Why mosquitoes love some people more than others — and why it's probably not 'sweet blood'

Some people seem to emerge from a winter evening covered in itchy bites while those around them escape almost untouched. Scientists say the difference is real, but it has little to do with the long-held belief that mosquitoes prefer people with "sweet blood."

Instead, researchers say so-called "mosquito magnets" owe their appeal to a complex combination of body chemistry, skin bacteria, genetics and even body heat—factors that can make one person dramatically more attractive to mosquitoes than another, says the BBC.

Following an invisible trail

Only female mosquitoes bite humans because they need the protein in blood to produce eggs. They can detect people from as far as 10 metres (33 feet) away by following what scientists describe as a cascade of cues, beginning with carbon dioxide (CO2) and ending with the unique chemical signature produced by each person's skin.

That helps explain why adults are generally bitten more often than children—they simply produce more CO2. Pregnant women are also especially attractive to mosquitoes because they exhale more CO2 and have slightly higher body temperatures, making them about twice as likely to attract bites. A workout can have a similar, though temporary, effect by increasing body heat and sweat.

The chemistry of a mosquito magnet

The biggest clue, however, lies much closer to the skin.

Humans carry a unique blend of more than 500 volatile organic compounds (VOCs), created when naturally occurring bacteria on the skin break down substances such as fatty acids. This invisible chemical fingerprint varies from person to person, allowing mosquitoes to distinguish between potential hosts.

Among the strongest attractants are compounds known as carboxylic acids. Researchers found that people with higher levels of these chemicals on their skin were dramatically more appealing to mosquitoes because the acids enhance the attraction of other compounds, including ammonia and lactic acid.

In one study, the most attractive volunteers ranked 100 times higher on a mosquito attractiveness scale than the least attractive participants, with mosquitoes consistently choosing odours from people with higher levels of carboxylic acids.

Born to be bitten?

The findings also suggest that being a mosquito magnet is not something most people can easily change.

Scientists found that a person's attractiveness to mosquitoes remains remarkably consistent over several years, regardless of lifestyle changes. Studies involving twins further suggest that the body odours responsible for "bite-ability" are partly inherited, with identical twins showing similar levels of attractiveness while non-identical twins differed.

The bacteria living on the skin also play a role. People who receive more bites tend to have bacterial communities that are more abundant but less diverse, shaping the chemical cocktail that mosquitoes detect.

It's not always more bites

Not everyone who thinks they are a mosquito magnet is necessarily getting bitten more often.

Researchers say genetics also influence how the immune system responds to mosquito saliva. Some people develop larger, itchier welts than others, making the bites far more noticeable even if the number of bites is similar.

What actually works

As for popular home remedies, the evidence is less convincing. Researchers say claims that eating garlic or taking vitamin B tablets can ward off mosquitoes have only minimal or unclear scientific support.

For now, the best defence remains the simplest: use insect repellents containing DEET, picaridin or PMD, wear long sleeves and trousers—especially those treated with insecticide—and reapply protection regularly, particularly after sweating.

For those who consistently attract mosquitoes wherever they go, the science suggests the insects are responding to biology rather than bad luck.