Lemon balm (Melissa officinalis) is a fragrant, perennial herb in the mint family, known for its pleasant, citrusy aroma and traditional uses in teas and cooking. Its leaves contain aromatic compounds that give it a sharp, lemon scent. The claim that lemon balm can naturally repel insects, particularly mosquitoes, has made it popular among gardeners. This article explores the science behind this assertion, examining the herb’s active components and its practical effectiveness as a natural bug deterrent.
Citronellal: The Key Repellent Component
The repellent action of lemon balm is primarily attributed to volatile organic compounds concentrated in the plant’s leaves and stems. The most significant compound is citronellal, a monoterpenoid aldehyde responsible for the herb’s characteristic lemon scent. Some northern European varieties can contain high concentrations of citronellal, sometimes approaching 38% of the essential oil composition.
Citronellal is a well-known insect repellent, similar to the compound found in citronella oil, working by interfering with an insect’s sensory organs. Mosquitoes and gnats locate hosts by sensing cues like carbon dioxide and body odors. The strong scent of citronellal effectively masks these attractants. Other related terpenes, such as geranial and neral, also contribute to the repellent effect by acting as sensory irritants.
Scientific Evidence of Efficacy
Research suggests that lemon balm does possess repellent properties, particularly against common pests like mosquitoes and the Aedes aegypti species, which transmits diseases like Dengue fever. The essential oil extracted from the leaves has demonstrated both larvicidal and insecticidal activity in laboratory settings, validating the traditional use of the plant.
However, the efficacy of lemon balm depends highly on the concentration of active compounds and the application method. While concentrated essential oil shows significant results, raw plant material or simple homemade preparations offer limited protection. For instance, a basic topical spray made from steeped leaves may only be effective for one to two hours before reapplication is necessary, as the volatile oils quickly evaporate.
This short-term effectiveness contrasts with highly concentrated synthetic repellents like DEET (N, N-diethyl-meta-toluamide). DEET is the most widely used synthetic repellent and is known for providing protection that can last for several hours. Although lemon balm is suggested as a natural alternative, its strength and longevity are generally lower than commercial products.
Methods for Using Lemon Balm as a Repellent
The most direct way to use lemon balm as a personal repellent is to crush the fresh leaves and rub them directly onto exposed skin. This action releases the concentrated oils, providing a quick, though temporary, barrier against mosquitoes and gnats. Because the volatile compounds evaporate rapidly, this method requires frequent reapplication, especially in areas with a heavy insect presence.
Another common strategy involves planting the herb near outdoor living spaces, such as patios, decks, or windows. Growing lemon balm in containers or garden beds near entry points acts as a localized perimeter deterrent. Although the growing plant does not create a strong enough concentration to completely clear an area of bugs, the presence of the fragrant leaves helps discourage pests from settling nearby.
For a slightly more lasting topical solution, a simple DIY spray can be made by steeping a large handful of fresh leaves in a base like witch hazel or alcohol for one to two weeks. The witch hazel extracts the water-soluble and some oil-soluble components, creating a basic spray that can be applied to the skin. It is important to remember that even these infused sprays will require reapplication every few hours to maintain their repellent effect.