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Lactic Acid Repels Mosquitoes

What the Study Showed
How It Was Done
Why It's Important

What the Study Showed

In a 2001 study carried out at Japan's Toyama Medical and Pharmaceutical University, lactic acid was shown to be effective in repelling mosquitoes. In the results published in the Journal of Medical Entomology, researchers sought to clarify the mixed reports from earlier studies about whether lactic acid attracted or repelled these biting insects. It has long been hoped that this readily available compound found in sour milk may be able to supply an inexpensive and nontoxic alternative to presently available mosquito repellents, which often contain potent pesticides.

How It Was Done

The researchers examined the effects of lactic acid solutions both on human skin and, in a new variation on previous experiments, on the skin of hairless mice that don't sweat. The hand and forearm of human subjects were dipped into solutions of lactic acid diluted with distilled water, and then air-dried. The subjects then inserted both their arms into a test chamber containing 35 female mosquitoes of a type known to be avid biters (the mosquitoes' proboscises were amputated to avoid actual bites).

The number of mosquitoes that alighted on the hands and forearms were counted every 30 seconds for 10 minutes. Attraction or repellence was evaluated by comparing the number of times the mosquitoes landed on the treated arm to the number of times they landed on the control (untreated) arm. The experiment was repeated with various concentrations of lactic acid, and each concentration was repeated three to six times.

To determine whether there would be any difference between normal mosquitoes and those without the proboscis, and also to evaluate any difference between human skin and mouse skin, the experiment was repeated with normal mosquitoes, using anesthetized hairless mice. Treated and control mice were inserted into the test chamber containing 35 normal female mosquitoes, and the number of bites was counted for 10 minutes. Various concentrations of lactic acid were tested, and the results consistently showed that lactic acid does repel mosquitoes.

Why It's Important

In addition to the itch and irritation, a mosquito bite can spread potentially fatal diseases such as malaria. The search for a safe and inexpensive repellent has been intense. Research over the past 50 years has been contradictory as to whether lactic acid represents such an alternative, with some studies finding that mosquitoes are repelled by lactic acid, and others finding that they are actually attracted to it. The current study helps to clarify the apparent contradiction.

The Japanese researchers note that varying concentrations of lactic acid are already present in human skin and sweat. They also explain that the mosquito's physiology plays a part: A pair of nerve cells on the insect's sensory probe react in opposite ways to lactic acid, one spikes in frequency of impulses while the other decreases.

Source: Shirai Y, Kamimura K, Seki T, Morohashi M. L-lactic acid as a mosquito (Dipterai: Culicidae) repellent on human and mouse skin. J Med Entomol 2001;38(1):51-54.


Date Published: 06/30/2002
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