol at 11 percent gave 8 percent [11]. Geraniol is a constituent of fragrance mix I and, in a German analysis, was the most frequent allergen of the mix in women and in retired patients [12]. Fresh geraniol on skin is a small risk; an aged rose-scented product is not.

Industries and uses

Fragrance: geraniol is a foundation rose material in floral, fruity, and citrus accords and one of the highest-volume fragrance alcohols [1]. Culinary: it holds GRAS flavoring status and contributes rosy, peach-like nuances at low parts-per-million levels [1][9]. Aromatherapy: palmarosa, rose, geranium, and citronella oils are its carriers; the oxidation and patch-test data above are the caution for topical use of aged oils [11]. Cosmetics: it is among the fragrance allergens that must be declared on European cosmetic labels above threshold, so formulators track its level and its oxidation state [8][12].