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Compound Monograph

Limonene

Limonene — a citrus-scented monoterpene that is one of the most widespread plant volatile oils, valued for its fresh aroma and reported antimicrobial, antifungal, and hepatoprotective activity.

Work in progress

Classification

Limonene is a monoterpene, part of the terpenoids class. The largest class of plant compounds, built from five-carbon isoprene units — the essential-oil aromatics, resins, bitter principles, saponins, and plant sterols.

Terpenoids Monoterpenes

Where Does It Come From? (23)

Limonene is a naturally occurring monoterpene, found in Chaste Tree, Fennel, Buchu and 20 other sources. It is well tolerated orally (low toxicity).

Angelica Angelica archangelica Buchu Agathosma betulina Camu-camu Myrciaria dubia Cannabis Cannabis sativa/indica Caraway Cashew Anacardium occidentale Chaste Tree Vitex agnus-castus Chinese Skullcap Scutellaria baicalensis Citrus peel Cornflower Centaurea cyanus Dill Fennel Foeniculum vulgare Fish Mint Houttuynia cordata German Chamomile Matricaria chamomilla Hyssop Hyssopus officinalis Juniper Juniperus communis Lemongrass Cymbopogon citratus Mexican Tarragon Tagetes lucida Muira Puama Ptychopetalum olacoides Peppermint Mentha piperita Pine Pinus spp. Walnut Juglans nigra Yarrow Achillea millefolium

Research & Evidence

Limonene is one of the most common monoterpenes in nature and turns up across a wide range of the herbs in this database as a component of their volatile (essential) oils. It is the compound most responsible for fresh, citrus-like aromas, and on the source-herb pages it is discussed in three main ways:

  • Antifungal, antimicrobial & insect-repellent — in chaste tree (Vitex agnus-castus), the essential oils pinene, bornyl acetate, and limonene are described as anti-fungal, anti-microbial, and insect-repellent 1Reference 1Hoffman D · 2003Medical Herbalism: The Science and Practice of Herbal Medicine. This is the most clearly named activity for limonene in the database.
  • Hepatoprotective role — fennel (Foeniculum vulgare) seed essential oil provides potent hepatoprotective effects against carbon-tetrachloride-induced liver damage in rats, and its content of delta-limonene (together with beta-myrcene) is suggested to play a key role in this protection 2Reference 2H et al. · 2003Hepatoprotective effect of Foeniculum vulgare essential oil, Fitoterapia, vol.
  • A principal volatile-oil constituent — limonene is named as one of the main volatile oils of buchu (Agathosma betulina), alongside menthone and pulegone 3Reference 3Bone K · 2013Principles and Practice of Phytotherapy. It is also reported among the volatile leaf compounds of walnut (Juglans nigra) 4Reference 4Farag MA · 2008Headspace analysis of volatile compounds in leaves from the Juglandaceae (walnut) family, among the main plant chemicals of cashew (Anacardium occidentale) 5Reference 5Taylor · 2005The healing power of rainforest herbs: A guide to understanding and using herbal medicinals, and quantified at around 1.71% of the volatile oil of yarrow (Achillea millefolium) 6Reference 6Battaglia · 2003The Complete Guide to Aromatherapy (2nd ed.). It appears in smaller proportions in the essential oils of pine, German chamomile, and camu-camu.

This is a representative summary drawn from the source-herb monographs rather than an exhaustive review; the references below are the studies cited on those pages that genuinely pertain to limonene, and this section will grow as more compound-specific research is added.

Toxicity & Safety

Limonene is generally regarded as well tolerated and is widely consumed as a normal part of citrus-containing foods. As a volatile-oil terpene, its main practical caution is dose-dependent: concentrated essential oils high in limonene can irritate the skin and mucous membranes if applied undiluted, and oxidised limonene (old or poorly stored oil) is a more common skin sensitiser than fresh material. Used at the modest levels found in whole herbs and properly diluted preparations, it carries a low risk profile.

References

  1. Hoffman D. Medical Herbalism: The Science and Practice of Herbal Medicine. Rochester, VT: Healing Arts Press; 2003:62-120.
  2. H. Ozbek, S. Ugras, H. Dulger (2003). Hepatoprotective effect of Foeniculum vulgare essential oil, Fitoterapia, vol. 74, no. 3, pp. 317–319
  3. Bone K, Mills S. (2013). Principles and Practice of Phytotherapy. Elsevier health. China.
  4. Farag MA. (2008). Headspace analysis of volatile compounds in leaves from the Juglandaceae (walnut) family. J Essent Oil Res. 20(4):323–7.
  5. Taylor, L. (2005). The healing power of rainforest herbs: A guide to understanding and using herbal medicinals. Garden City Park, NY: Square One Publishers.
  6. Battaglia, S. (2003). The Complete Guide to Aromatherapy (2nd ed.). Brisbane, Australia: The International Centre of Holistic Aromatherapy. (Pg 276-277).