In traditional practice as a personal protection measure against host-seeking mosquitoes, plant-based repellents have been used for generations. A valuable resource for the development of new natural products, the knowledge gained with repellent plants through ethnobotanical studies is a very valuable resource. Though sometimes a misconception, commercial repellent products containing plant-based ingredients, are commonly perceived as “safe” in comparison to long-established synthetic repellents and are becoming increasingly popular as a result. To date, insufficient studies have followed for repellent testing based on the standard WHO Pesticide Evaluation Scheme guidelines. Snell Scientifics would like to discuss essential oils as natural repellents.
Essential Oils that Repel Mosquitoes, Insects & Ticks
Lemon eucalyptus, or Corymbia citriodora (Myrtaceae), extracted from the leaves of lemon eucalyptus trees, is a rather potent natural repellent discovered in the 1960s from Chinese traditional medicine where plants were used and as screening occurred. Comprising 85% citronella, lemon eucalyptus essential oil was used for the fresh smell, primarily in the cosmetic industry. Although it was discovered being far more effective at repelling mosquitoes than the essential oil itself, is the waste distillate left after hydro-distillation of the essential oil. With the effect lasting from several minutes to several hours, many plant extracts and oils repel mosquitoes. Although they are only effective repellents as a short-term remedy because they rapidly evaporate leaving the user unprotected. The active ingredients tend to be highly volatile.
Citronella. The citronella genus essential oils and extracts are frequently utilized ingredients of plant-based mosquito repellents. Rather than for its efficacy, citronella has found its way into many commercial products through its familiarity. Deriving from the French citronelle around 1858, citronella was originally extracted for use in perfumery. At the beginning of the 20th century, the Indian Army used it to repel mosquitoes and it was then registered in 1948 for commercial use in the USA. Used at concentrations of 5-10%, modernly speaking on the market, citronella is one of the most widely used natural repellents. Higher concentrations can cause skin sensitivity though this is lower than most other commercial repellents. There are relatively few studies, however, that have been performed to determine the efficacy of citronella essential oils as arthropod repellents. Although formulation of the repellent is very important, citronella-based repellents only protect from host-seeking mosquitoes for about two hours.
Neem. As a natural alternative to DEET, neem is widely advertised, and has been tested for repellency against a range of arthropods of medical importance. Contrasting with findings of intermediate repellency by other researchers, a handful of field studies from India have shown very high efficacy of Neem-based preparations. The solvents used to carry the repellents, however, have contrasting results that may be due to differing methodologies. Neem for use as a topical insect repellent has not been approved by the EPA and has a low dermal toxicity but can cause skin irritation.
Natural oils and emulsions. Quite a few oils have shown repellency against mosquitoes. They work by reducing short range attractive cues, reducing the evaporation and absorption of repellent actives, and contain fatty acids known to repel mosquitoes. A commercial preparation containing glycerin, lecithin, vanillin, oils of coconut, geranium, and 2% soybean oil can achieve similar repellency to DEET, as a bite blocker, and provide just over 7 hours of mean protection time. Soybean oil helps contribute to repellency but is not evaluated as a repellent on its own.
Essential oils. Frequently used as insect repellents throughout the globe, are essential oils distilled from members of the Lamiaceae (mint family), Poaceae (aromatic grasses) and Pinaceae (pine and cedar family). For food flavoring or in the perfume industry, almost all of the plants used as repellents are believed to be a safer, natural alternative to DEET despite many oils causing contact dermatitis. Pine oil, pennyroyal, peppermint, lemongrass, geraniol, cedar oil, thyme oil and patchouli are all plant essential oils in many commercial repellents. The most effective of these are peppermint oil, cedar oil, thyme oil, geraniol, patchouli and clove and have been found to repel malaria, filarial and yellow fever vectors for a period of 60-180 mins.
Essential Oil Toxicity Screening
To rapidly evaluate the performance of new sources of ingredients for your production products, Snell Scientifics works with our clients to develop a tox screen platform. When applied in the field, the success of your product can be confirmed in terms of the repellency and toxicity properties of the essential oils used. To ensure that your product performs to the standards you set, we can help you cost effectively, no matter the pest specie(s) you are targeting. Contact us to learn more today.
