Why Mosquitoes Bite Some People More Than Others
One person leaves a balcony dinner with eleven bites and the other with none. This is a real and repeatable difference rather than an impression, and it has been studied enough to say something useful about it.
What it is not is sweet blood, which is the explanation everybody offers and which has no meaning physiologically.
Carbon dioxide is the long-range signal
Mosquitoes detect exhaled carbon dioxide from a considerable distance and use it to locate a host. Anyone exhaling more is more detectable: larger people, pregnant women, and anyone who has just exercised or is breathing hard.
This is the largest single factor and it is almost entirely outside your control, which is worth knowing before spending money on things that address the smaller ones.
Body heat and moisture, close up
Once nearby, mosquitoes home in on warmth and humidity. A warm, slightly damp person is a much clearer target than a cool dry one, which is why sitting still under a fan in an air-conditioned room genuinely reduces bites and why the person who has just walked in from outside gets bitten first.
Pregnancy raises both body temperature and exhaled carbon dioxide, which is why pregnant women are consistently bitten more and why mosquito protection matters more during pregnancy in a dengue-endemic city.
Skin chemistry
The mix of compounds produced by skin bacteria varies substantially between people, and some combinations are markedly more attractive than others. Lactic acid, ammonia and various fatty acids are among the compounds involved.
That composition is largely genetic and stable, which is the honest reason one member of a household is bitten more than the rest. It is not diet, and there is no reliable way to change it.
Blood type, briefly
Some studies have found a preference for type O in laboratory settings. The effect, where found, is modest compared with carbon dioxide and body heat, and it is not something to plan around. It is also not something you can change, which makes it interesting rather than useful.
What does not work
Vitamin B1 tablets have been tested repeatedly and have no effect. Eating garlic has no measurable effect. Marmite and similar have no effect. Mosquito-repelling plants sitting in a pot release almost nothing into the air.
Ultrasonic repellent devices and phone applications do nothing, and this has been tested more often than almost any other claim in this field.
What genuinely reduces bites on a person
A topical repellent containing DEET, picaridin or oil of lemon eucalyptus, applied as directed, is the measure with real evidence behind it. Concentration affects duration rather than effectiveness, so a lower concentration applied more often works as well as a higher one for most situations.
Beyond that: loose clothing covering arms and ankles, a fan, and avoiding the peak activity windows. A fan is more effective than it sounds, because mosquitoes fly poorly in moving air and because it disperses the carbon dioxide plume that draws them in.
Clothing colour has a modest real effect that is often overstated. Mosquitoes use visual contrast at close range and are drawn to darker shapes against a lighter background, so dark clothing is marginally worse than pale. It is a small factor next to carbon dioxide and heat, and it is worth mentioning mainly because it is one of the few popular beliefs in this area that is not simply wrong.
Why some people react more visibly
Two different things are being conflated when people compare bites. One is how often you are bitten; the other is how strongly your immune system reacts. Somebody who reacts strongly notices every bite as a large itchy welt, while a person who has been in the region for years often reacts far less and may not notice bites at all.
This is why long-term residents frequently believe they are bitten less. Sometimes they are, through desensitisation of the reaction rather than through any change in attractiveness — which matters, because it means they are equally exposed to anything the mosquito carries.
Related reading
See Aedes and Culex compared and our mosquito guide. On sources, breeding sites around your home and balcony planters. For claims that do not hold, do plants repel mosquitoes and things that do not work. Our parent company runs the Vietnamese-language mosquito control programme.
Global Pest Control is the English-language arm of Khử Trùng Toàn Cầu, based in Thu Duc City.
Common questions
Is DEET safe to use every day?
It has been in use for decades and is regarded as safe when applied according to the label, including for children above the age stated on the product. Follow the concentration guidance for children, apply to exposed skin rather than under clothing, and wash it off when you come indoors. For anyone uncertain, picaridin is an alternative with a similar evidence base.
My partner is never bitten. Should we stop using repellent?
No. Being bitten less is not the same as being protected, and the person who is rarely bitten is still exposed when a mosquito does bite. In a city where dengue is present every year, the sensible approach is protection for the household rather than for whoever notices the bites.
Do bites get worse the longer you live here?
Usually the opposite. Repeated exposure tends to reduce the visible reaction over months and years, so long-term residents often stop noticing bites. The bites still happen, which is the part worth remembering — a reduced reaction is not reduced risk.
