Leading with statistics on the incidence of West Nile virus and Lyme Disease infections, the Environmental Working Group (EWG) published a new guide on Monday to help consumers choose an appropriate, if not entirely non-toxic, bug repellent. Cautioning readers that "there's no sure, completely safe way to prevent bug bites," the authors quickly presented their top choice among the top four most-effective repellents, which are contained in many commercial products.

"DEET isn't a perfect choice nor the only choice. But weighed against the consequences of Lyme disease and West Nile virus, we believe it is a reasonable one," wrote the authors.

Along with the guide, which was the result of an 18-month fact finding mission, the authors produced a tip sheet that condenses their findings and recommendations down to a bare minimum of advisory notes. Generally, EWG recommends covering up with pants and long sleeves as a first line of defense against bugs, but for those who want or need a repellent, the organization provides four top choices. The following summarizes their findings.

The Big Four

Picaridin, a recommendation of the World Health Organization (WHO) for protection against mosquitoes that carry diseases, is not known to irritate skin and eyes, does not have a pungent odor, and does not dissolve plastics. It evaporates from the skin more slowly than DEET or IR3535 and may repel bugs for longer periods. Developed by Bayer AG in the 1980s and sold in the U.S. since 2005, picaridin "does not carry the same neurotoxicity concerns as DEET but has not been tested as much over the long term." Overall, EWG's assessment is that picaridin is a good DEET alternative with many of the same advantages and without the same disadvantages. EWG recommends picardin 5-10 percent for short protection times, and picardin 20 percent for longer periods.

IR3535, or 3-[N-Butyl-N- acetyl]-aminopropionic acid, ethyl ester, was developed by Merck & Co., Inc. in the mid-1970s and has been used in Europe for more than 20 years. Registered for use in the U.S. in 1999, IR3535 can be irritating to the eyes and may dissolve or damage plastics, but poses few other safety risks. Health authorities in Europe have not received reports of problems caused by this chemical. Consumer Reports determined that it performed as well as DEET against deer ticks and the Culex mosquitoes that sometimes carry West Nile virus, though the 20 percent formulation was slightly less effective than DEET in repelling mosquitoes that may carry yellow fever, dengue, and encephalitis. "In sum, IR3535 is a good DEET alternative with many of the same advantages and fewer disadvantages," the authors said. EWG recommends IR3535 20 percent for longer protection times.

DEET is the most common mosquito and tick repellent and "is a reasonable, if imperfect, choice," the authors write. Registered for public use since 1957, DEET gives off a distinct odor and may damage plastic, rubber and vinyl. On the plus side, when used as directed, DEET is considered safe by many public health authorities and organizations, including the Centers for Disease Control and Protection (CDC), the Environmental Protection Agency (EPA), the American Academy of Pediatrics, and WHO. That said, DEET is known to irritate the eyes and in intense doses may even induce neurological damage; though after reviewing reports of seizures, the EPA concluded the rate of adverse reactions to be very low -- about one per 100 million persons. Those who use DEET daily have reported suffering symptoms such as rashes, dizziness, difficulty concentrating and headaches. After reviewing the evidence, "EWG has concluded that DEET is generally safer than many people assume and remains a viable option for people in areas infested with disease-carrying pests...The EPA allows U.S. sales of repellents with up to 100 percent DEET, but increasing concentration does not increase efficacy.... We think it makes sense to follow Canadian government recommendations limiting DEET to 30 percent in any product and even weaker concentrations for young children." EWG recommends DEET 7-10 percent for short protection time and DEET 20-30 percent, especially when contained in time-release formulations, for longer periods.

Oil of lemon eucalyptus is the trade name for a repellent that originated as an extract of the eucalyptus tree native to Australia. If refined, paramenthane-3,8-diol, also known as PMD, results. Many products combine oil of lemon eucalyptus and PMD. Some testing has shown that concentrations of 20 to 26 percent PMD may perform as well as 15 to 20 percent DEET against both mosquitoes and ticks, though its maximum protection time against mosquitoes and ticks is shorter, according to the EPA. Oil of lemon eucalyptus/PMD is not recommended when the risk of West Nile virus is high or against sand flies or 'no-see-ums,' a particularly annoying biting insect. The CDC advises against the use of the oil on children under three years of age. EWG recommends PMD 10 percent for short protection time and oil of lemon eucalyptus 30-40 percent for longer periods.

Know Your Enemy

Carried by mosquitoes, West Nile virus infected more than 5,674 Americans last year (resulting in 286 deaths), according to the CDC. Meanwhile, the incidence of Lyme disease, which is spread by ticks, has more than doubled over the last 15 years, with 24,364 confirmed cases recorded in 2011. Both these illnesses, and other pest-borne diseases, can have serious and occasionally life-altering consequences.

A person is most likely to contract Lyme disease between late April and mid-July. Lyme disease infections typically occur in 13 Northeastern and Mid-Atlantic states, from Virginia to Maine, and the upper Midwest, mostly in Wisconsin and Minnesota. West Nile infections have been reported in almost every state, with the highest numbers in Texas, California, Illinois, Louisiana, Michigan, Mississippi, and Oklahoma. Peaking in August, West Nile virus infections occur primarily in the summer months.

"No single chemical completely repels important American ticks. Do not rely on any product to keep ticks away," reported the authors. "Perform tick checks at the end of the day or when returning indoors."

EWS suggests that consumers avoid products sold as combination sunscreen/repellents, as it is necessary to reapply these products more frequently than is safe to do so.

Who Is EWG?

The Environmental Working Group describes itself as "the nation's leading environmental health research and advocacy organization." Stating that the majority of its funding comes from private charitable foundations, the organization presents a partial list of its funders online. A substantial portion of its funds also comes from individuals. Serving as a watchdog, EWG advocates "to conserve land and water, produce and use energy responsibly and ensure that food and consumer products are free of harmful chemicals."

Source: Andrews D, Sharp R, Lunder S, Leibe N. Which is worse, bug bites or repellent? EWG's Guide to Better Bug Repellents. Environmental Working Group Publications. 2013.