Why do mosquitos bite some people, but leave others?

Various factors are thought to make one person more attractive to mosquitoes than another. Photograph: Shutterstock

It’s a situation many of us have been faced while on holiday with a partner or a friend.

One will become absolutely covered in mosquito bites, whilst the other escapes almost completely unscathed. 

And while the red, sore, bumpy bites are bad enough the buzzing assailants can also spread a host of dangerous pathogens, and are an increasing health risk in Europe

So, what makes one person more attractive to the vampiric bloodsuckers than another?

Here MailOnline explains what experts say is, and isn’t, the key behind the phenomenon.

How big you are and how you breathe

Mosquitoes track down their prey by scent and one the things they are on the hunt for is carbon dioxide.

Carbon dioxide (CO2) is a gas that we exhale as we breathe, and acts as a homing beacon to the insects.

However, quantity of CO2 does seem to matter. Larger people naturally exhale larger quantities of carbon dioxide and it’s for this reason experts say they tend to get bitten more.

In the real world this translates to men getting bitten more than women, pregnant women getting munched more than non-pregnant women, and adults being plagued by bites more than children. 

Dr Robert Jones, an expert in disease control from the London School of Hygiene & Tropical Medicine, said fatter people may also be targets for this reason. 

‘Amongst a group of people, the proportion of bites upon an individual has been associated with the proportion of the total surface area or weight contributed by that individual to the group,’ he said. 

The same logic is thought to apply to people with an increased rate of breathing like those doing exercise.  

Your natural scent as well as the bacteria on your body

People’s unique aroma is also believed to play a role in mosquito victim selection.

Our natural scent is determined by a combination of our genetics as well as the skin’s microbiota, the community of microscopic organisms that live on the surface of our flesh.

Tests, where people wear nylon strips to extract their musk which are then hung in front of swarms of mosquitoes, have clearly shown the insects do have a preference when it comes to particular aromas. 

Similar studies on twins have suggested genetics could account for as much as 67 per cent in mosquito attraction. 

While evidence that personal aroma accounts for a significant part of mosquito attraction, scientists are still trying to unpick exactly what compounds we waft into the air are responsible and what we can do to mask or reduce them. 

Dr Jones said: ‘We believe that genetic factors and our skin microbiome affect the volatile compounds that our bodies produce, and this in turn affects how we smell.’

Mosquitoes track down their prey by scent and one the things they are on the hunt for is the carbon dioxide people exhale as they breathe.

‘Some of these compounds have been shown to be attractive to mosquitoes, so if your body produces lots of these compounds you may attract more mosquitoes than other people. 

‘We are interested in ways that these compounds could be masked or their relative abundances could be altered to make people less attractive.’

Choosing your outfit could make you a target

Whilst smell is a mosquito’s best sense it’s not the only one with studies showing the insects prefer some colours over others. 

Experiments have shown they have an overall preference for red, orange, black or cyan.

In contrast, green, blue or purple colours didn’t attract the bloodsuckers’ attention. 

Experts believe mosquitoes have evolved this sense to distinguish between prey and the ambient environment once they’ve sniffed them out. 

Mosquito vision isn’t the same as human eyesight and all human skin regardless of pigmentation will appear red/orange to the bugs. 

Experts said people might be able to reduce the chance of mosquitoes biting them by avoiding wearing the colours they find attractive.

Does your blood type really make you more delicious? 

One of the more common beliefs is that your blood type, specifically type O, makes you a more desirable meal to mosquitoes. 

However, whilst some studies have found this is the case, other tests have been inconclusive. 

Dr Jones said, overall, blood type is probably not an important component of mosquito attraction.

‘There does not seem to be strong evidence for blood types affecting how attractive people are to mosquitoes. Other factors are more important,’ he said.  

What about what you eat or drink? 

Numerous food and drink are purported online to either attract or repel mosquitoes.

Some, like garlic, are touted under the logic that the strong smell will help mask your own scent, acting as a type of olfactory camouflage.

On the opposite side salty or sweet foods are claimed to have the opposite effect producing compounds that makes us more attractive to mosquitoes.

One study, admittedly only on 14 people, found mosquitos were more likely to land on a person after they’d had a some beer.

Even beer might not be a safe option. One study, admittedly only on 14 people, found mosquitos were more likely to land on a person after they’d had a drink.   

But actual evidence that these work is mixed. Multiple studies have either failed to show what we eat or drink influences mosquitoes or are very limited in their findings.

Dr Jones said, given the unreliable nature of using food or drink to ward off mosquitoes, people are better off sticking to standard repellents.  

‘It is much better to use methods that have been proven through rigorous scientific tests to provide a high level of protection from bites,’ he said.

‘There are several insect repellent compounds that are effective for many hours against a range of mosquito species and can be safely used by both adults and children.’

It might, just a little bit, be all in your head

Another factor to consider in the mosquito preference debate is that it might be you that’s the problem.

Dr Jones explained that some people have worse reactions to mosquito bites than others.

This can make their bites seem worse by itchier, larger and sorer so even can make it seem like they’ve been chomped on more than another person with the same number of nibbles.  

So, what can I do to try and avoid becoming a mosquito buffet? 

Tips for avoiding mosquito bites include wearing long sleeved clothing and trousers, using insect repellent, keeping accommodation windows closed or using fly screens, and sleeping under a mosquito net.

People should be especially cautious during the early morning and early evening as these are when mosquitoes are most active.