Why Do Mosquito Bites Itch?

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Mosquito bites are an annoying part of life because they itch and swell and bother us for days at a time. In this lesson you'll learn why mosquito bites itch, though the answer to this question might surprise you!

Mosquitoes are a Pain!

I don't know about you, but one thing that drives me crazy is an itchy mosquito bite. The buzzing around your ear is bad enough, but when they land on you and take a bite, it leaves an effect that can last for days. But why do those bites itch so much? And why are mosquitoes biting you in the first place?

Female mosquitoes use components in our blood for egg production.
mosquito biting

You may be surprised to learn that only female mosquitoes bite. That's right-- males don't care about us at all. And what's even more interesting is that a female mosquito doesn't bite us for her own benefit, but instead uses our blood proteins and other components for egg production. She does this by sticking her proboscis, which is an elongated tube-like mouth part, into our skin and finding a juicy capillary from which to get blood.

Now, your body has a natural defense mechanism from even small harms like this. Normally when you get cut or injured your blood will coagulate or turn to solid. This prevents your body from losing blood in the event of an injury. Unfortunately, the female mosquito has developed her own defense against our body's defense, and that is an anticoagulant in her saliva. This anticoagulant keeps the blood flowing so that she can get her fill out of you. Pretty tricky!

An Itchy Intruder

But here's where it gets really interesting, because not only does that saliva keep our blood flowing but it also causes that annoying itch and that lovely bump called a wheal. These reactions occurs from an allergic reaction to the saliva itself. Our bodies respond to the presence of this allergen, or substance that causes an allergic reaction, by producing histamine. This sends blood and white blood cells to the bite and causes that itching, swelling, and inflammation, all of which are designed to protect you from this bodily intruder.

A wheal is the bump on your skin that occurs from a mosquito bite.
mosquito wheal

This would be a fantastic response if mosquito saliva was dangerous to our health. But much like dust, cat dander, pollen, and other allergens, mosquito saliva is harmless. So instead of saving our lives, in this case histamine mostly just causes us frustration and discomfort.

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