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The search for an effective repellent

July 1, 1993

The search for an effective repellent

By Robert A. Hedeen, Naturalist

Ever since prehistoric times, man has been searching for an effective insect repellent that will protect him from the bites of bloodsucking insects and their relatives. Indians resorted to the application to their bodies of rancid grease rendered from the fat of bears, raccoons, and opossums to protect them from bites, and since that time numerous chemical concoctions have been devised to accomplish a longer and more effective period of protection. Stale urine is frequently used by a few watermen on the eastern shore of Maryland to repel mosquitoes and other biting flies, and extracted oils of citronella, pennyroyal, clover, bergamot, and cedar have been touted as effective repellents as well as camphor, castor oil, creosote, crushed pepper, kerosene, juice of onions and leeks, and naphthalene. All of this suggests that previous attempts to find a good repellent have largely been unsuccessful.

When the U.S. entered World War II, there were four repellents for general use on the market, some with unpronounceable names: oil of cintronella as a general repellent for all creatures great and small; dimethyl phthalate for protection from the bites of malaria-carrying mosquitoes; ethylhexanediol (Rutgers 6-12) to repel mosquito vectors of yellow and dengue fevers; Indalone to prevent the bites of ticks and mites.

Realizing American troops would be deployed to all parts of the world where a variety of insect-borne diseases were prevalent, the Army Medical Service, in conjunction with the Agricultural Research Service of the U.S. Department of Agriculture, launched a program to develop an effective repellent for all types of dangerous insects and their relatives. This concern was quickly shown to be valid, as during the war more man-days were lost to duty from insect-borne diseases than from contact with enemy forces. For example, personnel of the 1st Marine Division suffered a 150 percent infection rate of malaria during fighting on Guadalcanal in the Solomon Islands in the southwest Pacific.

By 1942, the standard repellent issued to troops all over the world was a mixture of dimethyl phthalate, Rutgers 6-12, and indalone in a ratio of 6-2-2, which became the common name of this “bug juice.” This formulation proved to be a good general repellent, but it had several disadvantages. It was foul smelling and oily, caused severe irritation to the eyes and lips. It was a plasticizer in that it dissolved any plastic it contacted such as watch crystals and eyeglass frames. These disadvantages resulted in its relative ineffectiveness as many troops refused to use it.

During the period of the Korean War, a new standard repellent named M20-20 was developed and issued to troops. Dimethyl carbamate replaced dimethly phthalate in the 612, indalone combination, and, though the protection against bites was increased, the mixture still possessed the undesirable traits of its predecessor, resulting in its rejection by the average G.I.

In 1957, the Johnson Wax Company announced the discovery of the “magic bullet” in regard to insect repellents. The active ingredient of this new compound had the jaw-busting name of n, n, diethytoluamind, and was first marketed under the trade name “Off.” We know this product today as Deet, and over the years it has proven to be the most effective skin repellent ever developed. Most of the insect repellents sold today contain various concentrations of Deet in what is a $1 billion industry worldwide. About one-third of the U.S. population uses Deet each year.

The military was keenly interested in this new compound and subjected it to extensive testing. This writer was involved in some of the tests with certain species of mosquitoes and ticks that showed Deet was very effective against most biting flies, including mosquitoes, and ticks and mites, including chiggers. The formulation of Deet resembled an after-shave lotion and was only a mild plasticizer, and users readily accepted it. However, from the onset, there has been mild concern regarding the safety of Deet as it may be absorbed into the outermost layers of the skin. Over the years, a few rashes and skin irritations were noted after the material was used, and there were a smaller number of neurological disturbances attributed to Deet. A 1996 study of Persian Gulf War veterans concluded that Deet, combined with other chemicals soldiers used, might have contributed to the diverse group of physical disturbances that became known as Gulf War Syndrome. The overall safety and effectiveness of the casual use of Deet, however, has been well established over the past 45 years.

Science is never satisfied, and research into new and more effective repellents has continued. Again, Army researchers, working with the Agricultural Research Service, have recently announced they have found a compound that is far superior to Deet. This new repellent is identified only as compound SS220. The active ingredient in this new bug repellent is piperidine, which is found in trace amounts in black pepper. Chemists are now able to produce synthetic piperidine in the laboratory and formulate it into a clear liquid with a rather pleasing fruity smell. Extensive testing has shown SS220 to be just as effective a general repellent as Deet, if not better.

Toxicological tests on SS220 are being conducted at the Aberdeen Proving Ground in Maryland, and preliminary indications are that the material is completely safe. About half of the toxicity tests needed to win approval of the Environmental Protection Agency have been completed. It is predicted that SS220 will be given a more descriptive name and replace Deet as the repellent of choice for military and civilian use by the year 2006.

In the meantime, in the face of the pandemic of West Nile virus disease and the reappearance of malaria, dengue fever, and Lyme disease in this country, we should not hesitate to use our Deet when exposed to mosquitoes and other bloodsucking critters.

Dr. Robert Hedeen is a former resident of Maryland’s eastern shore and resided in the Chicago area from 1960-1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.

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