Limonene: properties, uses, pros, cons, safety
Limonene (4-isopropenyl-1-methylcyclohexene) is a monoterpene hydrocarbon, one of the most frequently found in the plant kingdom, synthesised naturally from plants through a process with geranyl pyrophosphate.
It has two optical isomers:
- d-limonene
- l-limonene, a slightly yellow transparent liquid with a pleasant lemon scent which is produced industrially by cold pressing of generally dried citrus pulp and peel or by mechanical vaporization processes such as Soxhlet.
Because of its olfactory characteristics and its wide availability in nature, it is a flavouring terpene that is included in beverages, foodstuffs, home cosmetics and personal hygiene products in order to impart a pleasant fragrance to the product.
Limonene is an organic compound found in the essential oils of citrus fruits, known for its fresh, citrus scent. It is commonly used as a fragrance in cosmetics, skin care products, and perfumes.
Chemical Composition and Structure
The chemical composition of Limonene includes:
- Structure: It is a monoterpene with the chemical formula C10H16, characterized by a cyclic structure that contributes to its aromatic properties.
Structurally, Limonene consists of a cyclic ring and an aliphatic chain, allowing effective interaction with olfactory receptors.
Physical Properties
Appearance: Typically a colorless or pale yellow liquid.
Solubility: Soluble in alcohol and oils; insoluble in water. It dissolves dammar and rosin. In the presence of inorganic acids, limonene reacts with water to form -terpinol and terpenediol hydrate.
pH: Neutral.
Odor: Fresh, citrusy, characteristic of citrus fruits.
Stability: Generally stable but sensitive to oxidation and light.
Production Process
Extraction: Limonene is extracted from citrus essential oils, such as lemon and orange, through distillation or cold pressing.
Purification: The product is purified to remove impurities and ensure quality.
Formulation: Purified Limonene is incorporated into various cosmetic and fragrance formulations.
Applications
Cosmetics: Commonly included in perfumes, lotions, and skin care products for its citrus scent.
INCI Functions:
Deodorant agent. When substances that give off an unpleasant odour are included in cosmetic formulations (typical examples are methyl mercaptan and hydrogen sulphide derived from garlic), deodorants attenuate or eliminate the unpleasant exhalation. It helps counteract the formation of bad odours on body surfaces.
Solvent. It is the substance for dissolving or dispersing surfactants, oils, dyes, flavourings, bactericidal preservatives in solution.In fact, it dissolves other components present in a cosmetic formulation. Solvents are generally liquid (aqueous and non-aqueous).
Perfuming. Unlike fragrance, which can also contain slightly less pleasant or characteristic odours, the term perfume indicates only very pleasant fragrances. Used for perfumes and aromatic raw materials.
Cosmetic safety
Restricted cosmetic ingredient as III/88 III/167 III/168 a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported:
The presence of the substance shall be indicated in the list of ingredients referred to in Article 19(1), point (g), when its concentration exceeds: — 0,001 % in leave-on products — 0,01 % in rinse-off products. The peroxide value for each substance shall be less than 20 mmoles/L (This limit applies to the substance and not to the finished cosmetic product).
Studies
Limonene has demonstrated a wide range of health benefits (1): has an anti-stress action (2), and recent studies have also focused on limonene as it could have a preventive anti-tumour action (3) due to its antioxidant activities, which act mainly on apoptosis induced by tumour regression (4). In this study, the antibacterial activity of d-limonene and its potentiating activity of different classes of antibiotics for Gram-positive and Gram-negative bacteria were positively evaluated (5).
Used as a natural solvent in the manufacture of oil and oil-based paints, synthetic resins, synthetic rubbers, metal drying agent and solvent.
Limonene is commonly used as a fragrance in cosmetics to pleasantly scent products containing it. It can be obtained from lemon, laurel, bergamot, kumquat, geranium and many other flowers. In cosmetic applications, as limonene is easily oxidised by contact with air, there is a risk of skin allergy (6).
Reading many cosmetic texts and reviews, limonene, like linalool, or linalool, are cited as dangerous components, but this is not the case. It is the oxidation of the product that can be potentially dangerous, not the component itself, as limonene, in cosmetics, is processed in a non-sterile way and in contact with components that can accelerate the oxidative process. This is why it is one of the chemicals that can cause allergies and why it is mandatory to write it on the label when its percentage exceeds a certain value. It is a component that is considered safe if it is not oxidised, so remember to close the cap of the package in which it is inserted tightly to prevent air from penetrating inside for a long time and causing oxidation not only of this, but also of any other oxidation-sensitive components.
Safety
Linalool and D-limonene are common fragrances that oxidise easily on exposure to air. The resulting linalool and D-limonene hydroperoxides have been shown to have high frequencies of positive patch test reactions in several European and international studies .... In this study, the frequency of positive patch test reactions to linalool hydroperoxides is 20% (19/96) and the frequency of positive reactions to D-limonene hydroperoxides is 8% (7/90). These high frequencies suggest that patch testing for linalool and limonene hydroperoxides should be performed in all patients with suspected fragrance allergy (7).
The most relevant studies on the subject have been selected with a summary of their contents:
Typical optimal characteristics of the commercial product d-limonene
| Appearance | Light Yellow Liquid |
| Boiling Point | 175.4±20.0 °C at 760 mmHg |
| Melting Point | -84--104 °C |
| Density D20g/cm3 | 0.841-0.860 |
| Index of Refraction | 1.472-1.485 |
| Flash Point | 42.8±0.0 °C |
| LogP | 4.45 |
| Vapour density | 4.7 |
| Vapour Pressure | 1.5±0.2 mmHg at 25°C |
| Content of Camphene ≤ | 1.0% |
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- Molecular Formula : C10H16
- Molecular Weight : 136.238 g/mol
- Exact Mass 136.125198
- CAS : 138-86-3 9003-73-0 65996-98-7 7705-14-8 5989-27-5 8008-56-8 8008-57-9 8028-38-4 0008008-57-9
- UNII GFD7C86Q1W
- EC Number: 227-815-6 205-341-0 266-034-5 231-732-0
- DSSTox Substance ID: DTXSID6028288 DTXSID2029612
- MDL number MFCD00062992
- PubChem Substance ID
- InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h4,10H,1,5-7H2,2-3H3
- InChl Key XMGQYMWWDOXHJM-UHFFFAOYSA-N
- SMILES CC1=CCC(CC1)C(=C)C
- IUPAC 1-methyl-4-prop-1-en-2-ylcyclohexene
- ChEBI 15384
- NSC 757069 21466 844
- RTECS GW6360000
- UN Number 2052
Synonyms :
- Dipentene
- Polylimonene
- Nesol
- Cyclohexene, 1-methyl-4-(1-methylethenyl)-, homopolymer
- 1-methyl-4-(prop-1-en-2-yl)cyclohex-1-ene
- p-Mentha-1,8-diene, polymers
- +)-p-Mentha-1,8-diene
- (+)-Carvene
- 4-Isopropenyl-1-methyl-1-cyclohexene
- EINECS 205-341-0
- EINECS 231-732-0
- MDL number: MFCD00062991
- PubChem Substance ID 329759707
