Sweet basil

Sweet basil is an annual herb (occasionally a short-lived perennial in the tropics), 20–60 cm tall, with a thick square stem, much branching and fine hairs. The leaves are opposite, ovate to ovate-lanceolate, 3–11 cm long and 1–5 cm wide, with entire or slightly toothed margins, hairy and glandular-dotted with oil, hence glossy. Small white or pinkish flowers are borne in loose terminal spikes; the calyx has five teeth and the two-lipped corolla is about 4–6 mm long, with four stamens. The fruit is a small nutlet, the persistent calyx holding four tiny black seeds when ripe. The chromosome number is 2n = 48.

According to Kew POWO, the native range of sweet basil runs from tropical–subtropical Asia to northern Australia: India, Nepal, Bangladesh, the East Himalaya, Myanmar, Thailand, Laos, Cambodia, Vietnam, south-central and south-eastern China, Taiwan, the Philippines, Indonesia, New Guinea, Queensland and Western Australia. It favours seasonally dry ground, growing in wasteland, roadsides and cultivated land. From there it was domesticated thousands of years ago (cultivated in Egypt some 3,000 years ago) and spread through the tropics and warm temperate zones of Europe, Africa and the Americas, naturalising in many places. In Vietnam it is common in home gardens and market plots from the plains to the lower hills.

The aroma and activity of sweet basil come chiefly from essential oil stored in glands on the leaves, flowers and stems (about 0.2 g per 100 g fresh weight, higher in oil-rich cultivars). Composition varies strongly with chemotype, genotype, climate and season: the main groups are linalool (European sweet basil, up to about 68%), methyl chavicol/estragole (Asian basil, up to about 86%), methyl eugenol and methyl cinnamate. There are also eugenol (lemon basil), 1,8-cineole, camphor, geraniol, citral, nerol, α- and β-pinene, β-caryophyllene, germacrene-D, together with rosmarinic acid, quercetin, rutin, apigenin and other flavonoids, tannins and saponins. This compound profile produces the plant's characteristic anise–clove aroma.

Notable studies include a double-blind randomised controlled trial (2021, Philippines) in 24 patients with stage 1–2 hypertension: 128 mg of dried leaves a day for two weeks added to standard medication significantly lowered blood pressure (p < 0.0001) versus controls. A single-blind placebo-controlled randomised trial (2025) in patients with major depressive disorder, using a hydroalcoholic leaf extract alongside sertraline, showed improved HAM-A anxiety and BDI depression scores after four weeks. Essential oil of Western Ghats basil (India, 2014), rich in methyl eugenol (39.3%) and methyl chavicol (38.3%), was bactericidal and fungicidal; a study in Molecules (2023, Morocco) reported inhibition of α-amylase (IC50 50.51 µg/mL), α-glucosidase (IC50 39.84 µg/mL), lipoxygenase (IC50 18.28 µg/mL) and tyrosinase (IC50 68.58 µg/mL). A 2020 review adds antioxidant, anti-inflammatory and antidiabetic effects.

On safety, sweet basil is regarded as harmless at food doses; acute and chronic animal toxicity studies (Molecules 2023) showed good tolerance. Note should be taken that estragole and methyl eugenol — constituents of many Asian chemotypes — caused liver tumours in rodents at high doses; methyl eugenol has been classed as Group 2B (possibly carcinogenic to humans), so concentrated essential oil should not be overused, especially by young children, pregnant women and people with liver disease. Undiluted essential oil should not be taken orally without guidance. The species is a worldwide crop and is not threatened at species level; supply comes mainly from cultivation. Conservation largely means keeping chemotype and landrace diversity in gene banks, since valuable chemotypes can be lost when only a few commercial cultivars are grown.