Mosquito bites create a break in the skin which in turn activates our immune system to protect us. The mosquito’s saliva is recognised as an unknown substance which needs to be flushed out. The swelling around the bite is caused by histamine, which is produced by the immune system. The result is a swelling around the mosquito bite due to increase in white blood cells. We feel the itch as the histamine sends a signal to the nerves around the bitten area.