Lemon verbena (Aloysia citrodora) is a perennial shrub native to South America, cultivated globally for its intense citrus aroma. Its leaves emit a strong lemon scent, making it popular for herbal teas and flavoring agents. This analysis assesses the chemical composition of lemon verbena and the potential safety risks associated with inhaling the material when combusted, contrasting this with its traditional uses.
Primary Chemical Components
The high concentration of volatile compounds in the essential oil gives Aloysia citrodora its lemony fragrance. The primary component is citral, a mixture of two isomeric aldehydes: geranial and neral. Citral content often represents between 30% and 70% of the total essential oil composition, though this varies depending on the plant’s origin and growing conditions.
Other major monoterpenes present include limonene and 1,8-cineole (eucalyptol). Limonene is another citrus-scented compound, while 1,8-cineole contributes a sharp, camphor-like note. The leaves also contain smaller amounts of sesquiterpenes, flavonoids, and phenolic acids, which contribute to the plant’s overall biological activity.
The composition of these oils means that when the dried leaf material is burned, these highly concentrated chemical compounds are released into the smoke. This process of combustion, or pyrolysis, transforms the natural compounds into different, often harmful, byproducts.
Health Implications of Inhaling Combusted Plant Material
Inhaling the smoke from any burning plant material introduces particulate matter and various gases into the respiratory system, which can immediately cause irritation and inflammation. The specific risk with lemon verbena comes from the combustion of its concentrated essential oil components, particularly citral and limonene. Citral, a major component, decomposes when burned and produces irritating fumes.
Exposure to high concentrations of citral, even in vapor form, has been shown to cause severe respiratory tract irritation, including difficulty breathing and nasal discharge in animal studies. When heated, limonene thermally degrades, forming various oxidative products such as p-cymene and other compounds. Inhaling products of terpene combustion, even at low temperatures, can lead to the formation of secondary irritants and fine particles, which are known pulmonary irritants.
Combustion introduces the risk of inhaling thermal degradation products, which are distinct from the natural oils. There is no scientific evidence to support the safety or efficacy of smoking lemon verbena. The combustion process fundamentally changes the chemical profile to include known irritants and potentially toxic pyrolysis byproducts, posing an immediate risk of respiratory distress, especially for individuals with pre-existing lung conditions.
Standard Uses and Preparations
Lemon verbena’s traditional and safe applications utilize non-combustion methods to access its beneficial properties. The most common preparation is as an herbal infusion or tea, which is historically consumed to aid digestion and provide a calming effect. The heat from the water allows the volatile oils to be gently released for consumption without chemical alteration.
The leaves are also used extensively as a culinary flavoring, providing a fresh lemon note to dishes such as fish, poultry, soups, and desserts. Beyond internal consumption, the essential oil is incorporated into aromatherapy via diffusers or applied topically when diluted with a carrier oil. These methods avoid the high temperatures of combustion, allowing the natural compounds to be used in their intended form for their aromatic and therapeutic qualities.