Why Mosquitoes Bite Some People and Not Others -- And the Surprising, Natural Way to Avoid Bites
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Why are some people so much more attractive to mosquitoes than others? And what can you do about the pesky little bloodsuckers, especially if you don’t want to resort to DEET? (DEET, while effective, is also weakly neurotoxic in humans.)
To start, there are some 150 different species of mosquitoes in the United States, and they differ in biting persistence, habits, ability to transmit disease, and even flying ability.
Mosquitoes of the genus Culex are painful and persistent biters and they will gladly fly into your house to bite you. They bite at dusk and after dark, and they can spread West Nile virus. On the upside, however, they are not strong fliers and won’t fly long distances from where they hatched. And, they’d prefer to bite a bird than a human. A common Culex species in the U.S. is C. pipiens, the Northern House mosquito.
Then there’s the genus Aedes, which includes A. aegypti and A. albopictus, the Asian Tiger mosquito. The former is not a problem in the U.S.; the latter is. Both can transmit Yellow Fever and Dengue Fever. Aedes mosquitoes feed early in the morning as well as at dusk and into the evening. They might also bite you during the day if it’s cloudy or if you wander into a shady place. Fortunately, they probably won’t enter your house – but they do prefer biting mammals like humans over other animals, and they are very strong fliers.
One other notable genus of mosquitoes are Anopheles mosquitoes. They are the ones responsible for transmitting malaria. In the U.S., that mostly means A. quadrimaculatus, which lives in the central and eastern U.S., as far north as southern Canada.
But if we have Anopheles mosquitoes, then why don’t we have malaria? The answer, in part, is due to climate. According to Andrew Githeko, a Kenyan scientist who studies malaria, malaria only occurs in places where the average temperature is above 18C (64.4F). Below that, the mosquito dies before the parasite matures, and this prevents transmission. In Kenya, he discovered malaria already moving into new areas as the climate warmed. Fortunately, malaria is not endemic to the U.S. as it is in Kenya. And if the U.S. lacks a base of humans and mosquitoes carrying the parasite, then that prevents the spread of the disease.
These different genera and species not only differ in the ways listed above; they also differ slightly in what attracts them to hosts they wish to bite. Mosquitoes use carbon dioxide, heat, moisture, scent, and even vision to locate hosts. When they are sniffing us out, they home in on a large number of chemicals. A 2000 study identified 346 chemicals from human hand odors, of which 277 were potential mosquito attractants.
The most significant chemicals mosquitoes use to locate us and bite us include l-lactic acid, ammonia, carboxylic acids, and octenol, in combination with one another. In experiments, scientists found that adding l-lactic acid to the scent of an unattractive person made them more attractive to Aedes aegypti mosquitoes, and vice versa. Additionally, the presence of carbon dioxide makes A. aegypti mosquitoes more sensitive to human skin odors.
A 1999 study found that malarial mosquitoes were not attracted to fresh human sweat, but found attractive after it was incubated for one or two days. During the two days, bacteria in the sweat multiplied and the pH changed from acidic to alkaline, signifying a decomposition of sweat components into ammonia. The study also notes that malarial mosquitoes flock to the scent of limburger cheese, which resembles human foot odor. Githeko confirms that, indeed, malarial mosquitoes are attracted to chemicals produced by bacteria on one’s feet, and they will even bite a pair of smelly socks if you hang them up after wearing them for a few days.