Mosquito magnets

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Genetics / Health / Medicine / Myths / Zoology

Are you irresistible to mosquitos? We all know someone who gets covered in bites every time they venture outside. Why are some of us so much tastier than others?

Are you irresistible to mozzies? Image credit Erik F Brandsborg via Flickr

The deadliest animals

Only female mosquitos bite: they need the protein that comes from a blood meal to make their eggs. But there are thousands of species of mosquito, and they have different ideas about who and what is tasty. Some prefer birds, some frogs, some reptiles and some choose to bite mammals. And as we know only too well, some are particularly fond of humans.

Mosquitos are attracted to body heat and carbon dioxide, which we breathe out. That makes good sense: warmth and carbon dioxide are reliable signs that a body contains blood. So anything that increases your body temperature or makes you release more carbon dioxide will make you more of a target. This includes having a bigger body, being pregnant, or exercising.

But once a mosquito gets a bit closer there are a variety of factors that make you more or less appealing. The bacteria and chemicals we carry on our skin and that we release in sweat play a big role. In one study, researchers identified 300 different chemical compounds on skin that may play a role in attracting or repelling mosquitos.

Given mosquitos are responsible for the spread of some serious diseases – like malaria, yellow fever, dengue, Zika and Ross River fever – there has been a lot of research into what attracts them. After all, mosquitos are famous for being the ‘deadliest animals’.

Beer and genes

First of all, there’s no good evidence that anything you eat or drink changes how attractive you are to mosquitos. Taking Vitamin B tablets will not keep mosquitos away. Nor will eating garlic. But one small study did suggest drinking beer may make you more appealing to mosquitos.

One of my favourite studies of mosquito preferences compared mozzies’ responses to human hands, socks that had been worn for three days and Limburger cheese – that’s the REALLY smelly one. Human hands got the most interest from the mosquitos.

But the smelly socks were a big drawcard too – we know mosquitos respond to our sweat. Lactic acid attracts mosquitos – another reason why exercising is likely to make you more of a target. There’s also evidence some species of mosquito are attracted to people who have O-type blood.

And research published a couple of years ago showed our genes also play a role in our mosquito magnetism. The study showed identical twins were equally attractive to mosquitos, but non-identical twins weren’t. There’s a lot more work to be done on understanding the role of genetics in how mozzies respond to us.

Mozzies, be gone

If mosquitos happen like you a lot, what are your options? A study published earlier this year set up a wind tunnel in a lab designed to replicate a backyard patio. One unlucky person acted as bait at one end of the tunnel while the scientists counted how many yellow fever mosquitos moved towards the bait.

The researchers tested a variety of repellents on the human bait: sprays, wearable devices and a citronella candle. Most of them only had a weak effect, or no repellent effect. Neither bracelets containing herbal extracts or sonic mosquito repellers worked at all. Citronella candles were no good either: in fact, they might slightly attract mosquitos. But DEET and the oil of lemon eucalyptus both reduced mosquito attraction by 60%. Another study showed that while mosquito coils may reduce the number of mosquito bites, they don’t stop people getting malaria.

Australia’s mozzie expert Dr Cameron Webb has explained there are a variety of ways to avoid having your Christmas barbeque spoiled by mosquitos. For example, get rid of any places in your garden they could breed – bird baths, and other water-filled containers. Wear loose clothing and apply mosquito-repellents properly.

And the other thing to remember is that you may not be getting bitten more than your friends, you may just have more of a reaction to bites. Mosquitos inject saliva when they bite and you may react to that saliva more than others.

So if you’ve got a friend who is bragging about how they never get bitten, let them know they may very well be wrong. Something that could really matter when it comes to travelling in places where the mozzies carry nasty diseases.

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