Your turn
Each lab is one step from the video. Change things and see what happens.
Each lab isolates one part of the story. The models are simplified to show the idea; they are not medical tools.
Tap the buttons and see what happens.
Tap a mosquito. Where does it fly: to the flower, or to the blood?
Tap each mosquito. Bushy (plumose) antennae mark males, which only feed on nectar.
Tap a mosquito. Fluffy feelers? That's a daddy!
Drag the person around, or switch the breathing off. What does she follow?
Drag the host and toggle exhaled CO₂. Breath works at long range, odour mid-range, heat at landing.
Drag the child. Can the mosquito still find them?
A simplified model: real cue ranges depend on wind, the species and the person.
Step through the bite one blade at a time. Which tube sips, and which one spits?
Step through: labium buckles, maxillae saw, labrum probes, hypopharynx injects saliva.
Tap Next step and watch the tiny needles go in.
Squirt in saliva, then try the antihistamine and the scratch. What happens to the itch?
Add saliva antigen, then block histamine or scratch. Watch the wheal and the nerve signal.
Squirt in spit. Then try the cream, and try a scratch.
A simplified model: histamine is only part of the itch story.
Change each friend's skin acids, breath and heat. Who attracts the swarm?
Adjust skin carboxylic acids, CO₂ and heat. Swapping blood types makes no clear difference.
A toy model: the weights are made up to show the idea from the 2022 study.
A mosquito bite itches because of you! When a mosquito bites, she leaves a tiny bit of spit in your skin. Your body notices the spit and makes the itch.
Daddy mosquitoes drink sweet juice from flowers. Mommy mosquitoes drink it too, but they need a little blood to make their eggs.
She smells the air you breathe out. Then she smells your skin. Then she feels how warm you are, and lands.
Her mouth looks like one needle, but inside are six tiny ones. Two little saws cut in gently. A bendy straw finds blood, and a tiny tube squirts in spit to keep the blood flowing.
Your body says, "Who are you?" Little guard cells let out a special juice. The juice makes a bump and tickles your nerves. That tickle feels itchy!
This page explains how the body works; it isn't medical advice.
A mosquito bite itches because of your own immune system, not because of the tiny hole. While she drinks, a female mosquito leaves some of her saliva in your skin.1 Your body doesn't recognise the proteins in that saliva, so it treats them as invaders. Immune cells in the skin called mast cells release a chemical called histamine. Histamine makes tiny blood vessels leak fluid, which swells the spot into a bump, and it stimulates nerve endings, which your brain feels as an itch.56
In other words, every mosquito bite is a small, local allergic reaction.5 Scientists agree that histamine is a big part of the story, though the exact details are still being studied, and other chemicals can add to the itch too.6
Only female mosquitoes bite. Males don't bite people or animals at all.1 Both males and females drink sugary flower nectar and plant juices for energy.414 But a female needs extra protein (and iron) to build her eggs, and most female mosquitoes can't produce eggs without a meal of blood.15 So every mosquito that bites you is a mother-to-be collecting food for her eggs.
There are more than 3,500 kinds of mosquito, found on every continent except Antarctica. The ones that bite people most belong to three groups: Aedes, Culex and Anopheles.6
A hungry female follows a trail of clues, in roughly this order:126
| Clue | What it tells her | Range |
|---|---|---|
| Carbon dioxide in your breath | A breathing animal is nearby | Up to almost 30 feet (about 9 m) |
| Skin odour (sweat + skin bacteria) | That animal is a human | Closer in |
| Body heat (and moisture) | A warm spot to land on | Very close |
Carbon dioxide and heat just say "warm-blooded animal here". Skin odour is what tells a mosquito like Aedes aegypti that the animal is a person.7 Mosquitoes also look for dark shapes as they get close.6
A mosquito's long mouth, the proboscis, looks like a single needle, but it's really a sheath (the labium) wrapped around a bundle of six thin blades called stylets.9 Here's what each part does:
That saliva is the important bit. It's the part of the mosquito that stays behind, and it's what your body reacts to.113
Once the saliva is in your skin, your immune system gets to work:
Mosquito saliva itself contains a little histamine too, and there's good evidence for the histamine idea: antihistamine medicines make the bumps smaller and less itchy.6
The bump is fluid that leaked out of tiny blood vessels because of histamine.6 Most people get a puffy, reddish bump a few minutes after the bite.1 It's usually 2–10 mm across and biggest after 20–30 minutes. Some people also get a second, delayed itchy bump that peaks 24–36 hours later, and then fades over several days.6
People react differently. Some barely notice a bite; others get a large swollen area. Big reactions (sometimes called "skeeter syndrome") are more common in children.13 Reactions can also change over a lifetime: many people who are bitten a lot become less reactive over the years, though this varies a lot from person to person.613
You're not imagining it. Some people really are "mosquito magnets", and skin odour seems to be the biggest reason.
What about blood type? You may have heard that mosquitoes prefer type O blood. The studies on this are contradictory, so it's not a reliable explanation.7
Most bites go away on their own in a few days.3 To feel better in the meantime, the CDC suggests:1
Try not to scratch. Scratching can break the skin and let germs in, and it can make the itch worse by prompting even more histamine.145 Tell an adult or see a doctor if a bite looks infected (red, warm, or with a red streak spreading from it), or if you get a fever, bad headache or body aches.13
For most people, a mosquito bite is just an itchy nuisance. But in some parts of the world, mosquitoes can carry germs that cause illnesses such as malaria, dengue, Zika and West Nile virus.13 That's why health agencies recommend preventing bites: use an EPA-registered insect repellent (such as DEET or picaridin) as the label says, wear loose long sleeves and long pants, and keep window screens in good repair.123
When a mosquito bites, she leaves a little saliva in your skin. Your immune system treats the saliva proteins as invaders, and mast cells release histamine. Histamine makes the spot swell and stimulates nerve endings, which your brain feels as an itch.
Only female mosquitoes bite. They need the protein in blood to make eggs, and most can't lay eggs without a blood meal. Male mosquitoes don't bite; they drink flower nectar.
Mosquitoes follow carbon dioxide from your breath from far away, then skin odour, then body heat close up. A 2022 study in the journal Cell found that the people who attract the most mosquitoes have more carboxylic acids on their skin (skin bacteria help make them), and this stayed the same over several years.
The evidence is mixed. One study found more mosquitoes landed on people with type O blood than type A, but other studies disagree. Skin odour, breath and heat are better-supported explanations.
Scratching irritates the skin, and nerves in the skin can prompt mast cells to release even more histamine, which makes a vicious cycle. Scratching can also break the skin and let germs in, so it's best to avoid it.
A puffy bump usually appears within minutes and is biggest after 20 to 30 minutes. Some people also get a delayed itchy bump that peaks a day or so later. Most bites fade within a few days.
Wash the bite with soap and water, hold an ice pack (wrapped in a cloth) on it for about 10 minutes, and ask a grown-up about an over-the-counter anti-itch or antihistamine cream, following the label. Try not to scratch: it makes the itch worse and broken skin can get infected. Tell a grown-up or see a doctor if the redness spreads or you get a fever, bad headache or body aches.
Ask a grown-up to put on an EPA-registered insect repellent (adults spray it on their own hands, then rub it on a child's skin), wear loose long sleeves and long pants, and once a week tip out anything outdoors that holds water, like buckets, plant saucers and old tyres, because mosquitoes lay their eggs in standing water.