The question of why biting insects, such as mosquitoes, target some people over others has been extensively explored by science. Insect attraction is not random chance, but a sophisticated sensory process guided by chemical and physical signals that mammals constantly emit. A person’s attractiveness is determined by how their unique biological profile interacts with these highly tuned insect senses. This involves long-range detection, individual body chemistry, and external factors.
How Insects Detect Your Presence
The long-range beacon signaling human presence to insects is the plume of carbon dioxide (\(\text{CO}_2\)) we exhale. Specialized olfactory receptors on a mosquito’s maxillary palp allow them to detect this gas from up to 100 feet away, guiding them toward a potential host. \(\text{CO}_2\) emission is directly related to a person’s metabolic rate. Individuals breathing more heavily, such as those who have recently exercised or are pregnant, are inherently more detectable targets.
Once the insect is closer, thermal and visual signals come into play. Mosquitoes sense the infrared radiation emitted by skin, which acts as a heat signature to help them pinpoint a landing spot. This thermal detection is combined with visual cues, where movement and high-contrast objects help the insect confirm the location of their host. The combination of \(\text{CO}_2\), heat, and movement creates a compelling signal that tells the insect a warm-blooded meal is nearby.
Individual Differences in Skin Chemistry
Differences in attraction stem from the unique cocktail of volatile organic compounds (VOCs) on a person’s skin. The skin hosts a diverse community of bacteria known as the skin microbiome. These microbes consume non-odorous compounds in sweat, such as amino acids and fatty acids. They convert these into the specific VOCs that constitute human body odor.
The composition of the skin microbiome varies significantly due to genetics, diet, and environment. This variation results in an individualized scent profile. Certain compounds produced by microbial activity, such as lactic acid, ammonia, and specific carboxylic acids, are highly attractive to mosquitoes. Individuals whose microbiomes produce higher concentrations of these compounds are consistently more attractive. Lactic acid concentration often increases after strenuous activity, making it a strong attractant when combined with \(\text{CO}_2\) and other skin volatiles.
Genetic factors also play an indirect role in attraction by influencing the makeup of the skin microbiome and the chemical secretions in sweat. For instance, a person’s blood type may influence their attractiveness, as about 85% of people secrete chemical signals through their skin that indicate their blood type. Studies have suggested that individuals with Type O blood are significantly more likely to be bitten than those with Type A, with Type B falling in the middle, although the exact mechanism for this preference is still being investigated.
External Factors That Increase Attraction
Beyond internal biology, external factors can increase an individual’s appeal to insects. Clothing color is a visual element insects use to select a target, often preferring dark colors like black, navy blue, and red. Dark shades absorb more heat, creating a warmer thermal target, and stand out more visually. Conversely, light colors such as white or green are less attractive because they reflect more light and heat.
Applied scents can also draw insects closer, as perfumes, scented lotions, and hair products often contain floral or fruity fragrances. These scents mimic nectar, a primary food source for many insects, including mosquitoes and bees. Using highly fragrant personal care products can confuse insects and attract them for investigation.
The consumption of alcohol, particularly beer, increases a person’s attractiveness to mosquitoes. Alcohol intake raises body temperature and increases the concentration of ethanol and other volatile compounds in the sweat and breath. These physiological changes create a more compelling set of cues for insects, making the person easier to locate and more appealing.