Sitting beside someone who remains untouched while you become an insect feeding ground suggests biting insects have distinct preferences. This differential attraction is not random but is rooted in measurable biological and physical factors that make certain individuals more detectable. Female mosquitoes bite to obtain the protein needed for egg development, employing a sophisticated, multi-stage tracking system to locate a blood meal. Your body chemistry, genetics, and even clothing choice combine to create a unique signal that insects can interpret from a distance.
Metabolic Factors and Chemical Signals
The initial and most significant signal a host emits is carbon dioxide (CO2), which mosquitoes can detect from over 50 feet away. This gas is an unavoidable byproduct of human respiration and metabolism, serving as the universal beacon indicating a warm-blooded animal is nearby. Individuals with a higher metabolic rate naturally exhale more CO2, making them a larger and more easily identifiable target.
Increased CO2 output occurs during periods of physical activity, such as exercise, or due to physiological states like pregnancy, both of which raise the body’s overall metabolic activity. Once the insect detects the CO2 trail, it seeks secondary chemical signals that confirm the host’s presence. These secondary cues are volatile organic compounds (VOCs) released through the skin and sweat.
Among the most attractive compounds is lactic acid, produced when the body metabolizes glucose during exertion or when bacteria break down sweat. Other sweat-related compounds also form part of the chemical “cocktail” that a mosquito’s specialized antennae can detect. The specific blend and concentration of these VOCs in a person’s exhalation and sweat create a unique chemical fingerprint that determines their attractiveness.
The Role of Skin Microbiome and Blood Type
The distinct chemical profile that draws insects is influenced by the unique population of bacteria residing on a person’s skin, known as the skin microbiome. These microorganisms break down compounds in sweat and sebum into volatile molecules, some of which are highly attractive to mosquitoes. Even between two people, the composition and density of their skin bacteria differ significantly, leading to a variance in resulting odors.
Studies show that individuals with a higher diversity but lower total abundance of certain bacterial species, such as those that produce high levels of L-(+)-lactic acid, tend to be more attractive. Common skin microbes, like certain strains of Staphylococcus and Corynebacterium, are effective at generating these appealing scents. This means one person’s skin ecology may produce an odor that a mosquito perceives as a rich food source, while another person’s microbiome yields less appealing compounds.
Beyond skin odors, blood type also plays a role in host preference. Research suggests that mosquitoes prefer people with Type O blood compared to other types. This preference is linked to secretor status, a genetic trait where approximately 80% of people secrete water-soluble antigens corresponding to their blood type through their skin. A Type O secretor emits a chemical signal that mosquitoes can detect, indicating the presence of their preferred blood type beneath the skin surface.
Physical Attraction: Heat, Movement, and Color
Once a mosquito has closed the gap using chemical cues, it relies on physical signals to make its final approach and choose a landing spot. Body heat detection is a primary thermal cue, which mosquitoes sense from a short distance using specialized receptors. Warmer body temperatures—whether due to a naturally higher core temperature, recent exercise, or a fever—make a person easier to locate and target.
Movement is another physical attractant, serving as a visual cue that signals the presence of a live, mobile host. A moving target is more easily spotted than a stationary one, especially as the insect approaches. The combination of motion and increased CO2 output from exertion creates a potent double signal for a foraging mosquito.
The color of clothing influences a mosquito’s visual perception and landing decision. Dark colors, such as black, navy blue, and red, stand out more prominently and absorb heat more effectively than light colors. Since mosquitoes are drawn to objects that are both visually distinct and slightly warmer, wearing darker attire can increase a person’s visibility and attractiveness.