Citronellol

Aroma and sensory profile

Citronellol is rose with the sweetness turned down and the wax turned up. Fragrance references type it floral with medium strength and describe it neat as floral, leather, waxy, rose bud, and citrus, or floral, rosy, and sweet citrus with green, fatty terpene nuances; its flavor at 20 parts per million is floral, rose, sweet, and green with fruity citrus nuances [1]. Against geraniol, the other rose alcohol, citronellol is fresher, waxier, and more petal than perfume, with a faint leathery or fatty edge that geraniol lacks.

The molecule, 3,7-dimethyloct-6-en-1-ol, has one stereocenter and is chiral. (−)-citronellol, the form of rose and geranium oils, is described as floral, rose, waxy, geranium oil, and powdery, with a substantivity of 56 hours on a blotter [2]. (+)-citronellol, the form of citronella oils, is described as citronella oil, rose, leaf, oily, and petal [3]. The (−) form is the finer rose; the (+) form is greener and more citronella. HSDB records that citronellol occurs in both enantiomeric forms, with rose and geranium the richest sources [4].

Effects and research

No human trial of citronellol was found. A 2019 systematic review of 32 papers found antibiotic and antifungal activity in vitro and analgesic and anticonvulsant activity in vivo, called it a promising molecule for future pharmacological study, and acknowledged the absence of human evidence [5]. The Research Institute for Fragrance Materials assessed the racemate in 2023 [8].

The cardiovascular result is the most specific. In rats, intravenous citronellol at 1 to 20 milligrams per kilogram produced dose-dependent hypotension and tachycardia, and in isolated mesenteric artery rings it relaxed contractions fully and antagonized calcium-induced contraction by 97 percent, a direct vascular smooth muscle effect [6]. In mice, intraperitoneal citronellol at 25 to 100 milligrams per kilogram reduced mechanical hyperalgesia induced by carrageenan, tumor necrosis factor alpha, prostaglandin E2, and dopamine, with reduced activation of spinal cord lamina I [7].

One inhalation result cuts against the aromatherapy reputation. Mice exposed to beta-citronellol vapor for 30 minutes showed increased anxiety-like behavior in the elevated plus maze and open field, with no change in memory or depression tests and no attraction or aversion to the odor itself; the authors advised caution with essential oils and cosmetics containing it [9]. It is one study, but it is the only inhalation behavioral study of citronellol found, and it did not find calm.

Natural sources

Citronellol is a rose, geranium, and citronella terpene. HSDB records it as widespread in nature in both enantiomeric forms, occurring in about 70 essential oils, with rose and geranium the richest sources [4], and the 2019 review adds the Cymbopogon grasses and Citrus species used in cooking and traditional medicine [5]. Fragrance databases note its isolation from geranium oil and lemon eucalyptus [1], place the (−) form in geranium oil, nutmeg, orange, apple juice, beer, bilberry, and black currant [2], and the (+) form in black cumin seed and across the citrus family [3]. In cannabis citronellol is a trace terpenoid, occasionally reported in floral chemotypes and more often absent.

Boiling point and vaporization

PubChem compiles citronellol's boiling point as 225 °C from the Joint FAO/WHO Expert Committee on Food Additives and 224 °C from the CRC Handbook, with the Merck Index giving 108 to 109 °C at 10 mmHg for the (−) form [4]; fragrance references list 225 °C at 760 mmHg and 105 °C at 15 mmHg [1]. This profile keeps 225 °C (437 °F), the JECFA value, which matches what the site already listed. That places citronellol just below geraniol in the heart-note band, and its 56-hour blotter substantivity [2] shows how slowly it leaves a surface. Its instability is oxidative: on air exposure it autoxidizes to hydroperoxides that are the main skin sensitizers in the aged material [10]. No thermal degradation study of citronellol was found.

Safety and regulation

Citronellol is listed by the US Food and Drug Administration as a permitted synthetic flavoring substance at 21 CFR 172.515, as "Citronellol; 3,7-dimethyl-6-octen-1-ol; d-citronellol" [12]. The Research Institute for Fragrance Materials assessed dl-citronellol in 2023 [8]. No cancer classification applies.

Its skin record follows the pattern of geraniol and linalool. Pure citronellol is a weak sensitizer; air-exposed citronellol loses concentration and gains potency, and hydroperoxides are its major oxidation products and main skin sensitizers [10]. In a series of 658 dermatitis patients, purified citronellol gave positive patch tests in 0.15 to 0.31 percent, oxidized citronellol in 0.61 to 4.5 percent [11]. Under Europe's classification inventory, 99.6 percent of notifications flag it as a skin sensitizer, 96 percent as a skin irritant, and 65 percent as a serious eye irritant [4], and it is among the fragrance allergens that must be declared on European cosmetic labels above threshold.

Industries and uses

Fragrance: citronellol is a foundation rose material in floral, rose, and geranium accords and one of the highest-volume fragrance alcohols, stocked as racemic and single-enantiomer grades [1][2][3]. Culinary: it holds FDA flavoring status and contributes rosy, green, fruity-citrus nuances at low parts-per-million levels [1][12]. Aromatherapy: rose, geranium, and citronella oils are its carriers; the oxidation and patch-test data, and the mouse anxiety result, are the relevant cautions [9][11]. Cosmetics: it is a declarable fragrance allergen in Europe, so formulators track its level and oxidation state [4][11].