The mechanism mosquitoes use to zero in on their targets has been discovered by scientists in New York.
The malaria parasite is spread by mosquitoes
It is already known that the insects are very sensitive to carbon dioxide in exhaled breath.
Now a team led by Rockefeller University has found that they sense the gas using protein receptors in the structure extending from their jaws.
Writing in Nature, they say the discovery could aid the fight against insect-born diseases, such as malaria.
The Rockefeller team first examined fruit flies.
They discovered two protein receptors, Gr21a and Gr63a, which enable the fly to sense carbon dioxide with its antennae.
The researchers worked on fly nerve cells that did not normally respond to carbon dioxide.
They found that, if the Gr21a and Gr63a receptors were both switched on, the cells became excited by the gas.
They also showed that when Gr63a was mutated, the mutant flies no longer responded to the high levels of carbon dioxide that wild type flies avoid.
The researchers went on to examine malaria mosquitoes and found similar receptors in the insects' maxillary palp - a tiny finger-like structure extending from the jaws.
Lead researcher Professor Leslie Vosshall said: "Insects are especially sensitive to carbon dioxide, using it to track food sources and assess their surrounding environment.
"The neurons in insects that respond to carbon dioxide were already known, but the molecular mechanism by which these neurons sense this gas was a mystery.
"Though we don't know what other proteins might be involved in the signalling pathway, the identification of the carbon dioxide receptor provides a potential target for the design of inhibitors that would act as an insect repellent.
"These inhibitors would help fight global infectious disease by reducing the attraction of blood-feeding insects to humans."
Dr Simon Hay, an expert in malaria at the University of Oxford, said: "Curiously, the work could also open the opportunity for the development of attractants, used to lure mosquitoes away from humans.
"Increasing the distance mosquitoes have to fly for blood meals has long been known to increase their mortality and thus decrease disease transmission."