Scientists have revealed why mosquitoes prefer to feast on humans over other animals, and it has a lot to do with our 'citrusy' scent.

A new study published in the journal Nature stated that mosquitoes have evolved to bite humans by exclusively relying on odour molecules distinct from those exuded by other creatures in the surrounding environment.

As reported by The Independent, these Aedes aegypti mosquitoes, which act as vectors for diseases like Zika, dengue and yellow fever, strongly prefer human odour over the odour of animals.

Scientists from the Princeton University in the U.S. applied an approach by imaging mosquito brains at a very high resolution to see how they react to different types of scent.

To achieve this they genetically engineered the mosquitoes to make their brains light up when they were active, and expose them to different types of scent.

Researchers sought to understand the exact blend of components in the air that the mosquitoes used to recognise human odour.

Dr Carolyn “Lindy” McBride spoke on the testing, saying: “We set out to try to understand how these mosquitoes distinguish human and animal odour, both in terms of what it is about human odour that they cue in on and what part of their brain allows them to cue in on those signals.

“We sort of dove into the brain of the mosquito and asked, ‘What can you smell? What lights up your brain? What’s activating your neurons? And how is your brain activated differently when you smell human odour versus animal odour?’”

While human odour is composed of dozens of different compounds, these are also present in most mammals in slightly different ratios.

How were different odours collected?

To compare and test how mosquitoes detected mammal and human odours, scientists collected hair, fur and wool samples and used odour from 16 humans, two rats, two guinea pigs, two quails, one sheep and four dogs.

The Independent wrote: "They then collected human and animal odours nondestructively and designed a system which allowed them to pass human odour at the mosquitoes in the imaging setup.

"This involved creating a wind tunnel to test simple blends or single compounds and breeding viable strains of mosquitoes whose brains responded to the equipment."

In the end the process of the mosquitoes recognising different odour was simpler than the scientists thought, with mosquitoes using just two of their 60 glomeruli (nerve centres) to detect the human odour.

Narrowing down onto the glomeruli that mosquitoes use to detect humans, scientists then identified what these nerve centres were detecting.

They found mosquitoes use these brain centres to detect two chemicals – decanal and undecanal – which have a slightly orangey, citrusy smell and are enriched in human odour.