Melissa officinalis, commonly known as lemon balm, is a perennial herb belonging to the mint family, Lamiaceae, and is native to Eurasia. This plant is easily recognized by its strong, uplifting lemon scent. For centuries, lemon balm has been cultivated for its culinary, traditional medicinal uses, and its distinct aromatic properties, which are often employed for mild pest deterrence. The plant’s effectiveness as a natural repellent stems entirely from the volatile oils contained within its foliage. This article explores which pests lemon balm helps to discourage and the underlying mechanism responsible for this action.
Specific Pests Deterred by Lemon Balm
Lemon balm is most widely cited as a deterrent against various biting insects that commonly plague outdoor activities. Its primary target is the mosquito, with evidence suggesting that its essential oil can be effective against species like Aedes aegypti. The strong citrus aroma acts to confuse and deter these pests, preventing them from locating a potential host.
This repelling action also extends to other small flying insects, including gnats and some species of biting flies. Gardeners also note an effect on certain garden pests. The presence of the plant may help to discourage soft-bodied insects like aphids and some caterpillar varieties, such as cabbage worms, from nearby vegetable crops.
Anecdotal reports suggest that lemon balm can also deter ants when planted strategically or when its crushed leaves are used as a barrier. The herb functions as a deterrent, not a lethal insecticide, and its effectiveness is strongest against insects that rely heavily on scent to navigate. For the plant to actively repel these pests, its aromatic compounds must be released into the immediate environment.
Chemical Compounds Responsible for Repellency
The insect-repelling power of lemon balm is concentrated in its volatile organic compounds (VOCs), which are responsible for the plant’s characteristic lemon fragrance. The most significant of these compounds is Citronellal, a monoterpenoid aldehyde that can make up a substantial portion of the plant’s essential oil. Citronellal is a well-known natural repellent that mimics the action of citronella oil.
This compound, along with others like Citral, Geraniol, and Citronellol, acts by overloading the insect’s olfactory system. Mosquitoes rely on detecting carbon dioxide, body heat, and specific odor cues to locate humans and animals. The intense, pungent aroma of the lemon balm oils effectively masks these host-seeking signals, making it difficult for the pests to find their targets.
The combination of these volatile chemicals creates an aromatic barrier that insects find highly unpleasant and disorienting. Therefore, the mechanism is one of sensory disruption rather than a toxic effect.
Methods for Using Lemon Balm as a Repellent
The most direct method for immediate, short-term protection is the topical application of fresh leaves. Crush a handful of lemon balm leaves to rupture the oil glands and release the concentrated volatile compounds. The bruised leaves or the resulting green liquid can then be rubbed directly onto exposed skin areas like the arms, legs, and neck.
A second practical method involves strategic planting of the living herb in areas where people congregate outdoors. Placing potted lemon balm plants near patios, decks, or doorways helps to release a mild, deterrent scent into the air. However, the plant itself offers minimal protection unless the foliage is physically rustled or brushed against, which helps the repelling oils escape into the surrounding atmosphere.
A more concentrated application involves creating homemade sprays or infused oils, typically using a high-proof alcohol or carrier oil to extract the essential compounds. Infusing the leaves in witch hazel or oil for several weeks can produce a liquid that can be strained and applied to the skin or clothing. For maximum potency, concentrated lemon balm essential oil should be added, as the concentration of the active compounds is significantly higher than in simple infusions.
Safety and Efficacy Considerations
While lemon balm is generally considered safe for topical use, particularly in its fresh leaf form, it is always prudent to perform a patch test on a small area of skin before widespread application. This precaution is especially important when using concentrated homemade sprays or essential oils, as high concentrations of Citronellal can cause skin sensitivity or irritation in some individuals.
Homemade or crushed-leaf preparations are typically less potent and shorter-acting than commercially available synthetic alternatives, such as those containing DEET. The protective effect of topical lemon balm preparations often lasts for two hours or less, necessitating frequent reapplication for continuous coverage.
For repellant purposes, internal consumption of lemon balm, such as drinking the tea, is not a reliable or recommended method of pest control. The herb’s compounds are most effective when applied directly to the skin or released into the immediate air space. When using essential oils, it is also important to ensure they are properly diluted in a carrier, as applying undiluted essential oils can cause adverse skin reactions.