Breakdown: Why do mosquitoes bite & why does it itch?

What happens when a mosquito bites and why is it so itchy?
Published: Sep. 10, 2021 at 11:52 AM CDT|Updated: Sep. 10, 2021 at 11:57 AM CDT
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MEMPHIS, Tenn. (WMC) - Despite all the steps we take to protect ourselves from mosquitoes, they still seem to find their way to us. So, what happens when a mosquito bites and why are they so itchy?

When a mosquito bites you, it doesn’t just help itself to some of your blood — it also kindly gives you some of its spit in return. It’s this saliva that’s responsible for the irritating itch of a mosquito bite, thanks to a concoction of proteins found in it that people are slightly allergic to.

Their saliva contains an anticoagulant (blood thinner) and proteins.

The proteins are foreign substances that trigger the body’s immune system. To fight them the body’s immune system releases histamine, a compound that helps white blood cells get to the affected area. Histamine is what causes the itchiness, inflammation, and swelling.


Only female mosquitoes feed on blood because it’s required for egg development.

The female mosquito will start to feed after landing on a person’s skin. Her mouthparts contain sharp bristles and tubes. The bristles slice a hole in the skin, which allows the female mosquito to probe in the tissue until it strikes a small blood vessel, or capillary. Then two tubes are inserted into the blood vessel or capillary, with saliva flowing through one tube, and the person’s blood being sucked up through the other. The saliva acts as an anticoagulant (blood thinner) that allows blood to flow more easily. The proteins contained in the saliva cause the human immune system to react in the form of uncomfortable itching.

The Anatomy of a Mosquito Bite
The Anatomy of a Mosquito Bite(The Association of Medical Illustrators)


Many people get bitten by mosquitos each year, but bites can affect everyone differently.

Sometimes if a person is bitten for the first time they won’t have a response. This is because their body hasn’t formulated a response to the foreign invader. And some people may not notice bites at all. Others may build up a tolerance over time.

A mosquito bite can last for hours to a few days. The length of a mosquito bite and its symptoms vary depending on the size of the bite and the person’s immune system. Itching or scratching the bite can increase the length of time it lasts.


When you scratch a mosquito bite, this causes the skin to become even more inflamed. Since inflammation causes your skin to itch, you can get into a cycle where scratching will cause even more of an itchy sensation. In addition, by continuing to scratch you run the risk of breaking the skin and causing an infection, leading to even more of an itch.


The Centers for Disease control has remedies and other information here.

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