Mosquito 'invisibility cloak' discovered

Chemicals naturally found in humans could help produce better mosquito repellents

A naturally occurring substance found in human skin could yield a viable alternative to existing mosquito repellent, scientists say.

They say the chemical could help render people "invisible" to the insects.

At the American Chemical Society meeting, they revealed a group of compounds that could block mosquitoes' ability to smell potential targets.

When a hand with these chemicals was placed in a mosquito filled enclosure, it was completely ignored.

The team says their work could help prevent the spread of deadly diseases.

Mosquitoes are among the most deadly disease-carrying creatures. They spread malaria, which in 2010 killed an estimated 660,000, according to the World Health Organization (WHO).

Ulrich Bernier of the United States Department of Agriculture (USDA) who presented the work, said his team was exploring other options to Deet - a repellent which some do not favour.

Buzzing off

In fact, earlier this year a team of scientists said that the widely used repellent was losing effectiveness.

"Repellents have been the mainstay for preventing mosquito bites... [but] 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," said Dr Bernier.

A hand in a mosquito cage was not attractive when covered with the chemical

It has long been known that some people are more attractive to mosquitoes than others, but now the team has pinpointed a group of chemical components secreted naturally, that can mask human smell from the blood-sucking insects.

Dr Bernier explained that hundreds of compounds on the skin makes up a person's smell. In order to see what smells attracted mosquitoes, his team sprayed various substances onto one side of a cage.

It was the compounds that didn't attract any mosquitoes that they looked at further and when sprayed on a human hand, the insects did not react or attempt to bite.

'Invisible hand'

These chemical compounds, including 1-methylpiperazine, were found to completely block their sense of smell.

The compounds could be added into many cosmetics and lotions, Dr Bernier added.

"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 recognize that the hand is in there. We call that anosmia or hyposmia, the inability to sense smells or a reduced ability to sense smells."

Commenting on the work, James Logan of the London School of Hygiene and Tropical Medicine, said it was exciting to find out exactly which chemicals repelled mosquitoes.

"Although we already have good repellents on the market, there is still room for new active ingredients. The challenge that scientists face is improving upon the protection provided by existing repellents.

"If a new repellent can be developed which is more effective, longer lasting and affordable, it would be of great benefit to travellers and people living in disease endemic countries," Dr Logan told BBC News.

But he said that it would take many years before a new product would make it to market.