Basil

Basil (Ocimum basilicum L.): A Comprehensive Reference

1. Identity and Botanical Classification

Nomenclature and Taxonomy

Ocimum basilicum L. (sweet basil) belongs to the family Lamiaceae, which includes about 200 species occurring in various botanic varieties and forms. There are more than 30 species of herbs and shrubs of Ocimum, with great variability encompassing morphology, flower color, growth habits, chemical composition, leaves, and stems. Common English synonyms include sweet basil, common basil, and garden basil. Basil is also known as St. Joseph's Wort. It is a member of the large mint family, known botanically as Ocimum basilicum.

The word "basil" comes from the Greek word "basilikon," meaning "royal." Ocimum basilicum is found in tropical and subtropical regions of Asia and Africa, and in Central and South America.

Chemotypes

Because the chemical composition of basil essential oil varies substantially by geographic origin and cultivar, researchers recognize several chemotypes. Principal chemical constituents used to differentiate chemotypes include 1,8-cineole, linalool, methyl chavicol (estragole), nerol, geraniol, geranial, methyl cinnamate, methyl eugenol, β-bourbonene, α-trans-bergamotene, germacrene-D, δ-cadinene, and epi-α-cadinol. Among European specimens analyzed in one study, the compound with the highest relative proportion was linalool (29.1–70.3%), while estragole dominated in one essential oil with a relative proportion of 45.2%; all essential oils tested corresponded to the European chemotype, which is characterized by a high content of linalool or a combination of linalool and estragole.

Common Preparations and Forms

Ocimum basilicum (sweet basil) is used world-wide in culinary preparations, perfumes, rituals, and religious ceremonies. As a dietary supplement or natural ingredient, basil appears in the following forms:

• Fresh leaves: the most common culinary and traditional medicinal form.
• Dried leaf powder: used in teas, encapsulated supplements, and herbal preparations.
• Hydro-distilled essential oil: hydro-distilled essential oil content ranges from 0.5% to 0.8% of the aerial parts, with maximum amounts observed in winter and minimum in summer.
• Aqueous and hydroalcoholic extracts: used in pharmacological studies and some commercial supplements.
• Seed mucilage: basil seed mucilage can be considered as a thickening, stabilizing, fat-substitute, texturizer, surface-active, and emulsifying hydrocolloid.
• Tinctures: basil tincture preparations contain on average 0.187% (w/w) total polyphenols (of which 0.0247% are flavonoids), with methyleugenol (0.0006%) and estragole (0.00005%) detectable in the additive.

Basil is "generally recognized as safe" (GRAS) as a food by the U.S. Food and Drug Administration when consumed as a culinary herb.

2. Traditional and Historical Use

Origins and Spread

Basil has been cultivated for over 5,000 years and has many culinary, cultural or ritualistic, and practical purposes. It was first cultivated in Asia and traveled to Africa and the Mediterranean along spice routes. It is thought to have been brought to ancient Greece by Alexander the Great, to England from India in the mid-1500s, and to the United States in the early 1600s.

The earliest known reference to basil stretches back 5,000 years to Indian Vedic texts. Ancient records from 907 A.D. indicate sweet basil in the Hunan region of China, where it was used medicinally.

Ancient Egypt

Approximately 4,000 years ago, basil was used by the Egyptians for embalming, and it was also referenced as a herbal medicine in the Ebers Papyrus of 1500 BC. As a botanical used in embalming bodies, it was found with the mummies of ancient Egypt. Perhaps because of its embalming usage, basil was also a symbol of mourning.

India and Ayurveda

Basil has found many uses as part of various traditional medicines. It was recognized since ancient times for its therapeutic properties in the Unani and Ayurvedic medical systems. In India, its uses were diverse and numerous in the remedies of multiple regions. For example, basil leaf and seed or even the whole plant were used for treating fever, cough, colds, or as a treatment for reducing high blood pressure or combating fungal infections. Basil was used as part of herbal preparations to treat dysmenorrhea by creating a milk concoction consumed once a day for seven days. Leaf juices were used for digestive disorders, such as diarrhea, dysentery, constipation, gastritis, and vomiting.

Named Tulsi (holy basil), the fragrant herb is cherished in India for its healing properties. For Hindus, Tulsi is an essential part of the worship of Vishnu. It should be noted that Tulsi refers primarily to Ocimum tenuiflorum (syn. Ocimum sanctum), a closely related but distinct species, whereas the present article focuses primarily on O. basilicum.

Ancient Greece, Rome, and the Mediterranean

Basil found its place in ancient Egypt, Greece, and Rome, where it was used medicinally for a variety of ailments. Over time, basil's culinary significance grew, and it became an integral ingredient in various cuisines, particularly in Mediterranean and Southeast Asian cooking. Basil has religious significance in the Greek Orthodox Church, where it is used to sprinkle holy water.

Traditional Chinese Medicine

Sweet basil is a food-related plant that is widely used in traditional Chinese medicine. Textual records from the Hunan region document its medicinal application from at least the 10th century CE.

Folk Medicine — Broad Ethnomedicinal Use

Basil has been traditionally used in the folk medicines of various cultures as a tonic, anthelmintic, diuretic, and antispasmodic, and as a treatment for upper respiratory tract infections. In folk medicine, basil is widely used to treat headaches, coughs, kidney disorders, and intestinal worms, and as an antispasmodic agent. Traditionally, its flowers and leaves have been used as antispasmodics, digestive tonics, galactagogues, and stomach tonics, and are also applied for the management of gastroenteritis, fever, nausea, insomnia, depression, migraine, gonorrhea, dysentery, chronic diarrhea, acne, anosmia, and insect and snake bites.

3. Key Phytochemical Constituents

Essential Oil Composition

The plant contains various phytochemical constituents, which mostly consist of linalool, eucalyptol, estragole, and eugenol. The exact profile varies markedly by chemotype, geographic origin, season, and cultivation method. Key volatile constituents identified across published analyses include:

• Linalool: linalool is the most abundant component in many specimens, ranging from 56.7–60.6% in seasonally collected samples.
• Estragole (methyl chavicol): in some specimens, methyl chavicol is the dominant compound, constituting up to 86% of the total essential oil composition.
• Methyl eugenol and methyl chavicol: in one Western Ghats (India) specimen, the major constituents were identified as methyl eugenol (39.3%) and methyl chavicol (38.3%), accounting for 98.6% of the total oil.
• Methyl cinnamate: in specimens from South India, the major constituents were methyl cinnamate (70.1%) and linalool (17.5%), suggesting the plant may belong to the methyl cinnamate and linalool chemotype.
• 1,8-Cineole (eucalyptol), eugenol, α-bergamotene, germacrene-D, camphor, β-elemene, τ-cadinol, δ-cadinene: documented in various analyses with contributions ranging from trace amounts to several percent of the total oil composition.

In molecular distillation fractions of sweet basil crude oil, the major constituents of the residue fraction were estragole (17.06%), methyl eugenol (11.35%), and linoleic acid (11.40%), while the distillate fraction primarily contained methyl eugenol (16.96%), α-cadinol (16.24%), and α-bergamotene (11.92%).

The extraction method and the qualitative and quantitative variation of the compounds are highly dependent on factors such as type of cultivar; date, place, and conditions of cultivation; and seasonal variation and harvest.

Phenolic Acids and Polyphenols

The main (>0.1%) individual polyphenols detected in basil include rosmarinic, caffeic, chicoric, and ferulic acids. Rosmarinic acid is the most represented phenolic acid in all types of extracts, reported to be the most represented phenolic acid in basil across multiple studies.

Phytochemical characterization of a polyphenolic fraction of basil by UPLC with a diode-array detector and mass spectrometry revealed a high concentration of caffeic acid derivatives, especially chicoric and rosmarinic acid.

Flavonoids and Other Polyphenols

Basil contains a wide range of natural products including polyphenols such as anthocyanins and flavonoids. Leaves contain flavonoids including salvigenin, rutin, and gallocatechin, as well as organic and phenolic acids; stems contain flavonoids (vicenin, salvigenin) and phenolic acids (rosmarinic acid, salvianolic acid). Purple varieties are characterized by the accumulation of anthocyanins in leaves and flowers. LC-ESI-MS/MS analysis of individual compounds has allowed the quantification of 17 (poly)phenolic acids and 18 flavonoids in leaves and flowers.

Additional secondary metabolites identified via UPLC-ITQD MS include rosmarinic acid, ursolic acid, nepetoidin A and B, salvigenin, and quercetin-3-O-rutinoside as flavonoids and phenolics.

Other Constituents

The EFSA Compendium of Botanicals reports as substances of potential concern for human and animal health the occurrence of 1,8-cineole (3.74%–16.7%), camphor (1.2%), eugenol (1.4%–10.3%), estragole (2.4%–16.5%), and methyleugenol (0.5%–1.6%) in the essential oil from the aerial parts of O. basilicum. Other publications have also reported the presence of thujones (0.001%–14.84%), safrole (0.1%), and coumarin (0.12%–0.37%) in essential oils and other preparations from the leaves of O. basilicum.

4. Mechanisms of Action

Antioxidant Mechanisms

The antioxidant activities of herbal extracts are mainly due to their capacity to be donors of hydrogen or electrons and to capture free radicals. These actions are attributed to basil's composition, which is rich in flavonoids and polyphenols as well as compounds such as rosmarinic acid (RA), all of which are well-known for their antioxidant properties.

A polyphenolic fraction of basil showed significant antioxidant activity in human normal colon epithelial cells and colorectal adenocarcinoma cells, as measured by DPPH and FRAP assays, the activation of SOD and CAT enzymes, and the reduction in MDA levels after oxidative stress induction.

Anti-Inflammatory Mechanisms

It was shown that O. basilicum crude methanolic extract down-regulated TNF-α, IL-1β, and IL-2, and suppressed the induction of inducible nitric oxide synthase (iNOS) and the subsequent production of nitric oxide (NO) in LPS-stimulated RAW 264.7 macrophages in a time-dependent manner. Fixed oil of O. basilicum also blocked both cyclooxygenase and lipoxygenase pathways of arachidonic acid metabolism.

One in vitro study found that basil plants enhanced with arachidonic acid elicitor had the greatest inhibitory effect against lipoxygenase (LOX) (EC50 = 1.67 mg FW mL⁻¹) and cyclooxygenase (COX) (EC50 = 0.31 mg FW mL⁻¹), with inhibitory efficacy showing positive correlation with increased content of rosmarinic, benzoic, and o-coumaric acids.

Antimicrobial Mechanisms

The therapeutic properties of basil are attributed primarily to its rich composition of bioactive compounds, which include monoterpenes, sesquiterpenes, phenylpropanoids, anthocyanins, and phenolic acids; the bioactive compounds in basil may promote antimicrobial activity by disrupting the permeability of microbial membranes.

Antidiabetic Mechanisms

Basil aqueous extract elicited a significant dose-dependent pattern of inhibition against rat intestinal sucrase (RIS; IC₅₀ = 36.72 mg/mL), rat intestinal maltase (RIM; IC₅₀ = 21.31 mg/mL), and porcine pancreatic α-amylase (PPA; IC₅₀ = 42.50 mg/mL). These findings indicate that basil may reduce postprandial blood glucose spikes by slowing carbohydrate digestion and absorption.

5. Scientific Evidence by Area of Use

5.1 Antimicrobial Activity

The antimicrobial properties of basil essential oil are among the most extensively studied in preclinical settings.

The oil was found to be active against Gram-positive and Gram-negative bacteria, and fungi, with minimal bactericidal concentration values in the range of 0.143 ± 0.031 to 0.572 ± 0.127 mg/mL, 0.781 ± 0.382 to 1.875 ± 0.684 mg/mL, and 0.312 ± 0.171 to 0.442 ± 0.207 mg/mL, respectively.

Evaluation of antimicrobial activity of essential oils and linalool, the most abundant component, against bacterial strains including Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pasteurella multocida, and pathogenic fungi including Aspergillus niger, Mucor mucedo, Fusarium solani, Botryodiplodia theobromae, and Rhizopus solani was assessed by disc diffusion method; results of antimicrobial assays indicated that all tested microorganisms were affected.

Antioxidant activity testing determined EC₅₀ values of 115.36 and 54.77 µg/mL by DPPH and ABTS assays, respectively; basil essential oil demonstrated significant antimicrobial effects against Gardnerella vaginalis, Fannyhessea vaginae, Chryseobacterium gleum, and Candida albicans, with inhibition zones of up to 25.88 mm and MIC values ranging from 31 to 500 µg/mL. Basil essential oil had no toxic effect on Lactobacillus crispatus or human dermal fibroblasts.

Seed essential oil showed potent antibacterial effects against Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus, Proteus mirabilis, and Pseudomonas aeruginosa, and antifungal effects against Candida albicans.

Evidence quality: Essential oils have been proposed as natural alternatives to antibiotics or for use in combination with antibiotics against multidrug-resistant bacteria; however, most results come from in vitro and in vivo studies, and very little is known about their use in clinical studies. No robust randomized controlled clinical trials in humans have established clinical efficacy for infectious disease treatment with basil preparations.

5.2 Antioxidant Activity

The extract of O. basilicum acts as an antioxidant and effectively reduces the effects of high oxidizing agents such as hydrogen peroxide. Studies on cultivars showed high polyphenolic production in Red Rubin, Holy Green, and Basil Genovese, with low amounts in Subja; antioxidant potential was found to be more potent in the purple-flowered plant than in its white-flowered type.

A recent study demonstrated that hydroalcoholic extract of basil leaves showed antioxidant activities, as measured by the DPPH, reducing power, H₂O₂ scavenging, and anti-lipid peroxidation assays, with variable IC₅₀ values depending on the specific in vitro method used.

Evidence quality: Antioxidant effects are well-established in vitro and in cell-based models. Among essential oils, basil showed a moderate antioxidant activity in comparative analyses. Human clinical data on antioxidant outcomes specifically attributable to O. basilicum supplementation remain limited.

5.3 Anti-Inflammatory Activity

An in vitro study demonstrated that ethanolic leaf and leaf callus extracts significantly reduced nitric oxide as a pro-inflammatory mediator with concentrations of 0.01–1 mg/mL on RAW 264.7 macrophage cells.

A rat model study examining basil extract's immunomodulatory effects in an ovalbumin-induced asthma model found: a significant increase in IL-4, IgE, PLA₂, and total protein levels, as well as significant lung pathological indices, in asthmatic compared to control rats (P < 0.05 to P < 0.001), and treatment with O. basilicum extract modulated these parameters.

In a further study using sensitized ovalbumin rats, groups received drinking water containing three concentrations of O. basilicum (0.75, 1.5, and 3.0 mg/mL), three concentrations of rosmarinic acid (0.125, 0.25, and 0.5 mg/mL), and dexamethasone (1.25 μg/mL).

Evidence quality: Anti-inflammatory evidence is robust in preclinical models (cell culture and rodent), with multiple confirmed mechanisms. Human clinical trials specifically evaluating O. basilicum for inflammatory conditions remain absent in the peer-reviewed literature reviewed.

5.4 Antidiabetic and Metabolic Effects

Findings from systematic reviews reveal that specific plant extracts including Ocimum basilicum demonstrate potential in managing hyperglycemia through diverse mechanisms such as inhibiting α-glucosidase activity, enhancing insulin sensitivity, and providing antioxidant protection.

In animal models: treatment with 100 and 200 mg/kg extract significantly (P < 0.05) reduced fasting blood glucose concentration and slightly increased mean body weight in treated groups. Histopathological results revealed reconstitution of pancreatic islets towards normal cellular architecture in rats treated with aqueous extract of basil seeds, suggesting antidiabetic potential in streptozotocin-induced diabetes in rats.

Results of 20 RCTs analyzed in one systematic review provide evidence for the use of Ocimum basilicum as an adjunct therapy for diabetes and cardiovascular diseases, with improvements in glycemic control, lipid profiles, and oxidative stress markers. However, basil may be less potent than pharmaceutical options, and is therefore more likely to be used as a complementary therapy rather than as a stand-alone treatment.

Glucose-lowering and antioxidant effects of O. basilicum were observed biochemically in one animal study, with potential renoprotection against diabetes-induced nephropathy; further exploration of the mechanism and assessment of efficacy in humans through clinical study was recommended by the authors.

Evidence quality: Preclinical (animal and in vitro) evidence is moderate to strong for blood glucose lowering and enzyme inhibition. Human clinical evidence from RCTs exists but is generally modest in scale, and large, well-controlled clinical trials are still needed to confirm safety and optimal dosing in human patients.

5.5 Neuroprotective and Neurological Effects

Basil (Ocimum spp.) has been recognized for its therapeutic potential, and numerous studies have reported neuroprotective effects. It contains essential oils, flavonoids, and phenolic compounds contributing to antioxidant and anti-inflammatory properties, which have been associated with potential neuroprotective, hepatoprotective, antimicrobial, and immunomodulatory effects.

Long-term supplementation of chow with sweet basil (Ocimum basilicum) leaves improved memory performance of female aged mice in the novel object recognition test, and its hydroethanolic extract administered for 8 weeks by oral gavage was found to improve learning and memory impairment in male aged rats.

O. basilicum extract reversed maternal separation stress-induced increases in TNF-α and IL-1β expression in the hippocampus; additionally, its hydroethanolic extract administered for 8 weeks reversed aging-induced effects on interleukin-6 (IL-6) levels in the hippocampus and cortex of aged rats.

Ocimum basilicum has been described to have antidepressant and anxiolytic activities in preclinical models, although the relationship between the main olfactory bulb and depression and the chronic stress-induced dysfunction of the olfactory bulb requires further study. In a mouse study examining inhalation of O. basilicum essential oil, treatment significantly down-regulated caspase-3 gene expression (indicating reduced apoptosis) and up-regulated Ki67 gene expression (indicating enhanced neurogenesis) in the main olfactory bulb, while treated mice showed improved olfactory bulb mitral cell layer distortion induced by chronic unpredictable mild stress.

Evidence quality: Neuroprotective and mood-related evidence is entirely preclinical (rodent models), relying on animal behavioral tests and histopathological assessments. No human clinical trials for cognitive, mood, or neuroprotective outcomes have been conducted with O. basilicum specifically.

5.6 Anticancer Activity

Antioxidants and other bioactive compounds in basil leaves show anticancer potential; at a dosage of 4 mg/mL as aqueous extract, or essential oil up to 200 µg/mL, they could slow tumor growth and progression with regard to cell death and viability inhibition, and at dosages from 50 to 500 µg/mL, effective anti-proliferative activities have been observed.

O. basilicum seed essential oil showed anticancer activity against Hep3B cells (IC₅₀ 56.23 ± 1.32 µg/mL) and MCF-7 cells (IC₅₀ 80.35 ± 1.17 µg/mL) when compared with the positive control doxorubicin.

In vitro cytotoxicity screening of basil essential oil against the human cervical cancer cell line (HeLa), human laryngeal epithelial carcinoma cell line (HEp-2), and NIH 3T3 mouse embryonic fibroblasts using a methyl thiazol tetrazolium assay yielded IC₅₀ values of 90.5 and 96.3 µg/mL, respectively, with results revealing that basil oil has cytotoxic potential.

A single pure compound or a combination of compounds exhibits exceptional medicinal properties, including antiviral activity against both DNA and RNA viruses, antibacterial effects against both Gram-positive and Gram-negative bacteria, antifungal properties, antioxidant activity, antidiabetic potential, neuroprotective qualities, and anticancer properties.

Evidence quality: Anticancer data for O. basilicum are exclusively in vitro and in animal models. Based on 16 published studies, basil demonstrates anticancer activities in in vivo and in vitro models and could act as a potential cancer preventive agent. No human clinical trials for cancer prevention or treatment have been published.

5.7 Respiratory and Immunomodulatory Effects

The immunomodulatory and anti-inflammatory effects of hydro-ethanolic extract of Ocimum basilicum leaves were examined in ovalbumin-sensitized animals; Wistar rats were divided into groups and treated with O. basilicum extract at 0.75, 1.50, and 3.00 mg/mL in drinking water for 21 days; the levels of IL-4, IFN-γ, IgE, phospholipase A₂, and total protein in bronchoalveolar lavage fluid, and lung pathological changes were examined.

Evidence quality: Immunomodulatory and respiratory effects are supported only by animal model studies. Human clinical evidence in respiratory disease (e.g., asthma) is absent.

6. Body Systems and Health Areas

• Digestive system: Traditionally used for treatment of headaches, coughs, diarrhea, constipation, warts, worms, and kidney malfunctions.
• Cardiovascular and metabolic system: O. basilicum has been reported to exert cardiovascular benefits, including hypoglycemic, hypolipidemic, and anticoagulant effects through inhibition of platelet aggregation.
• Immune system: Due to its polyphenolic and flavonoidic content, O. basilicum can be considered an important ingredient in healthy diets; preparations may be effective as chemopreventive agents or adjunctive therapy in the treatment of different clinical conditions.
• Nervous system: Traditional medicine has used basil to alleviate brain disorders, digestive issues, respiratory problems, and stress-related conditions.
• Skin and antimicrobial: In one case report, a 2% formulation (20 mg/g weight/weight) of ethanolic basil extract in white petroleum jelly was applied topically; the papilloma began to regress and eventually disappeared between days 7 and 21, with skin texture progressively returning to normal; the antiviral activity may be due to phenolic, flavonoid, tannin, and alkaloid compounds found in it.
• Renal system: O. basilicum could protect the kidney against diabetes-induced nephropathy as revealed biochemically and histopathologically in animal models.

7. Dosage Forms and Dosages Reported in Studies

Reported dosages in the scientific literature vary considerably by preparation type, target condition, and study population. The following are dosages documented in specific studies:

• Aqueous/hydroalcoholic extract, oral animal studies: treatment with 100 and 200 mg/kg body weight extract significantly reduced fasting blood glucose concentration in treated groups.
• Basil extract in drinking water (immunological rat models): concentrations of 0.75, 1.5, and 3.0 mg/mL in drinking water were used for O. basilicum extract; rosmarinic acid concentrations of 0.125, 0.25, and 0.5 mg/mL were also tested.
• Topical formulation: a 2% formulation with 20 mg/g weight-per-weight (w/w) of ethanolic extract and white petroleum jelly was used as an ointment base in one clinical observation.
• Holy basil (Ocimum tenuiflorum) human RCTs (noted for comparison): anti-stress benefits have been identified in adults experiencing stress and generalized anxiety disorder at daily doses of 1,000 and 1,200 mg, respectively, in clinical trials.
• Essential oil yield: hydro-distilled essential oil content ranged from 0.5% to 0.8% of the dried aerial parts across seasonal samples.
• Anticancer — in vitro and human observations: human studies show effects at dosages from 1 to 2.5 mg/daily on general vital activities and on reducing cytokine activity.

No standardized, universally accepted clinical dosage range for O. basilicum supplements in humans has been established in regulatory pharmacopoeias or major institutional health body guidance reviewed.

8. Safety Considerations

Estragole (Methyl Chavicol) — Genotoxic and Carcinogenic Concerns

The content of estragole (methyl chavicol), a compound associated with potential risk to human health, was determined in essential oils of 12 basil herb samples; essential oils contained estragole at various levels, from 1.85 to 561.01 mg/mL. Estragole was shown to be genotoxic in vitro and in vivo, causing the formation of liver tumors in rodents. Owing to this experimental evidence, estragole was classified as a genotoxic carcinogen by the Scientific Committee on Food (SCF). Consistent with this classification, the Committee on Herbal Medicinal Products (HMPC) of the European Medicines Agency (EMA) concluded that estragole is a genotoxic carcinogen in rodents.

Humans are exposed to estragole through the diet and phytomedicines; after its absorption, it undergoes metabolic activation by CYP1A2 and SULT1A1 in the liver, which can give rise to DNA adducts and hepatocarcinogenesis.

However, the risk from normal culinary use may be substantially modulated by co-occurring compounds: it has been demonstrated that formation of DNA adducts by 1′-hydroxyestragole could be inhibited by basil extract, confirmed in intact human hepatoma cells, suggesting the likelihood that bioactivation and carcinogenicity may be much lower when estragole is administered at low doses and in a natural matrix.

Given the recommendation for limiting human exposure to estragole, the safety of some essential oils may be of concern due to their high levels of estragole content; results indicate the importance of chemical analysis of basil herb samples and the selection of chemotypes with low estragole content.

Safety concerns have been raised about promutagens and procarcinogens alkenylbenzenes contained in O. basilicum; however, a critical review concluded that due to polyphenolic and flavonoidic content, OB can be considered an important ingredient in healthy diets, and from a toxicological perspective, since the tumorigenic potential of alkenylbenzenes is counteracted by other OB constituents such as nevadensin.

Methyl Eugenol

The EFSA Compendium of Botanicals reports methyleugenol (0.5%–1.6%) in the essential oil from the aerial parts of O. basilicum as a substance of potential concern for human and animal health. Methyl eugenol is classified as a genotoxic carcinogen in rodent bioassays and shares a similar metabolic activation pathway with estragole.

EFSA Margin of Exposure Assessment

The European Food Safety Authority (EFSA) suggested the Margin of Exposure (MOE) be used to set priorities in risk management with respect to compounds that are both genotoxic and carcinogenic. The estimated daily intake for estragole is estimated from different food sources at 0.07 mg/kg bw/day; the MOE for pure estragole amounts to 129–471, and according to EFSA, a MOE lower than 10,000 can be considered a priority for human risk. The authors note that doses necessary to induce a genotoxic response are far from physiologically relevant human doses, and therefore the relevance of these adducts for tumor induction in humans in vivo needs to be further clarified.

Use During Breastfeeding

Basil appears to be safe during breastfeeding in the amounts found in foods, but many sources recommend that medicinal doses of basil not be used during lactation because of its estragole content and lack of safety information. Basil is a purported galactagogue but has also been used to decrease breastmilk oversupply in Persian traditional medicine; no scientifically valid clinical trials support either of these uses.

Other Substances of Concern

Thujones (0.001%–14.84%), safrole (0.1%), and coumarin (0.12%–0.37%) have been identified in essential oils and other preparations from leaves of O. basilicum. These substances each carry their own recognized toxicological profiles, and their presence at the higher ends of reported ranges may be of concern in concentrated preparations or essential oil applications.

General Tolerability

Doses of essential oil at levels examined in certain preclinical studies are deemed safe for oral administration. Due to polyphenolic and flavonoidic content, O. basilicum can be considered an important ingredient in healthy diets, and preparations may be effective as chemopreventive agents or adjunctive therapy in the treatment of different clinical conditions. Adverse event data from human studies remain limited due to the scarcity of clinical trials.

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