Chemicals in human skin can make us 'invisible' to mosquitoes

Scientists have found that certain naturally-occurring substances on human skin can make us 'invisible' to mosquitoes by blocking the ability of the blood-sucking insects to smell and target their victims.

At the American Chemical Society's meeting in Indianapolis, researchers described a group of compounds that could block mosquitoes' ability to smell potential targets.

"Repellents have been the mainstay for preventing mosquito bites. The most widely used repellent, DEET, is quite effective and has been in use for a long time. However, some people don't like the feel or the smell of DEET," said researcher Ulrich Bernier of the United States Department of Agriculture (USDA).

"We are exploring a different approach, with substances that impair the mosquito's sense of smell. If a mosquito can't sense that dinner is ready, there will be no buzzing, no landing and no bite," Bernier said.

Female mosquitoes, which suck blood to obtain a protein needed to produce fertile eggs, can smell people from over 100 feet away.

The Mosquito and Fly Unit at the US Department of Agriculture's Agricultural Research Service-Center for Medical, Agricultural, and Veterinary Entomology in Gainesville, has been doing research on mosquito repellents since the 1940s.

They have accumulated information on substances secreted through the human skin or formed by bacteria on the skin that make some people more attractive to mosquitoes than others.

A person's scent, Bernier explained, comes from hundreds of compounds on the skin, many emitted through sweat and others produced by bacteria. To identify which of these attract mosquitoes, Bernier and colleagues used a special mosquito cage divided by a screen.

They sprayed various substances into one side of the cage, and documented the effects in attracting mosquitoes.

Some compounds, like lactic acid - a common component of human sweat - were definite mosquito lures, drawing 90 per cent of the mosquitoes to the screen. With other compounds, however, many of the mosquitoes didn't even take flight or seemed confused.

"If you put your hand in a cage of mosquitoes where we have released some of these inhibitors, almost all just sit on the back wall and don't even recognise that the hand is in there. We call that anosmia or hyposmia, the inability to sense smells or a reduced ability to sense smells," explained Bernier.

He said that a group of chemical compounds, including 1-methylpiperzine, block mosquitoes' sense of smell. This may help explain why mosquitoes fly toward some people but not others.