Why do mosquito bites itch?

It's not the bite that itches—it's your body's reaction to it
Aedes Mosquito
Aedes mosquitos that can transmit the Zika virus are native in some parts of the United States, but not widespread throughout the country. CDC

Why do mosquito bites itch?

The bite doesn’t cause the itch—your body does. When a female mosquito bites you (only female mosquitoes bite), she injects a small amount of salvia first.

Her spit is an anticoagulant—it stops your blood from clotting and trapping her while she feasts.

Your immune system recognizes the spit as foreign and creates histamines to attack it. The histamines make your blood vessels swell. This causes an itchy wheal, aka the bump from a bite.

Try not to scratch it!