CO2 in exhaled air is the sensory cue for female blood-sucking mosquitoes, this causes host-seeking flight and navigation towards the target. Mosquitoes can also detect minute changes in the concentration of the gas and track it back to humans breath. Link At last I know why I attract so many mosquitoes Scientists at the University of California, Riverside, tested smelly chemicals on three species of mosquito: Anopheles gambiae, which spreads malaria; Culex quinquefasciatus, which spreads filariasis and West Nile virus; and Aedes aegypti which spreads dengue and yellow fever. Between them these insects are thought to spread disease to half a billion people each year and cause millions of deaths. The researchers identified three groups of chemicals, which disrupt a mosquito's carbon dioxide receptors.