What is limonene?

Limonene is a monoterpene (C10H16) that gives lemon, orange and other citrus peels their fresh smell. It also occurs in hemp, cannabis, mint and juniper, and is widely used as a fragrance, flavouring and solvent. It has low toxicity, but oxidised limonene can sensitise skin. It is one of the terpenes in the hemp Formula Swiss grows in Switzerland.

The fresh fragrance of citrus fruits such as lemons, limes, oranges and grapefruits comes from a natural compound called limonene. Present in the oils of many plants, limonene is commonly used to bring a bright, fruity scent to perfumes, household cleaners and cosmetic products.

Limonene is one of the terpenes in the Cannabis sativa varieties we grow in Switzerland, indoors, outdoors and in greenhouses. How much of it ends up in a finished hemp extract depends on how the plant is dried and processed; at Formula Swiss we use CO₂ extraction only.

In this article, I will focus on limonene, what it looks like as a chemical, where it comes from, what it does in people and animals, and how it is used in different products. I will also explain why learning about limonene is important for those of us interested in cannabis, hemp and plant science.

Prefer watching over reading? This video covers the key points from the article:

Key takeaways

• Limonene is a widely occurring terpene known for its strong citrus aroma.
• It is found in the essential oils of citrus fruits and several other plants.
• Limonene is commonly used in fragrances, cleaning agents and cosmetics.
• It is one of the major terpenes present in certain cannabis strains.
• Interest in limonene has increased due to its potential functional properties.

What are terpenes?

Terpenes are a large group of organic compounds that occur naturally in many plants and even in some animals. They are most widely recognised for producing the diverse range of scents and aromas we associate with the natural world.

For instance, the crisp scent of pine trees is due to a terpene known as pinene, while the soothing fragrance of lavender comes from linalool.

Within plants, terpenes play different roles, such as drawing in pollinators or serving as a natural defence against predators. These aromatic elements shape the unique character of many botanicals, influencing not only their fragrance but also how they interact with their surroundings.

What are terpenes?

Brief overview of limonene

Limonene is one particular type of terpene that is commonly found in citrus fruits such as lemons, limes or oranges, but also occurs naturally in several other plant species such as juniper berries, celery, mint, fennel, thyme or cypress trees. It is a colourless liquid that has been used in various products for its characteristic citrus scent.

Limonene is found in cleaning products, deodorant, shampoo, air fresheners and even in flea and tick repellent for pets. Additionally, it is used as a flavouring agent for food and beverages.

Limonene is classified as a cyclic hydrocarbon, which means it contains both carbon and hydrogen atoms arranged in a ring structure. Its chemical formula is C10H16, which makes it easily soluble in oils or fats but not water.

Importance of studying limonene

Limonene is a naturally occurring compound widely recognised for its role in many commercial products, especially within the fragrance and cleaning sectors.

Its fresh scent and effective solvent qualities make it a common ingredient in different formulations, underscoring the importance of understanding its characteristics and practical uses.

Looking at the sources and extraction methods of limonene also carries environmental importance. The way it is obtained can affect sustainability efforts, encouraging further study into more environmentally conscious production approaches.

Research into limonene also adds to the broader study of terpenes as a group of compounds. By learning more about limonene’s properties, researchers can better understand how terpenes function in natural settings as well as in commercial applications, supporting progress across a range of industries.

Chemical structure and properties of limonene

Limonene is a naturally occurring terpene that belongs to the class of cyclic monoterpenes. Monoterpenes are a group of organic compounds that are commonly found in plants and have a characteristic chemical formula of C10H16.

They are composed of two isoprene units connected head-to-tail, and limonene has the molecular formula C10H16 with a molar mass of 136.24 g/mol. Limonene has one chiral centre, so its individual enantiomers are optically active and can rotate plane-polarised light.

According to research published in the journal Environmental Science & Technology Letters, limonene has two enantiomers, (R)-limonene and (S)-limonene, with the same chemical formula but different spatial arrangements of atoms. (R)-limonene dominates in citrus, while pine and other conifers emit more (S)-limonene; the ratio depends on the source.

Limonene is a clear liquid with a strong citrus aroma and taste. It has low solubility in water but dissolves readily in organic solvents such as ethanol or hexane.

Sources of limonene in nature

Limonene is found naturally in many plant species, including citrus fruits such as lemons and oranges, peppermint, rosemary, juniper berries, fennel seeds, coriander seeds and pine needles. It is most abundant in the essential oils extracted from citrus peels. In plants, limonene serves several functions, such as attracting pollinators or repelling herbivores.

A 2021 scientific study published in the Journal of Horticultural Sciences examined the antimicrobial activity of fruit-peel extracts and pure limonene in laboratory tests against selected bacterial and fungal strains. These were laboratory tests, not tests on people.

Extraction methods of limonene

Limonene-rich essential oils are obtained from citrus peels by methods such as cold pressing, steam distillation or solvent extraction. These oils contain a mixture of compounds; they are not necessarily purified limonene. Cold pressing mechanically releases oil from the peel, while steam distillation carries volatile compounds with steam before condensation and separation.

Solvent extraction relies on chemicals such as hexane to dissolve limonene and other aromatic compounds from the peel. The method chosen often depends on factors such as cost, yield and purity.

Cold pressing and steam distillation avoid added solvents, but a life-cycle study found that energy use during extraction and purification matters as much as the method.

Limonene can also be produced through chemical synthesis, and researchers have developed microbial routes using organisms such as yeasts or bacteria. Process research examines production, recovery and economic feasibility.

Limonene in cannabis

Beyond its aromatic signature, limonene plays a role in differentiating the sensory appeal of cannabis cultivars.

Aroma profile and sensory attributes

Limonene gives certain cannabis strains a distinctive citrus smell. It is often compared to lemon, orange or grapefruit. However, a citrus scent does not always mean that a strain contains a high level of limonene. Laboratory testing is needed to confirm this.

The scent of limonene can change based on the plant's genetics, how it is grown and how it is processed after harvest. These factors can affect how much limonene is in the final product and how its scent is experienced.

Interaction with other cannabis compounds

Limonene is one of many terpenes in cannabis. It may work together with cannabinoids and other plant compounds. This combination can change how the cannabis plant smells and feels.

The exact ways these compounds interact are still being studied. Further research is needed to understand how limonene works with other parts of the cannabis plant.

What is cannabis?

What does limonene do?

In plants, limonene repels insects and attracts pollinators. In people, d-limonene has low toxicity: it is approved as a food flavouring, and human studies with repeated doses for up to a year found no serious harm. The kidney tumours once seen in male rats occur through a mechanism that does not apply to humans (Sun, 2007).

In a small controlled study, inhaled d-limonene reduced the anxiety that THC caused in healthy adults (Spindle et al., 2024).

On skin, limonene that has oxidised in air can cause allergic reactions in sensitive people. That is why EU cosmetics must declare it on the label above 0.001% in leave-on products and 0.01% in rinse-off products.

For pets, concentrated d-limonene can be harmful: insecticidal dips with d-limonene caused drooling, unsteadiness, tremors and low body temperature in cats at higher concentrations (Hooser et al., 1986).

Industrial uses of limonene

Limonene is a highly adaptable compound used across many industries because of its fresh aroma and strong solvent properties. It is present in products ranging from household cleaners to personal care items, offering both functional and sensory value.

Fragrance ingredients in consumer products

Recognised for its bright citrus scent, limonene is a popular fragrance ingredient in a wide range of consumer goods. It is frequently added to perfumes, soaps and other personal care products, where it helps create pleasant sensory experiences. This natural compound is often chosen for the freshness it brings to everyday formulations.

Solvent for cleaning products

Limonene is also valued as a solvent in cleaning formulations because it can dissolve oils. It is used in products such as degreasers, furniture polishes and carpet cleaners. Being plant-derived does not automatically make it the greener choice.

Its use reflects growing interest in cleaning agents that balance strong performance with more sustainable practices.

Components in cosmetics and personal care products

In cosmetics and personal care formulations, limonene offers more than fragrance. It also helps ingredients blend smoothly, improving the overall texture and performance of products such as shampoos, lotions and bath items. This versatility enhances both the feel and aroma of these goods.

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