Insect repellents were researched and reviewed by Consumers Union and the results published in the July, 1993, issue of Consumer Reports magazine. Twenty-one different commercial products were tested, including aerosol and pump sprays, squeeze bottles or tubes, and wipe-on sticks and towelettes. Repellents were tested against two species of mosquitoes and against stable flies. Only mosquito repellency is summarized here.
A measured amount of each repellent was applied to the forearms of research volunteers. After the repellent had dried, the volunteers 'thrust their arms into a cage of 500 hungry mosquitoes' and waited five minutes to see if mosquitoes would bite. The test for each repellent was repeated every hour until the repellent stopped working or till 7 1/2 hours had passed.
Most of the products tested contained DEET, the active ingredient found in most insect repellents. DEET is the common, abbreviated name for N,N-diethyl-meta-toluamide, a repellent developed approximately 40 years ago and still the most effective repellent available. As has been shown in the past, the amount of DEET in a repellent product determines how long an application of repellent will be effective. In the Consumer Reports ranking, the product that lasted the longest, and was rated 'Excellent' was a 40% DEET aerosol that 'warded off mosquitoes for more than six hours.' Nearly as good, with a rating of 'Very Good' were several products of 20 to 40% DEET that protected for four hours.
As we have said in the past, there is little reason to use products with a very high concentration of DEET active ingredient. The Consumer Reports research indicates moderate concentration products with 20 to 40% DEET are 'only a notch weaker' in their repellency against mosquitoes. Further, sparing use of lower concentration materials reduces unnecessary or excessive exposure and the chances of reported, but very rare, neurological problems. Other Consumer Reports suggestions to reduce exposure are: Don't apply repellent near eyes, on lips, or on broken skin; To apply a spray to your face, spray your palm and then spread the repellent carefully; Avoid breathing spray; Don't use near food; Wash repellent off with soap and water when it's no longer needed.
Repellents that do not contain DEET were also included in the research trials. 'Natural' repellents such as citronella and a mixture of citronella, cajuput grass, sassafras, peppermint and myrrh were tested. Avons Skin-So-Soft bath oil was also in the trial because of the large number of testimonials reporting its effectiveness.
Products that did not contain DEET did not do well in this research. The 'natural' repellents 'couldn't ward off aggressive mosquitoes for even half an hour' and Skin-So-Soft 'was equally ineffective.' All non-DEET products were rated 'Poor' in repellent efficacy against mosquitoes.
Reference: Consumer Reports, Volume 58, No. 7, July, 1993, pages 451 - 454. Published by Consumers Union of U.S., Inc., 101 Truman Avenue, Yonkers, NY 10703-1057.
This article originally appeared in the June 30, 1993 issue, pp. 1993 issue, pp. 107-108.