New Study Questions Long-Lasting Effects Of Mosquito Repellent

PITTSBURGH (KDKA) -- A new study suggests that DEET, a mosquito repellent, may not be effective in the long run, but a local expert argues otherwise.

Just looking at a dead mosquito magnified can send shivers down your spine, and they've been blamed for spreading malaria, yellow fever, dengue fever, encephalitis and West Nile virus.

Bill Todaro, the medical entomologist at Allegheny County Health Department, adds that a chikungunya virus is now coming into the U.S. from the Caribbean Islands.

Not to mention, they can flat out ruin a day on the water, a walk in the park or a backyard picnic. Some may take it as a cost of summer, but most people head for the brightly colored cans containing DEET.

"DEET is a product that confuses the mosquito's sensory system," Todaro said. "They are smelling carbon dioxide and everything that comes out of your skin, they are focused on you, and when they get down close to the skin to bite, they get this mixed signal from the DEET that something's not right here, and they don't land."

But a study out of the London School of Hygiene and Tropical Medicine says mosquitoes may be deterred at first, but later ignore the DEET and will bite you anyway.

Todaro has his doubts about the London findings about mosquitoes, saying that they are still repelled by those products.

"Well, they can learn to adapt to new sensors," he said. "Insects have a tiny little brain, but it works pretty well. But I don't believe that DEET is no longer a successful repellent. DEET is still a very good repellent for most cases."

Todaro says in a lab environment, mosquitoes might indeed learn to ignore DEET but "for the general 'Joe Schmo' mosquito that's coming out of an old tire or something, they are still going to be repelled by DEET."

Whatever you use, Todaro says it should last six to eight hours, and when applying it, aim low first.

"Mosquitoes will bite your feet, if you have sandals or bare feet or whatever. Most mosquitoes like people's feet a lot," he said.

Of course, any exposed skin is vulnerable. As for Citronella, an oil extracted from a perennial grass, Todaro says it has, "some repellent properties. It does produce an aroma, a lemony aroma, that is slightly repellent to mosquitoes."

But a study out of North Dakota State University suggests in an open environment, like a picnic or in your backyard, burning citronella is a waste of time, and Todaro agrees.

"Any repellent aroma that would come out of this would be wafted away by any moving air," he said.

An enclosed porch, maybe, but Todaro says a better bet is to use some of the yard pre-treatments or fogs.

"You spray it into the vegetation, and it will contact that mosquitoes, and they will drop down, but it has no residual. Nothing to keep it there to keep the mosquitoes from coming back."

Todaro also says to remember that mosquitoes can and will bite through your clothes.

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