It's a balmy Saturday night in October. Snags are sizzling on the barbecue, the sun is setting and the laughter is getting louder.
Then you feel it.
One mosquito bite on your ankle, three on your arm and another on the back of your neck.
Your friend, on the other hand, has none.
Now, a group of American researchers say they have part of the answer explaining why.
In a new research paper, released today, scientists from Rockefeller University found mosquitoes are drawn to people who secrete an odour on their skin caused by a mix of naturally occurring acids.
The scientists focused on the Aedes aegypti mosquito, which carries viruses that cause serious diseases such as yellow fever, dengue and Zika.
As part of their three-year study, the scientists carried out more than 2,330 tests over 174 days using samples of human forearm odour collected on nylon sleeves.
They found people who get ravaged by mozzies secrete significantly higher levels of ‘carboxylic acids’ from their skin than others, citing genetics as a factor.
"We tested mosquito attraction to human skin odour and identified people who are exceptionally attractive or unattractive to mosquitoes," the researchers wrote.
"Chemical analysis revealed that highly attractive people produce significantly more carboxylic acids in their skin [than others]."
The researchers suggested genetics may play a role in determining a person's skin acid composition, and their susceptibility to getting bitten around a barbecue.
"Understanding why some humans are more attractive than others provides insights into what skin odorants are most important to the mosquito and could inform the development of more effective ... repellents," the paper said.
Many reasons driving mozzie bites
It's not the first time scientists have tried to decipher why some people get attacked by mozzies and others are left untouched.
Dr Cameron Webb, a mosquito researcher at the University of Sydney, said there were lots of reasons why someone might get bitten by mosquitoes more than another.
"It can be to do with your genetics, and how that determines the mix of chemicals on your skin," he said.
"But also your activity, whether you're hot or cold, sweaty, pregnant, and maybe to a certain extent, your diet."
Dr Gordana Rasic, a senior mosquito research officer at QIMR Berghofer Medical Research Institute in Queensland, said scientists recently found people who have been infected with malaria suddenly became more attractive to mosquitoes.
"This has very important implications because if an infected person gets bit, then the mosquito gets infected and then transmits malaria so it's a vicious cycle," she said.
Dr Rasic said the influences driving mosquito behaviour were "very complex".
"Mosquito brains are small but they still process signals from hundreds and hundreds of different receptors," she said.
"Biting humans is specific to female mosquitoes — they need to bite humans and take blood in order to develop their egg and basically reproduce — so it's an absolutely essential instinct."
Dr Webb also pointed out that the American researchers focused on one mosquito species, the yellow fever or dengue mosquito, when "there are thousands of mosquito species around the planet".
"Even if you solve the problem for one mosquito, that doesn't mean the relationship and their willingness to bite people applies to all of the mozzies," he said.
The dengue mosquito carries a virus that causes dengue fever, which has similar symptoms to a severe case of the flu.
It was a big problem in Australia in the years after World War II, but is not usually present today except for outbreaks in north and central Queensland.
In March last year, a dengue mosquito was detected in the remote Northern Territory town of Tennant Creek, according to NT Health.
One has also been detected in Groote Eylandt.
Climate change likely to increase mozzie risk
Although the dengue mosquito is not widespread in Australia today, Dr Webb said climate change would likely increase the risk of mosquito-borne diseases in Australia in coming years.
A recent example was the spread of Japanese encephalitis, he said.
Since reaching Australia in March, the virus has been detected in humans, pigs and mosquitoes across South Australia, Victoria, New South Wales, Queensland and Northern Territory.
There have been 40 cases of human disease, including six deaths.
"One of the reasons why we think this virus has not only got to Australia, but particularly why it has spread so widely, is because we've had two years of non-stop rain across the country," Dr Webb said.
"La Niña brings lots of water to the environment and that provides a great habitat for mosquitoes, but it also provides a great habitat for the wildlife that are reservoirs for the virus as well... such as waterbirds."
Dr Webb said extreme weather events such as cyclones and flooding could also make the local environment "much more productive for mosquitoes".
