If you have ever sat next to someone at an outdoor event and received far more mosquito bites while they walked away unaffected, you may have assumed it was bad luck. The reality is more scientifically interesting: mosquitoes respond to biological signals, and some people emit stronger signals than others. Here is what the research actually shows — and what it means for your summer protection strategy.

Carbon Dioxide: The Primary Long-Range Signal

Mosquitoes can detect carbon dioxide — the gas humans exhale with every breath — from considerable distances. CO₂ is the primary long-range cue mosquitoes use to identify that a potential host is nearby.

People who exhale more CO₂ are detectable from farther away and are more frequently targeted. Factors that increase CO₂ output include larger body size, higher levels of physical activity, and pregnancy. This is one reason children are sometimes less frequently targeted than adults in the same group — smaller bodies produce less CO₂.

Body Heat

In addition to CO₂, mosquitoes navigate by detecting heat. People who naturally run at higher body temperatures, or who have been physically active recently, present a stronger heat signature that mosquitoes can detect at close range.

This also explains a pattern you may have noticed: mosquitoes tend to move toward areas of bare, warm skin rather than landing anywhere at random. They are navigating toward the strongest heat source once they have already located a host through CO₂.

Lactic Acid and Sweat Composition

Physical activity increases lactic acid production, which is released through perspiration. Lactic acid is detectable by mosquitoes and has been documented as an attractant in research literature. Sweat composition also varies considerably between individuals — some people produce chemical compounds that mosquitoes respond to more readily than others.

This is part of why you may notice more bites after exercise, and why some people in the same outdoor group receive more mosquito bites while others go largely unbothered by comparison.

Why Mosquitoes Become More Active at Dusk

Many mosquito species found in Southern California — including Culex mosquitoes, the primary West Nile Virus vector in our region — are most active from dusk through the night. Cooler temperatures, lower wind speeds, and reduced sunlight create conditions that help mosquitoes conserve moisture while searching for hosts.

Culex mosquito activity pattern. Source: American Mosquito Control Association.

Planning outdoor activities earlier in the day — or applying repellent before evening gatherings — is one of the most practical ways to reduce your exposure during the hours when mosquito activity is highest.

Clothing Color: What a 2022 Study Found

In 2022, researchers at the University of Washington published a study in Nature Communications examining how Aedes aegypti mosquitoes respond to visual color cues. After being exposed to carbon dioxide, mosquitoes showed a preference for flying toward certain colors — black, red, orange, and cyan — while largely ignoring green, blue, white, and purple.

Wearing lighter-colored clothing in the evening may reduce how visually noticeable you are after mosquitoes have already detected you through carbon dioxide and body heat. It is a small but scientifically grounded supporting measure — not a substitute for repellent.

Source: Egizi, A.M., et al. (2022). Mosquito visual preference. Nature Communications. University of Washington.

What About Blood Type?

Some studies have explored this question, but results across the research literature are inconsistent. We do not recommend blood type as a framework for personal mosquito protection decisions.

What You Can Actually Do

Understanding why you are targeted does not change the need for protection — but it does help clarify which measures are most effective. The following recommendations are grounded in the strongest available evidence.

• Apply an EPA-registered repellent to all exposed skin before going outside. Oil of Lemon Eucalyptus (OLE) is a plant-based option recommended by the CDC for protection against mosquitoes that may carry West Nile Virus. Visit epa.gov/insect-repellents to find the right product for your household. Repellent is the most reliable protection available regardless of your individual biology.
• Time your outdoor activities — Culex mosquitoes are most active from dusk through the night. If you notice you tend to receive more bites than those around you, reducing unprotected evening exposure is a meaningful step.
• Wear lighter-colored clothing in the evening — a small reduction in visual targeting, most effective when combined with repellent.
• If you have been exercising or sweating before spending time outdoors, showering and changing into clean clothes may help reduce some of the scent cues mosquitoes use to locate hosts.
• Eliminate standing water near your home — reducing the local mosquito population means fewer mosquitoes tracking anyone in your household. Flower pot trays, gutters, bird baths, and garden areas where water pools are the most common residential breeding sources.