Lemon balm

Lemon balm is a bushy perennial 30 to 80 centimetres tall, with square stems, crinkled heart-shaped leaves that smell of lemon when rubbed, and small white or pale yellow flowers that attract bees. The fruits split into four tiny nutlets, each about 1.5 millimetres, dark brown to black, smooth and oval, so small that a gram holds about a thousand seeds. They have little flavour themselves. Seeds are sold for raising plants, and the leaves are sold fresh and dried for tea. The seeds need light to germinate, so they should be pressed into the surface of soil and not buried deeply. The plant spreads freely by self-seeding.

Lemon balm is native to southern Europe, the Mediterranean basin, North Africa and western Asia, and it has become naturalised in much of Europe and North America. The genus name Melissa is the Greek word for honeybee, a reference to the plant's attraction for bees, and beekeepers have long rubbed hives with it. The common name balm is a short form of balsam, a reference to the plant's soothing fragrance, and lemon refers to its scent. The species name officinalis means it was a plant of the apothecary's shop.

Greek and Roman writers such as Theophrastus, Dioscorides and Pliny described lemon balm as a plant for bees and as a medicine for stings, digestion and wounds. Arab physicians including Avicenna wrote about its ability to lift the spirits and settle the stomach, and it was carried by Arabs to Spain. In medieval Europe, monasteries grew balm, and Charlemagne reportedly ordered it grown in imperial gardens.

In 1611, Carmelite monks in Paris began making a distilled tonic called Eau de Mélisse des Carmes, flavoured with lemon balm, angelica root, nutmeg and coriander, which was sold as a remedy for headaches and nervous complaints and remained popular for centuries. Paracelsus and later herbalists praised the plant, and John Evelyn wrote that balm is sovereign for the brain.

In the late twentieth century, researchers examined lemon balm extracts in small clinical trials for stress, sleep and cold sores, leading to its use in cosmetics and herbal supplements in Europe. German authorities have approved its use in leaf form for nervous sleep disorders and digestive discomfort. The plant also became a favourite of beekeepers and garden designers for its fragrance and generous growth.

The seeds are sown in spring to grow plants, though they are also sometimes sprinkled into herbal blends in tiny amounts. Leaves are made into teas, added to salads, fruit dishes, fish, poultry, sauces, ice cream and lemonade, and used to flavour liqueurs and vinegars. Dried leaves lose much of their aroma, so fresh use is preferred. Extracts feature in sleep and relaxation products, and a topical cream is sold for cold sores. The plant is also grown for bees and for the essential oil, called melissa oil, which is expensive and used in perfumery and aromatherapy.

Small clinical studies suggest lemon balm leaf extracts may modestly reduce anxiety and improve sleep quality or mood, particularly when combined with valerian, and topical creams may shorten cold sore healing time. The effects are typically mild, and trials are small and varied, so confidence is limited. The active compounds include rosmarinic acid and volatile oils such as citronellal and geranial. Seeds are not an established source of these compounds, and tea of leaves is the usual traditional form.