Why Does A Mosquito Bite Swell And Itch?

A quiet walk outside, or a roof top dinner or a long planned hike turns regretful once a mosquito lays its eye…or should I say its mouth on you! An after effect of a mosquito bite is one of the most irritating and annoying sensation we go through every day. After a mosquito bite, you’re left scratching and soothing your skin while all the time it swells up around it. So what causes this swelling and itching?

Why Do Mosquitoes Bite?

Only female mosquitoes bite. They do so in order to produce eggs of their own. Blood is rich in nutrients that are essential for egg production. This drives their frenzy!

The male mosquitoes do not bite. Instead, they get their nutrition from feeding on plant nectar and alike that they can find in their habitat. The female mosquitoes also feed on the same. In short, males are vegans and females are non-vegans!


How Does A Mosquito Bite?

For a mosquito to bite, it has to find you. Yes, it can see you, but it can also be drawn to you if:

  • You generally have a warm body temperature
  • Contrasting coloured clothing
  • You have a particular body odor (due to presence of Lactic acid and CO₂) that mosquitoes take after.

Once a mosquito lands on the skin surface, it starts searching for blood vessels from which it can draw blood. A mosquito may take several attempts to find a blood vessel. Research shows that half the mosquitoes fail in finding a blood vessel!

On finding a juicy blood vessel, it inserts the tip of its mouth into the vessel. The long needle like structure that the mosquito uses to poke and draw blood is called proboscis.

What Happens During The Bite?


By Prof. Frank Hadley Collins

After successfully inserting its proboscis into the blood vessels, it starts to draw blood from it. Simultaneously, it injects its saliva into the vessel via another tube. Its saliva contains certain proteins that keep the blood from clotting, so that the blood doesn’t clog. The proteins prevent the blood from clotting and inhibit platelet aggregation so that a free flow of blood is maintained to suck. It also has vasodilatory substances that keep the blood vessel wide and not constricted!

Swelling, Redness and Itching


By ProjectManhattan/ CC BY-SA 3.0

After the proteins from the mosquitoes are released into the blood, our immune system reacts to it. The body releases chemicals called histamines at the bite site. The histamines causes the blood vessels at that site to swell up to allow white blood cells and other proteins to offend the invading foreign object. This swelling of the blood vessels produces the redness and itchiness. The histamines are responsible for the redness, itching and swelling…not the mosquito!

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