Research & Education

Botanicals to Ward Off the Bugs


Most of the nation was surprised by an unseasonably warm winter. Many enjoyed the extra days of warmth but the downside is the heightened allergy and insect burden that followed. Outdoor enthusiasts have found they need to take extra precautions against vectors during their summer activities. Mosquitoes ticks and other vectors carry dangerous diseases that are quickly escalating at rates the CDC is not yet willing to report. These include Lyme disease Rocky Mountain spotted fever and West Nile virus.

In lieu of these threats we cannot afford to ignore the pleas to adequately protect ourselves; however with the plethora of toxic chemical repellents on the market the question arises ‘Are there safer options?’ 

Dangers of Chemical Repellents

The toxicity of chemical insect repellents causes apprehension in many who are already burdened with toxins and health challenges. DEET the king of all insect repellents is perhaps the most toxic being labeled as an acetylcholinesterase inhibitor and causing neurotoxicity in both insect and mammals. Further when used with other chemical repellents and sunscreens absorption and toxicity is heightened. DEET has also been shown to be capable of blocking sodium and potassium currents at low doses similar to the effect of lidocaine and other topical anesthetics explaining why it often has a numbing effect on human skin. DEET has already been widely associated with skin and mucus membrane irritation cardiovascular and neurological symptoms and is labeled as being especially dangerous for children and pregnant women in their first trimester.

So what are some alternatives?

Oil of Lemon Eucalyptus

Oil of lemon eucalyptus is the first botanical insect repellent approved by the Environmental Protection Agency (EPA) for offering protection that rivals that of DEET against mosquitoes and ticks. The greatest concern with plant-based repellents has been the issues of limited duration and effectiveness. While most may show effectiveness for up to 75 minutes a traditional chemical repellent with a 30 to 34 percent concentration of DEET is effective for up to 12 hours. Oil of lemon eucalyptus has shown effectiveness up to 7 hours at a concentration of 30 percent. 

Citronella Grass

Citronella is among the most common botanical insect repellents used in non-contact venues such as candles torches lawn and environmental sprays. However studies have shown citronella grass (Cymbopogon nardus) to be a powerful repellent against deer tick nymphs offering 35 hours of protection at high concentrations. This research is exciting since the nymph stage of ticks is the most dangerous for contracting Lyme disease due to the fact that the nymphs are so small they are often overlooked when they attach to their victims. For this reason alone citronella should be a welcome addition to plant-based insect repellents. 

Oil of Neem

Neem oil has often been used in veterinary medicine as an insecticide for farm animals and studies in India show very high efficacy of neem-based preparations as an insecticide for agricultural applications. Neem cake a byproduct of neem oil extraction has more recently been recognized as a source of mosquitocidal metabolites that are effective against mosquito ova larva and pupa. According to the journal Crop Science and Horticulture “Neem oil contains at least 100 biologically active compounds. Among them the major constituents are triterpenes known as limonoids the most important being azadirachtin…which appears to cause 90% of the effect on most pests.” 

Other Botanicals

Many other botanicals have shown insecticide properties and promising protection against vectors. Lemongrass and Mexican marigold were studied at various doses and found to be highly effective against sandflies at very low doses. In another study very low doses (1-5%) of citronella hairy basil and vetiver resulted in an insect escape rate of 73-89 percent indicating good repellent activity. Over the years many other essential oils including geranium clove peppermint lavender cedarwood melaleuca and thyme have shown various degrees of insect repelling activity and are readily found in combination products. 

The success of botanicals in repelling insects has not been questioned as much as the duration of efficacy which becomes an important factor in rating insecticides and approving them for the general public. Studies of combined botanicals prove to be more effective than single botanicals while preparations that include potentiators such as vanillin and soybean oil can increase protection time significantly. Of course a simple solution would be to apply plant-based insect repellent frequently rather than avoid repellents altogether.

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For more information related to this topic please listen to the following Nutrient Roundtable discussion: