Linalool

Linalool is a volatile alcohol providing the floral scent of lavender, bergamot, and many other plants. Together with its ester linalyl acetate, it forms the major fraction of lavender essential oil [1]. In bergamot peel oil, the same pair accompanies limonene [2]. Food manufacturers purchase it as a flavoring agent. These two compounds are the main aroma constituents of Earl Grey tea [3]. Cosmetic and perfume manufacturers use it as a fragrance. Linalool and limonene are the two most frequently added fragrance substances in scented products [4]. The molecule also has a drawback: it oxidizes on air contact, and its oxidized form is a common contact allergen [5].

Where is it found in lavender and bergamot, and in what amounts?

In flowers, as essential oil. Lavender oil is obtained by steam distillation of flowering tops [6]. In a study comparing ten cultivars, true lavender (Lavandula angustifolia) yielded 2.8% to 5.0% oil from dry flowers. Lavandin (L. × intermedia, a hybrid of true lavender and spike lavender) yielded 7.1% to 9.9% [7]. In a lavandin grown in Isparta, oil yield was measured at approximately 1.2% from fresh flowers and 5.8% from dry flower heads [8].

More than half of the oil is linalool and linalyl acetate. In six true lavender cultivars and one lavandin cultivar from Western Anatolia, linalyl acetate was 29.1% to 46.9%, and linalool was 28.1% to 36.8%. In another lavandin cultivar, linalool reached 28.5% and 1,8-cineole reached 15.7%. In six true lavender cultivars, camphor was below 0.5% [1]. In 13 new cultivars bred in Ukraine, linalool ranged from 11.4% to 46.7%, and linalyl acetate ranged from 7.4% to 44.2% [9].

Three species, three profiles. True lavender, lavandin, and spike lavender (L. latifolia) may be sold under the same name but are not identical. In six spike lavender oils from Southern Spain, linalool was 27.2% to 43.1%, 1,8-cineole was 28.0% to 34.9%, and camphor was 10.8% to 23.2% [10]. In oil of the Lavandin Grosso cultivar, camphor was measured at 8.1% [7]. The name alone does not specify the ratio: in a true lavender oil from dry flowers, camphor was 6.6% to 9.2%, and in the same study, prolonged distillation reduced the 1,8-cineole share from 35% to 6.4% [11]. Ratios are determined by analytical measurement.

In the peel of bergamot. Bergamot (Citrus bergamia) oil is cold-pressed from the fruit peel [12], and its main components are linalyl acetate, limonene, and linalool [2].

Linalool, linalyl acetate, linalool oxide: what is the difference?

Values are taken from PubChem. XLogP indicates whether a substance is lipophilic or hydrophilic. Higher values indicate higher lipophilicity. Linalool is lipophilic at 2.7 but disperses slightly in water. Linalyl acetate is more lipophilic at 3.3. Linalool oxide is the most hydrophilic at 1.4.

Linalool has two enantiomers. Two molecules with the same formula are mirror images of each other (enantiomers). Linalool in lavender oil is the (R)-(−) enantiomer (CAS 126-91-0), whereas coriander oil contains the (S)-(+) enantiomer (CAS 126-90-9) [13]. Chemically synthesized linalool is a racemic mixture. In a commercial linalool sample, the (R) share was 50.9% and the (S) share was 49.1%. In the same study, sensory perception of this mixture was close to the (R) enantiomer [13]. The two enantiomers differ in odor threshold and odor quality [14]. In 24 subjects exposed to experimental stress, the (R) enantiomer was calming in heart rate measurements, while the (S) enantiomer acted as a stimulant on blood pressure and heart rate [15].

Linalyl acetate hydrolyzes back to linalool in water. Hot water and acid hydrolyze the ester bond. This begins during production: lavender extract obtained by supercritical CO₂ extraction contained 34.7% linalyl acetate, whereas steam-distilled oil contained 12.1%. Authors attribute the difference to hydrolysis during distillation [16]. It continues during use: only 1.9% of linalyl acetate transferred unchanged into the beverage during Earl Grey tea brewing [17]. In an acidic medium, linalool itself converts into a cyclic alcohol, alpha-terpineol [18], [19].

Linalool oxide indicates aging. Linalool dropped to approximately 80% within ten weeks of air exposure, forming other compounds. One primary product is a hydroperoxide, a reactive intermediate toward skin [4]. Linalyl acetate degrades via the same pathway [20]. Even commercial 97% linalool contained oxidized impurities such as linalool oxide [21]. Lavandulol is also considered among the main constituents of lavender oil [22].

What is it used for?

Food: flavoring. Linalyl acetate and linalool were consistently detected in 90 Earl Grey teas across ten EU countries. Loose teas contained higher levels than bagged teas, with linalyl acetate at 66% and linalool at 39% [3]. In tea leaves, linalyl acetate is about 1.8 times higher than linalool. During brewing, two-thirds of linalool transferred into the beverage, while only 1.9% of linalyl acetate transferred. Of the transferred linalyl acetate, 17.0% reached the cup as linalool and 19.9% as other transformation products. Consequently, in the brewed tea, linalool is about 26 times higher than linalyl acetate [17]. In hot aqueous products, the consumer drinks the alcohol rather than the ester. Lavender aroma for food was compared across three methods, and brief ultrasound extraction was reported as a ready aroma source for alcoholic beverages and confectionery [23].

Cosmetics and fragrance: scent. Linalool was found to be the most potent odorant among its oxygenated derivatives. It is perceived at a few nanograms per liter of air [24]. Essential oil from micropropagated lavender at 0.1% in an oil-in-water emulsion exhibited protective effects against microbial growth for three months. The same oil increased procollagen production in human skin cells [25]. Oils from four lavender species suppressed staphylococci on direct contact but not in the vapor phase. In this study, the magnitude of the effect was independent of oil composition [26]. In another study, two lavender oils showed different effects on facial skin bacteria, with the oil containing 10% higher linalool and linalyl acetate being more effective [22].

Room scents and aromatherapy products. A review compiling 65 randomized controlled trials (7,993 participants) investigating lavender on anxiety reported significantly reduced anxiety scores in the inhalation subgroup (1,682 participants). No significant effect was found on systolic blood pressure [27]. Studies administered lavender oil inhalation, though most do not report the linalool content of the oil.

Essential oil, extract, or pure linalool: which form?

Essential oils are often sold diluted in an edible carrier oil. The certificate must state whether the percentage applies to the pure oil or the diluted product.

Why choose lavender or bergamot over pure linalool? Pure linalool provides a single compound and contains a racemic mixture [13]. Botanical oil provides three advantages. First, single enantiomer purity: lavender linalool is the (R) enantiomer [13], and enantiomers differ in scent, odor threshold, and physiological effects [14], [15]. Second, the full matrix: lavender oil provides linalyl acetate and lavandulol alongside linalool [1], [22]. Bergamot oil provides limonene and its own ester [2]. Third, verifiable origin: the enantiomeric distribution of linalool and linalyl acetate serves as an authenticity test [29], [7].

The choice depends on four questions.

• Which profile is required? For high camphor and 1,8-cineole, choose lavandin or spike lavender [7], [10]. For a profile dominated by linalool and linalyl acetate, choose true lavender [1]. For a limonene-dominated profile, choose bergamot [2].
• Is the product aqueous or heated? In hot aqueous processing, linalyl acetate does not pass unchanged; the fraction that transfers consists of linalool and other degradation products [17]. If an ester aroma is desired, select anhydrous or cold applications. Essential oil is insoluble in water and must enter aqueous systems via emulsion or carrier.
• How much is required? Adding 1 kg lavender oil to 1 ton cream (0.1%) with an oil containing 28% linalool yields 280 mg/kg linalool. With 37% linalool, it yields 370 mg/kg. The range is taken from a Turkish study [1]. These values are examples.
• Price. Price per kilogram of oil should not be compared in isolation. Lavandin and true lavender oils contain comparable linalool per kilogram, 34.0% [8] versus 28.1% to 36.8% [1]. The difference lies in the profile. Determine the required profile first, then compare prices accordingly. Global trade in lavandin oil is five times that of true lavender oil, though the most sought-after oil originates from true lavender [30].

How to read the certificate of analysis?

Method. Essential oils are analyzed by gas chromatography (GC), which separates the volatile mixture into components to quantify each share. Components are identified by mass spectrometry. Percentages on certificates are often area normalizations representing relative component ratios. In an oil diluted with vegetable oil, these relative shares do not change. Dilution is detected only by absolute quantification, such as milligrams per gram of oil [31]. The certificate must state the analytical method and the basis of the reported percentage.

What standard ranges do and do not indicate. The European Pharmacopoeia and ISO 3515 standard specify component ranges for lavender oil. None of the 13 newly bred authentic cultivars fell within these standard ranges. The reason was elevated alpha-terpineol (0.5% to 4.5%) and terpinen-4-ol (1.2% to 18.7%) [9]. Compliance with standard ranges does not prove authenticity, nor does non-compliance prove adulteration. These require separate testing.

Enantiomeric distribution. The ratio of (R) to (S) enantiomers in linalool and linalyl acetate is measured using a chiral GC column and serves as an authenticity test [29], [7]. Reconstituted oil added to bergamot oil is detected via the same ratio [32]. Under certain processing conditions, linalool partially racemizes toward equal enantiomeric proportions [29]. Results must be evaluated alongside processing history.

How adulteration appears. Common adulteration includes adding cheaper oils, adding synthetic compounds, and diluting with vegetable oils [31]. Adulteration of lavender oil with eucalyptus and rosemary oils has been reported [33]. A study analyzing 72 lavender oils identified 14 marker compounds and one synthetic additive marker, separating all authentic oils from counterfeit and inferior samples via a quality index [34].

Specifications differ from test results. A specification represents manufacturer limits. The measured value is the result for that specific lot. A technical data sheet (TDS) is a general document, whereas a certificate of analysis (CoA) belongs to an individual lot.

What indicates quality?

Low camphor and 1,8-cineole levels. In six true lavender cultivars, camphor was measured below 0.5% [1]. In lavandin and spike lavender oils, camphor reached up to 8.1% and 23.2%, and 1,8-cineole reached up to 34.9% [7], [10]. High values indicate incorrect species or adulteration.

Freshness. Terpenes in lavender oil oxidize at the same rate as pure isolated components. The oil lacks natural antioxidant protection [35]. The linalool oxide line, test date, and container fill level on the certificate must therefore be evaluated together.

Solvent residues. Concretes and absolutes are extracted using hexane and ethanol [8]. Distillation and supercritical CO₂ extraction use no organic solvents. Residues depend on the solvent used and must be reported on the certificate. Pesticide and heavy metal test results should also be requested for botanical raw materials.

How does it behave in formulations?

Air. Lavender oil oxidizes upon air contact at the same rate as its pure components, forming identical oxidation products and increasing sensitization capacity accordingly [35]. Pure linalyl acetate was a weak sensitizer, but after ten weeks of air contact, the concentration required for a reaction dropped from 25% to 3.6% [20]. Open or partially filled containers accelerate oxidation. Store in sealed, full containers in a cool, dark place. Use opened containers promptly. Encapsulation with cyclodextrin reduced the volatility of linalool and camphor, forming stable inclusion complexes [36].

Water, heat, and acid. In hot water, linalyl acetate converts to linalool and other products [17]. In acid, linalool converts to alpha-terpineol [18], [19]. In hot aqueous processing, the aroma profile shifts from ester notes to alcohol notes. Anhydrous and cold applications preserve the ester.

Skin: pure linalool is weak, oxidized linalool is a potent allergen. Pure linalool is non-allergenic or a very weak allergen [5]. Commercial 97% linalool was a weak sensitizer. Purifying impurities significantly reduced sensitization, though not entirely [21]. Oxidized linalool is a distinct compound. In six countries, 6.9% (3% to 13%) of 2,900 dermatitis patients reacted in patch testing [5]. Oxidized lavender oil itself yielded one of the highest reaction rates among tested essential oils at 2.8% [37]. Reactions occur even at low concentrations: among six sensitized individuals, five developed eczema from cream containing 3% oxidized linalool, and two reacted to 0.3% [38]. For formulators, the conclusion is clear. Preventing oxidation prevents allergen load. Ingredient labeling depends on product classification and applicable regulations.

Safety assessment. A safety assessment of linalool as a fragrance ingredient found current use levels acceptable [39]. Reports of hormone-like activity associated with lavender products were evaluated using modern guideline testing. In vitro assays of linalool and linalyl acetate, as well as in vivo and reproductive assays of linalool, showed no estrogenic or androgenic activity. Authors report that initial concerns in the literature were not substantiated [40].

Safety documentation. Follow the product safety data sheet (SDS) when handling extracts. Consult the SDS for transport and storage classifications.