Lemongrass

Lemongrass (Cymbopogon citratus) is a perennial grass forming dense tufts, usually 1–1.5 m tall and occasionally reaching 2 m, with a short rhizome and a vigorous, deep fibrous root system. Leaves are clustered in bundles, narrow-linear, 30–90 cm long and 5–15 mm wide, with long-tapering tips, smooth surfaces, slightly scabrous margins and a prominent midrib; the sheaths are smooth and often red-purple towards the base. The ligule is a thin, membranous 1–2 mm flap. The inflorescence is a 30–60 cm panicle of paired spikelets, but under cultivation the plant flowers very rarely and sets almost no seed — which is why lemongrass is propagated vegetatively by splitting tufts and planting stem cuttings rather than from seed.

According to Kew's Plants of the World Online the native range of Cymbopogon citratus is South Asia — specifically southern India and Sri Lanka — in the wet tropical biome; from there it has been introduced and become common across the tropics and subtropics. Today the main production areas include India, China, Sri Lanka, Vietnam and Guatemala, together with many countries in Southeast Asia, Africa and South America. In Vietnam, lemongrass grows and is cultivated on plains, riverbanks and footslopes from north to south, usually on loose, adequately moist soil; the plant favours full sun, and leaf biomass peaks under year-round hot, humid conditions.

Fresh leaves are steam-distilled into lemongrass oil at a yield of roughly 0.3–0.5% of fresh leaf weight, in which citral — the mixture of two citrus-scented isomers, geranial (citral A) and neral (citral B), usually in a ratio of about 1.2–2:1 — accounts for 65–85%. Besides citral the oil contains myrcene (about 5–20%), geraniol, limonene, β-caryophyllene, nerol, citronellal, 1,8-cineole and geranyl acetate. It is the monoterpene-aldehyde framework of citral that determines the characteristic fresh-citrus note and most of the oil's biological activity; leaf citral content peaks just before the plant switches to flowering, so harvest timing directly affects oil quality.

Lemongrass oil has been studied extensively for oral health: the scoping review by Kusuma et al. (Pharmaceuticals, 2024) collates clinical trials using lemongrass essential oil or lemongrass-containing mouthwash for gingivitis, periodontitis and dental caries, in some of which it matched or slightly outperformed chlorhexidine. Gao et al. (Frontiers in Cellular and Infection Microbiology, 2020) showed that lemongrass oil and citral inhibit dual-species biofilms of Staphylococcus aureus and Candida, pointing to potential in bacterial–fungal infection control. Boukhatem et al. (Libyan Journal of Medicine, 2014) reported strong anti-inflammatory and antifungal activity in vivo in a rat paw-oedema model. Shah et al. (Journal of Advanced Pharmaceutical Technology & Research, 2011) and Tibenda et al. (Frontiers in Pharmacology, 2022) review the pharmacology of the species and of the genus Cymbopogon, covering antibacterial, antioxidant, hypoglycaemic and anti-inflammatory effects in preclinical work.

On safety, citral is a well-known skin sensitiser (hapten) that can irritate skin and mucous membranes when undiluted oil is used, so it should always be diluted and kept away from the eyes; Rosol et al. (Food and Chemical Toxicology, 2023) confirm that lemongrass oil has been assessed FEMA GRAS as a food flavouring, though only for flavouring-level use. Lemongrass is quite distinct from Java citronella (C. winterianus) and Sri Lankan citronella (C. nardus) — the citronellal-rich species used as mosquito repellents — and the three must not be confused when used medicinally. For conservation, the species is Not Evaluated by the IUCN and is not listed in CITES; C. citratus is almost sterile and widely cultivated, so wild populations face little pressure, but genetic diversity is maintained mainly through clonal lines, making conservation of local landraces and tissue banks a priority.