Short answer
A mosquito does not lock onto you all at once. It follows a chain of cues, and each one takes over as the insect gets closer. From a distance, it tracks the carbon dioxide you exhale. As it flies in, it uses vision to steer toward dark, high-contrast shapes. Up close, it reads your body heat, the moisture around your skin, and the specific chemistry of your skin odor. The last few inches are settled by heat and scent together. No single cue tells the whole story, and the cues reinforce one another, which is part of why mosquitoes are so hard to shake (Sources 1, 2).
Carbon dioxide: the long-range signal
Every time you breathe out, you release a plume of carbon dioxide. Mosquitoes are tuned to detect it, and it is the cue that works at the greatest distance. In wind-tunnel and field-style experiments, a CO2 plume drew mosquitoes from roughly 10 to 50 meters away and switched on their host-seeking behavior (Source 2).
Carbon dioxide does more than pull a mosquito in a direction. It acts as a gate that primes the other senses. In one study, mosquitoes engineered to lack a working CO2 receptor (the Gr3 gene) also lost their normal responses to heat and to lactic acid, a compound found on human skin. In plain terms, a whiff of CO2 tells the mosquito that a warm-blooded animal is nearby and makes it pay attention to heat and scent it would otherwise ignore (Source 1).
This is why simply holding your breath is not a strategy. CO2 leaves your body continuously and disperses widely, so the signal is almost always present for a searching mosquito to find.
Body heat and moisture: the mid-range and close-range cues
Once a mosquito is near a potential host, warmth becomes a powerful draw. Mosquitoes are strongly attracted to surfaces around human body temperature, and in controlled tests they preferred warm targets (near 37 degrees Celsius) over cooler ones. Notably, this thermal preference held up whether or not CO2 was present, which suggests heat-seeking runs on its own track once the insect is close (Source 2).
Heat works only over a short range. In the Caltech experiments, mosquitoes began responding to a warm object at a distance of less than about one meter (Source 2). Alongside heat, the humidity and moisture given off by skin help mark a living body against the drier air around it. Heat and moisture together confirm that a target is a real host rather than a random dark object.
Skin odor: the strong short-range attractant
Up close, your personal scent takes over, and it is one of the most decisive cues. Human skin produces a mix of compounds, and research points to carboxylic acids as central to why mosquitoes lock onto people. In a multi-year study, individuals who were most attractive to mosquitoes consistently produced higher levels of these skin-derived carboxylic acids, and this difference stayed stable over time (Source 3).
Mosquitoes sense these acids using a family of odor-detecting ion channels tied to the Ionotropic Receptor (IR) genes. When researchers disabled key IR co-receptors, the mosquitoes were badly impaired at tracking human scent, yet they could still tell a highly attractive person from a weakly attractive one, a sign that the system has built-in redundancy (Source 3).
Skin odor is also the main reason two people sitting side by side get bitten at very different rates. For a closer look at what makes some bodies more of a target, see why some people get bitten more.
Vision and the final approach
Between smelling you and touching down, a mosquito uses its eyes. In the Caltech work, a plume of CO2 made mosquitoes far more likely to fly toward dark, high-contrast objects that they would otherwise pass by. Vision came into play at roughly 5 to 15 meters, bridging the gap between the long-range CO2 signal and the short-range heat cue (Source 2).
The sequence matters. Carbon dioxide says a host is somewhere nearby, vision points the mosquito at a likely shape, and heat and odor confirm the landing spot. This is why wearing dark clothing can make you a more obvious visual target once a mosquito is already searching in your area (Source 2).
Why repellents work
Repellents do not usually poison or kill mosquitoes. They interfere with this chain of cues so the mosquito cannot complete the sequence. Compounds such as DEET appear to act on more than one part of the system: they can jam or mask the odor receptors a mosquito uses to read human scent, and on contact they trigger taste and touch-sensing neurons that make skin unappealing to bite (Source 4).
Because the cues are layered, effective protection focuses on the parts you can control, mainly your skin odor signature and the surface of your skin. Public-health agencies recommend repellents registered with the Environmental Protection Agency, including those with DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone, applied according to the label (Source 5). For product choices and how to use them, see the repellents guide below.
Sources
- McMeniman CJ, Corfas RA, Matthews BJ, Ritchie SA, Vosshall LB. “Multimodal integration of carbon dioxide and other sensory cues drives mosquito attraction to humans.” Cell, 2014. (Peer-reviewed study, Vosshall lab; shows CO2 detection gates responses to heat and lactic acid.) https://pubmed.ncbi.nlm.nih.gov/24581501/ Accessed 2026-07-20.
- van Breugel F, Riffell J, Fairhall A, Dickinson MH. “Mosquitoes use vision to associate odor plumes with thermal targets.” Current Biology, 2015 (Dickinson lab, Caltech). (Peer-reviewed study; reports CO2 detection at roughly 10 to 50 meters, vision at 5 to 15 meters, and heat at less than about 1 meter.) https://www.caltech.edu/about/news/mosquitoes-use-smell-see-their-hosts-47338 Accessed 2026-07-20.
- De Obaldia ME, Morita T, Vosshall LB, et al. “Differential mosquito attraction to humans is associated with skin-derived carboxylic acid levels.” Cell, 2022. (Peer-reviewed study, Vosshall lab; links high carboxylic acid output to strong, stable mosquito attraction.) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10069481/ Accessed 2026-07-20.
- “The mysterious multi-modal repellency of DEET.” PMC (National Institutes of Health). (Peer-reviewed review; describes DEET acting on odorant receptors and on contact chemosensory neurons.) https://pmc.ncbi.nlm.nih.gov/articles/PMC4594586/ Accessed 2026-07-20.
- “Preventing Mosquito Bites.” Centers for Disease Control and Prevention (CDC). (Public-health guidance; lists EPA-registered repellent active ingredients.) https://www.cdc.gov/mosquitoes/prevention/index.html Accessed 2026-07-20.
Related
- Why some people get bitten more (placeholder)
- How to choose and use an insect repellent (placeholder)
- Mosquito anatomy and senses (placeholder)
This page is an educational reference and is not medical or pest-control advice. It summarizes peer-reviewed research and public-health guidance for general understanding.
Last reviewed 20 July 2026.