Two people can spend the same night in the same backyard and end up with very different experiences: one barely notices the insects; the other accumulates bites. The explanation is not a single characteristic, such as "sweet blood" or just blood type. Mosquitoes search for hosts by combining chemical and physical signals, and the importance of each clue changes depending on the species and the moment of approach.
The most consistent evidence to explain why one person attracts more mosquitoes than another points to body odor, especially the mixture of volatile compounds released by the skin. CO₂, heat and visual cues help the mosquito go into search mode, locate a possible host and get closer. Blood type has some experimental evidence, but it is much more limited and specific than the "type O attracts mosquito" reputation suggests.
CO₂ helps find a host, but doesn't tell the whole story
When we breathe, we release carbon dioxide. For several mosquito species, encountering a CO₂ plume changes behavior: the insect increases its searching activity and responds more strongly to other cues associated with a host.
Experiments with Aedes aegypti clearly show this integration. In a study published in Nature Communications in 2022, the presence of CO₂ was decisive in activating attraction to visual targets; Without this signal, mosquitoes practically did not investigate objects in the same way. In work published in Nature in 2024, Aedes aegypti also combined CO₂ and human odor with infrared radiation associated with body heat during search.
This puts CO₂ in an important position, but different from the idea that it alone defines who will be stung the most. The gas indicates that there is an animal breathing nearby and helps organize the search. To distinguish between two close people, however, the skin's chemical signature can provide much more specific information.
Skin smell is one of the strongest clues to explain differences between people
"Smell" here doesn't just mean what the human nose perceives as sweat or perfume. The skin releases a complex mixture of volatile molecules, in proportions that vary from person to person. Mosquitoes have olfactory systems capable of detecting part of this mixture.
A study published in Cell in 2022 followed volunteers with persistent differences in attraction to Aedes aegypti. The more attractive participants had higher levels of certain carboxylic acids in their skin emanations. The association was stable over time, although the study itself did not demonstrate that a single molecule alone explains the preference.
This detail is important. The idea of a "magic compound" that turns someone into a mosquito magnet is tempting, but the data points to combinations. Another 2026 study, published in iScience, analyzed the body odor of 42 women and identified 27 volatile organic compounds potentially related to attractiveness. In behavioral tests, both the presence of 1-octen-3-ol in certain profiles and the proportion of compounds in the mixture changed the mosquitoes' preference.
In other words, the mosquito doesn't seem to read a simple chemical label. He responds to a profile.
The skin microbiome participates because it also changes the odor
Part of what we call body odor arises from the interaction between skin secretions and microorganisms that live on it. Therefore, two people can have different chemical profiles even when they are in the same environment and without using perfumes.
In 2011, a study with Anopheles gambiae showed that the composition of the skin's microbiota was related to the attractiveness of volunteers to this species. People classified as highly attractive had, in that experiment, a greater abundance and lower diversity of bacteria compared to unattractive participants.
The conclusion should not be turned into a "more bacteria = more bites" rule. The result was obtained with one species and within a specific experimental design. What remains relevant is the overall mechanism: the microbiome helps form the skin's odor cloud, and this cloud can alter the mosquito's response.
The most recent research precisely reinforces the need to think about specific combinations. In 2026, researchers measured 119 participants' attraction to Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus. The three species generally did not prefer the same people, and patterns of attraction were associated with different odor signatures and skin bacteria.
Mosquito species changes who looks more attractive
This is one of the points that most dismantles the notion of "a person who always attracts mosquitoes". In the 2026 study of 119 participants, the same person could be relatively attractive to one species and unattractive to another.
Researchers have found different relationships between odor compounds and attraction. Aedes aegypti and Culex quinquefasciatus were associated, for example, with the absence of certain odors
potentially repellent, while Aedes albopictus showed an association with the presence of other compounds, such as ketones. Bacterial signatures also varied between species.
This means that the question "why do mosquitoes choose me?" needs a correction: which mosquitoes? Aedes aegypti, Aedes albopictus, Culex and Anopheles are not sensory copies of each other. They share important clues, but they can be given different weights.
The practical consequence is that, based on current evidence, there is no human profile that is universally irresistible to all mosquitoes.
Heat and infrared help with approach
Mosquitoes also exploit thermal information. The human body creates heat gradients and emits infrared radiation. In 2024, researchers showed that Aedes aegypti uses thermal infrared as a directional cue when this signal appears alongside CO₂ and human odor.
The point is not that the insect "sees heat" like a thermal camera. The study proposes a sensory mechanism in which radiation heats structures at the end of the antenna and activates receptors linked to temperature. This helps explain how the mosquito improves navigation when already looking for a host.
For this reason, heat makes more sense as part of an approximation system than as an isolated explanation for differences between people. A warmer person at a given moment may provide a stronger physical cue, but the mosquito continues to integrate that information with odor, CO₂, and other cues.
Vision also comes into play, but it depends on the context
The classic image that "mosquitoes like dark clothes" contains part of the story, but it is simplified. Mosquitoes use vision to locate objects and contrasts, and the visual response can be activated or modulated by smell.
In the 2022 study of Aedes aegypti, CO₂ strongly increased attraction to certain wavelengths, including bands that correspond to the orange and red present in the spectrum reflected by human skin. The researchers also noted that visual preferences can vary between species.
This doesn't mean that wearing a specific color determines who gets stung between two people. The visual cue helps the insect locate a target in a real scenario; the final choice depends on the set of signals.
What about blood type O?
The relationship between mosquitoes and the ABO system exists in the literature, but it is much less solid than it usually appears in lists of curiosities.
A 2004 study evaluated 64 volunteers and counted Aedes albopictus landings on their forearms. Type O people received more landings, on average, than participants in the other groups, but the statistically significant difference occurred only in the comparison between O and A. The work itself was unable to explain the preference only for the ABO antigens tested.
There are two problems with turning this result into a rule. First, the experiment studied a specific species. Second, landing and attraction are behaviors influenced by
many other clues present on the volunteer's skin. The ABO system may contribute in certain conditions, but does not occupy the same level of evidence as body odor and sensory integration.
Therefore, "mosquitoes prefer type O blood" is too strong a phrase. The most defensible is to say that there is limited evidence of an association between blood type and attraction in some experiments, with no demonstration that type O makes someone a universal target.
Why two people side by side can have such different results
Imagine two people in the same environment. Both breathe and provide CO₂, both emit heat and both are visually detectable. What begins to separate them is the fine combination of signals: which compounds come out of the skin, in what proportion, which microorganisms participate in this chemistry and how the species present interprets this set.
The difference observed later can still be amplified by exposure factors: area of uncovered skin, movement, position in relation to the wind, time of activity of the species and presence of barriers or repellents. Therefore, counting bites at the end of the night is not a pure test of "biological attractiveness".
Laboratory studies attempt to separate some of these variables using olfactometers, odor-smelling nylon sleeves, wind tunnels and controlled arenas. Still, measuring attraction isn't quite the same thing as measuring actual bites. The 2026 study of 119 people, for example, compared attraction responses to human odors; he did not demonstrate that each participant would receive the same order of bites in an everyday situation.
What the hierarchy of evidence allows us to affirm
If the question is which factor deserves more weight, skin odor and its chemical composition are among the strongest explanations for persistent differences between people. The microbiome matters because it participates in the production of this signature. The species of mosquito is decisive because different species can classify the same person in different ways.
CO₂ is a central cue to initiate and guide the search, while heat, infrared and vision refine the approach and location of the target. They all work better as parts of an integrated system than as independent causes.
Blood type is lower in this hierarchy. It may have an effect in certain species and conditions, but it does not robustly explain why a person always appears "sweeter" to mosquitoes.
The answer most faithful to the evidence, therefore, is less intuitive and more interesting: some people are indeed more attractive to certain mosquitoes, but this preference arises from a combination of smell, microbiome and physical cues interpreted by a specific species. There is no single factor that turns someone into a universal magnet.
