It is not the mosquito that makes you itch — it is your own body. The mosquito injects a little saliva, and your body answers with an alarm substance called histamine. The histamine makes the red, itchy bump.
Your skin
Mosquito saliva
Histamine — the body's alarm
females only
only the female bites — she needs blood for her eggs
histamine
the substance the body releases, causing itch and swelling
do not scratch
scratching makes more histamine, so it lasts longer