Choosing an insect repellant

by Janet L. Andersen, PhD*


In Vermont, mosquitoes carry West Nile virus and eastern equine encephalitis virus, and ticks carry Lyme disease, anaplasmosis, and babesiosis. There is no absolute protection against being bitten by an infected mosquito or tick, but there are precautions when taken together that substantially reduce your risk.



Health Vermont and other trusted authorities recommend wearing long-sleeve shirts, tucking long pant legs into boots, and conducting a thorough body examination after going back indoors. Insect repellents can further reduce risk, but no synthetic or natural chemical repels 100% of mosquitoes or ticks all of the time. A single bite can transmit disease.


The United States Environmental Protection Agency (EPA) requires proof that registered products repel pests named on the label, but allows some natural chemicals considered to be safe to be sold without registration and without proof they repel insects. This loophole allows products to be sold that may or may not work or that may work for such a short time as to be functionally ineffective. Examples of ingredients used in unregistered repellents are:  cedar oil, eugenol, geranium oil, peppermint oil, lemongrass oil, rosemary oil and soybean oil.


Insect repellants registered by the EPA as scientifically proven to be effective have these active ingredients:


  • N,N-Diethyl-meta-toluamide (DEET)
  • Picaridin
  • Amino acid IR3535 derived from β-alanine
  • Citronella oil derived from dried cultivated grasses
  • Oil of Lemon Eucalyptus extracted from leaves
  • 2-undecanone or methyl nonyl ketone
  • Catnip (or catmint) oil extracted from leaves.


Registered products have “EPA Reg. No.” with the individual products number usually on the back side of the container.


Read the entire label, including the fine print, as if your health and safety depended on it!  Not all of these compounds repel ticks. Most products that repel mosquitoes also repel black flies. DEET, citronella, and catnip oil products include a warning to use soap and water to wash skin and sometimes clothing after use. Most repellents may cause skin irritation and should not be applied to cuts, sunburned or otherwise damaged skin, such as after shaving. Generally, a product states how long it is effective for ticks, mosquitoes, and black flies and how many times each day a product can safely be applied.


These warnings also apply to products used to treat your lawn for mosquitoes and ticks.  Only EPA registered products have been reviewed for safety and efficacy. Scrumptiously follow the label, including time between application and when you or your pets can reenter the treated area and other instructions for keeping the chemical off pets and humans.


*Dr. Andersen retired to Barnard from the EPA where she managed natural pesticides. She has a PhD in Plant Pathology from University of Maine and a Master of Science from the University of California, Berkeley.


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