Every summer barbecue seems to have one: the person slapping their ankles all night while everyone else barely notices a mozzie. So why do mosquitoes bite some people more than others? Forget the old line about “sweet blood”. The strongest evidence points to something you can’t easily change: the natural smell of your skin. But there’s a second part to the answer that many articles skip, and it might explain why you think you’re bitten more than you actually are.
Bitten more, or just itchier?
Before blaming your blood, it’s worth separating two different things: how often you’re bitten, and how badly you react. Only female mosquitoes bite, because they need the protein in blood to make eggs. When one bites, she injects a little saliva into your skin. It’s your immune system’s reaction to the proteins in that saliva that causes the red, itchy lump, not the bite itself.
People react very differently. Medical entomologist Cameron Webb of the University of Sydney explains that a few people suffer strong allergic reactions, sometimes called “skeeter syndrome”. He also notes that young children usually react worse than adults, because we tend to become more tolerant as we get older, as he wrote in a piece republished by NSW Health Pathology.
Your reactions can change over time, too. People bitten by an unfamiliar species, for example after moving or travelling, may react differently, because saliva varies between species, according to Gavi. So the friend who swears mosquitoes never touch them may simply be bitten and barely notice, while you come up in welts. That said, the research shows that some people genuinely are bitten far more than others.
How a mosquito finds you
A hungry mosquito tracks you down using several senses at once, roughly in stages. From a distance, the first clue is carbon dioxide, the gas you breathe out. Mosquitoes can detect it from as far as 100 feet, about 30 metres, away, according to Smithsonian Magazine, and it tells them a warm-blooded animal is nearby.
As they get closer, they start using sight, then the smell of your skin, and finally your body heat and moisture when they’re almost on you. That’s why it’s so hard to hide from them: block one cue and they switch to another.
The main reason: how your skin smells
The strongest evidence comes from a 2022 study at Rockefeller University in New York, published in the journal Cell. Neuroscientist Leslie Vosshall and her colleague Maria Elena De Obaldia asked volunteers to wear nylon stockings on their forearms for six hours at a time, so the fabric soaked up their natural skin scent. The team then pitted pieces of the stockings against each other in a chamber of Aedes aegypti mosquitoes, the species that spreads dengue and Zika, in a kind of knockout tournament.
The results were striking. According to Rockefeller University’s release on ScienceDaily, the biggest mosquito magnet was about 100 times more attractive than the least attractive volunteer. The published paper found that the most attractive people produced significantly more chemicals called carboxylic acids on their skin.
These acids are part of sebum, the oily layer that keeps skin moisturised. The bacteria living on our skin break them down, which produces part of the smell that makes us recognisably human to a mosquito.
The researchers kept testing some volunteers for several years, and the magnets stayed magnets. As De Obaldia put it, people who were mosquito magnets in the study remained mosquito magnets. That suggests being a magnet is largely built in, probably shaped by your genes and the particular mix of bacteria on your skin.
There’s a caveat worth knowing, though. The NIH’s summary of the research points out that the study showed these acids were associated with attractiveness, not that they directly cause it. One volunteer with high levels of every acid tested didn’t attract mosquitoes at all.
What else makes you a target?
Skin smell is the main factor, but other things can make you more of a target. Because carbon dioxide is the first clue a mosquito follows, anyone who breathes out more of it stands out more. That includes larger people, people who have just been exercising, and pregnant women. Smithsonian Magazine reports that pregnant women breathe out about 21% more carbon dioxide and run slightly warmer around the belly. Heat and sweat matter at close range too, which is partly why you seem to attract more mozzies after a run, a game of touch footy or an afternoon in the garden.
Your skin bacteria play a part as well. A 2011 study found that people with large amounts of certain kinds of skin bacteria were more appealing to mosquitoes, Smithsonian notes. That fits with the 2022 finding that bacteria breaking down skin acids help create the smell that draws mosquitoes in.
And then there’s beer. A 2010 study in PLOS ONE found that drinking a litre of beer made people more attractive to malaria mosquitoes. The researchers checked whether it changed people’s breath or body temperature and found it didn’t, so nobody yet knows why.
Does the colour of your clothes matter?
It can, because mosquitoes use their eyes as well as their sense of smell. A 2022 University of Washington study, published in Nature Communications, found that once Aedes aegypti mosquitoes detect carbon dioxide, they fly towards certain colours. They favour red, orange, black and cyan, and mostly ignore green, blue, purple and white.
Human skin of every tone gives off a strong red-orange signal to a mosquito’s eyes, which may help explain the preference. So on a summer evening outdoors, a light-coloured, long-sleeved shirt is a better bet than a black or red one.
Does blood type make you a mosquito magnet?
Probably not, or at least not by much. A few small studies have suggested mosquitoes prefer people with type O blood, but the results have been inconsistent and the evidence is weak. Mosquitoes can’t test your blood before they land, so any effect would have to come through something else, such as skin chemistry.
Vosshall says the same is true of most other popular explanations, including blood sugar, eating garlic or bananas, being a woman or being a child: there’s little credible data behind any of them. And despite what you may hear at the pub, there’s no good evidence that eating garlic or taking vitamin B tablets keeps mosquitoes away. A proper repellent does.
Mosquitoes in Australia: more than an itch
For most of us, a mosquito bite is just an itchy annoyance, and most mosquitoes in Australia don’t carry disease, according to the National Health and Medical Research Council’s (NHMRC) mosquito-borne diseases fact sheet. But some do, which is why it pays to avoid bites, especially in summer and after heavy rain or flooding.
The most commonly reported is Ross River virus, which can cause joint pain, swelling and fatigue that can drag on for months. Barmah Forest virus is also common, dengue occurs in northern Queensland and the Torres Strait, and malaria is usually caught overseas. Much rarer but potentially very serious are Japanese encephalitis, Murray Valley encephalitis and Kunjin virus, which can affect the brain. Healthdirect has more on the symptoms of each.
There’s a vaccine for Japanese encephalitis, free for some people at higher risk. For the other mosquito-borne diseases found here there’s no vaccine, and the Australian Centre for Disease Control notes there’s no specific treatment for Japanese encephalitis either. So not getting bitten is your best protection.
One more thing worth knowing if you live in or visit the tropical north: Aedes aegypti, the mosquito that spreads dengue, bites mainly during the day, with peaks in the early morning and late afternoon. The usual advice about dawn and dusk isn’t enough on its own there.
How to avoid getting bitten
If you’re a mosquito magnet, you can’t change your skin chemistry, but you can make yourself much harder to bite. To avoid bites, Australian health authorities recommend:
- Use an effective repellent. ACT Health says the most effective contain diethyltoluamide (DEET), picaridin, or para-menthane-3,8-diol (PMD), also known as oil of lemon eucalyptus. Put it on all exposed skin, follow the label, and reapply after swimming or a lot of sweating. If you’re also wearing sunscreen, put the sunscreen on first.
- Don’t let young children apply their own repellent. For babies under 12 months, repellents generally aren’t recommended, so rely on nets and clothing, and check the label and your state’s advice for older children.
- Cover up with loose, light-coloured, long-sleeved shirts and long pants, especially in the evening.
- Take extra care at dawn and dusk, when many mosquitoes are most active, and during the day in the tropical north.
- Get rid of standing water around the house, where mosquitoes breed. Tip out plant saucers, buckets and kids’ pools, clean pet water bowls and keep gutters clear, as the Australian Centre for Disease Control recommends.
- Keep screens in good repair, including flyscreens and tent mesh, and use a mosquito net when camping in mosquito country.
If you do get bitten
Try not to scratch, because it makes the inflammation worse and can break the skin and let infection in. Cameron Webb suggests a cold pack to calm the swelling, and an anti-itch cream from the pharmacy can help. If you react badly every time, a pharmacist can recommend an antihistamine.
See your GP if a bite becomes very swollen, hot or painful, which can be a sign of infection. See them too if you feel unwell after being bitten, particularly with fever, headache, joint pain or a rash, and mention where you’ve been.
Once a mosquito magnet, always a mosquito magnet
So if you’re the one who gets eaten alive at every barbecue, it’s not your imagination and it’s not your “sweet blood”. The biggest reason is the natural smell of your skin, shaped by its oils and the bacteria living on it, and it seems to stay with you for years. Breathing harder, being hot and sweaty, a few beers and dark or red clothing can all make it worse. If you also happen to react strongly to bites, it will feel worse still. You can’t swap your skin, but a decent repellent, light-coloured long sleeves and a bit of planning around dawn and dusk work just as well for mosquito magnets as for everyone else.
A quick note on health: I’m not a doctor, and this is a general explainer, not advice for your situation. If you feel unwell after mosquito bites, particularly with fever, headache, joint pain or a rash, see your GP or call Healthdirect on 1800 022 222. In an emergency, call 000.
If you’re battling other biters around the house, my post on bed bugs covers another unwelcome one.
Sources
- ScienceDaily (Rockefeller University): Why some people are mosquito magnets (2022)
- Cell (via PubMed Central): Differential mosquito attraction to humans is associated with skin-derived carboxylic acid levels
- NIH Research Matters: Skin compounds associated with attractiveness to mosquitoes
- Smithsonian Magazine: Why do mosquitoes bite some people more than others?
- PLOS ONE: Beer consumption increases human attractiveness to malaria mosquitoes (2010)
- University of Washington: Mosquitoes are seeing red (2022)
- NSW Health Pathology (Cameron Webb): What causes the itch in mozzie bites?
- Gavi: Why do some people react so badly to mosquito bites?
- NHMRC: Mosquito-borne diseases fact sheet (PDF)
- Healthdirect: Mosquito-borne diseases
- Australian Centre for Disease Control: Reduce your risk of mosquito-borne illness
- ACT Government: Mosquitoes