CO2 Emitted by Men and Women: Why Does It Attract Mosquitoes?

# CO2 Emitted by Men and Women: Why Does It Attract Mosquitoes?

You may have noticed that some people seem to attract mosquitoes like magnets, while others spend the entire evening without a single bite. Behind this mystery lies a fascinating biological reality: mosquitoes are chemical hunters of remarkable precision, and the carbon dioxide (CO2) we exhale with every breath is their primary long-range detection signal. But why exactly? And are there differences between men and women in this mechanism? Here is everything science knows on the subject.

How Do Mosquitoes Detect CO2?

Female mosquitoes — the only ones that bite, since they need blood proteins to develop their eggs — possess a sensory organ of remarkable sophistication: the maxillary palp. This appendage, located on either side of their proboscis, is covered with specialized olfactory receptors called cpA neurons (CO2-sensitive neurons).

These neurons can detect CO2 concentrations as low as a few tens of parts per million (ppm) above the ambient air level (approximately 400 ppm). In practical terms, this means a mosquito can detect the CO2 plume you exhale at distances of up to 50 meters under favorable conditions — calm wind, humid air, dense vegetation.

Once it detects this chemical signature, the mosquito follows the concentration gradient, much like a hunting dog follows a scent trail, until it locates its source. This is called positive anemotaxis: flight behavior oriented toward the source of a wind-borne odor.

Why CO2 Specifically?

CO2 is a universal marker of animal life. All mammals, birds, and reptiles emit it when breathing. For a mosquito, a CO2 plume means one simple and certain thing: a warm-blooded living creature is there, and it can feed me.

This is no evolutionary coincidence. Mosquitoes have developed this CO2 sensitivity over millions of years of co-evolution with their hosts. Laboratory studies have shown that mosquitoes deprived of their CO2 receptors (through genetic manipulation) lose much of their ability to locate a host, even at close range.

But CO2 alone is not enough to trigger a bite. It acts as a long-range alarm signal that puts the mosquito into "active hunting mode." Within one meter, other signals take over.

The Complete Table of Attractive Signals

CO2 is therefore the primary trigger, but it is the combination of multiple signals that determines whether you will be bitten — and how often.

Men vs. Women: Who Emits More CO2?

This is where human biology comes into play in a very concrete way. CO2 production by the body depends directly on basal metabolic rate and muscle mass, two parameters that differ significantly between the sexes.

On average, an adult man at rest produces approximately 200 to 250 ml of CO2 per minute, compared to 160 to 200 ml for an adult woman of similar build. This difference is explained by several factors:

• Men have on average greater muscle mass (muscles consume more oxygen and therefore produce more CO2)
• The male basal metabolic rate is generally 5 to 10% higher than the female
• Men's larger body surface area mechanically increases emissions

Does this mean men get bitten more than women? Not necessarily, as other factors compensate for or amplify this difference.

The Special Case of Pregnant Women

Pregnant women are a special case, documented by several scientific studies. Research published in the British Medical Journal showed that they are twice as likely to be bitten as non-pregnant women. Two main reasons explain this phenomenon:

First, a pregnant woman exhales 21% more CO2 than a non-pregnant woman, due to the increased respiratory volume linked to the metabolic needs of the fetus. Second, the abdominal temperature of a pregnant woman is slightly higher (up to +0.7°C/1.3°F), which increases the emission of volatile skin compounds and strengthens the thermal signal.

This is an important fact for pregnant women traveling to the Caribbean, where the risks associated with vector-borne diseases (dengue, Zika, chikungunya) are real. Enhanced protection is absolutely essential.

Physical Exertion: The CO2 Multiplier

Whether male or female, physical exertion is the factor that most rapidly increases CO2 production. During intense exercise, production can rise from 200 ml/min at rest to more than 4,000 ml/min — a 20-fold increase.

In practical terms, if you go hiking in tropical forest (like those described in our guide to trails in Martinique and Guadeloupe), you emit a considerably stronger CO2 signal than at rest. Add to this sweat (lactic acid, ammonia, octenol), increased body heat, and the dark clothing often worn for hiking — and you understand why hikers are particularly exposed.

Practical tips for athletes and hikers:

• Apply a repellent containing DEET (30–50%) or icaridin before exertion, and reapply after sweating
• Wear light-colored long-sleeved clothing
• Avoid peak mosquito activity hours (dawn and dusk)
• Carry a repellent spray in your backpack for reapplication

Beer and Alcohol: An Unexpected Attractant

A French study published in PLOS ONE revealed a surprising link: drinking just one beer (500 ml) significantly increases a person's attractiveness to mosquitoes. The exact mechanism is not yet fully understood, but two hypotheses are proposed:

On one hand, alcohol slightly increases skin temperature and perspiration, amplifying chemical signals. On the other hand, ethanol and its metabolites may be partially excreted through the skin, adding an additional chemical signal.

If you spend an evening on a terrace in the Caribbean with a ti-punch or a cold local beer, remember to apply your repellent beforehand!

Can You Reduce Your CO2 Attractiveness?

This is the question everyone asks. The honest answer is: you cannot significantly modify your CO2 emissions, as they are directly linked to your metabolism. Holding your breath is obviously not an option.

However, you can mask or neutralize the other signals that amplify the CO2 effect:

• Skin repellents: DEET, icaridin, and IR3535 work partly by blocking mosquitoes' olfactory receptors — they don't "repel" mosquitoes in the literal sense, but prevent them from detecting the chemical signals from your skin
• Permethrin-impregnated clothing: Creates an additional physical and chemical barrier
• Fans and air conditioning: Disperse the CO2 plume and make localization more difficult for mosquitoes
• Mosquito nets: The simplest and most effective solution for sleeping without being bitten

What This Means for Your Caribbean Stay

Understanding the CO2 mechanism allows you to adopt a smarter protection strategy. Here is a practical summary by profile:

Conclusion: Science in Service of Your Protection

CO2 is indeed the primary trigger of mosquito attraction to humans — male or female. But it is a symphony of chemical, thermal, and visual signals that ultimately determines who gets bitten and how many times. The good news is that this scientific knowledge allows us to target our protection efforts where they are most effective.

In the Caribbean, where mosquitoes are active year-round and can transmit dengue, Zika, and chikungunya, this understanding is not merely intellectual curiosity — it is public health information. Protect yourself intelligently, and fully enjoy your vacation or life in the Caribbean.

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To go further, see our article on [mosquito repellents: which one to choose for the Caribbean](/blog/repulsifs-anti-moustiques-comparatif) and our [complete hiking guide for Martinique and Guadeloupe](/randonnees) with mosquito risk levels by trail.