Why does a bag swell up in the place where a mosquito has bitten?

After a mosquito bite, the toxins secreted in the mosquito's mouthparts will remain in the mosquito bite in the human body, and then the body's immune system will work, and a large number of white blood cells will begin to gather in the mosquito bite to destroy the toxin, so the part will quickly swell.

Almost everyone has the unpleasant experience of being "bitten" by mosquitoes, in fact, it should be said that they have been "stung" by mosquitoes. Mosquitoes can't open their mouths, so they won't bite on the **, it actually uses 6 needle-like structures to pierce people**, these short needles are the center of the mosquito's edible mouthparts.

These short needles suck human blood in the same way that they draw blood; The mosquito also releases saliva containing anticoagulants to prevent blood from clotting, so that it can feast peacefully. When the mosquitoes are full of food and drink and float away, all they leave behind is an itchy lump.

However, the itchy sensation is not caused by a short needle pricking or chemicals in the saliva. We feel itchy because the body's immune system releases a protein called histamine to fight foreign substances, and this immune response triggers an allergic reaction at the bite site. Histamine causes swelling of the tissues around the bite when blood flows to the bite site to speed up tissue recovery, and the intensity of this allergic reaction varies from person to person, with some people having a more severe allergic reaction to a mosquito bite.

Only female mosquitoes bite mammals because they have to suck blood every three or four days to get the protein they need to make eggs; Male mosquitoes mainly feed on nectar, while female mosquitoes use animal body heat and physiological changes to search for targets, which may be why human ankles and feet are more commonly bitten by mosquitoes, because the blood vessels in these parts are closer to the body surface, so more body heat is released.

To put it simply: it is an allergic reaction of the human body to the substances left behind by mosquitoes after sucking blood.

Detailed explanation:

When mosquitoes bite people, they inject several proteins into the human body, collectively known as mosquito saliva proteins. These proteins inhibit the body's blood clotting system, preventing blood clotting and preventing blood vessels from constricting so that mosquitoes can smoothly suck up the blood. After sucking the blood, the mosquito flew away, but the mosquito saliva protein remained in the human body.

The body's immune system is mobilized to try to remove these foreign substances, and an immune response occurs. In this process, a substance called histamine is released, which causes capillaries to dilate, increasing the permeability of the walls of blood vessels, filling cells with fluid, and inflammation occurs. At this time, the mosquito bite area is itchy, red and swollen.

If the mosquito does not carry the pathogen, the little blood sucked by the mosquito is negligible to the human. What is uncomfortable is the itching at the bite site, which is caused by the body's immune system unnecessarily acting against mosquito saliva proteins, which is actually an allergic reaction. There are three types of allergic reactions caused by mosquito bites, some reactions are very fast, appearing after a few seconds of being bitten, but they disappear quickly, and they disappear after a day; Some reactions appear a day later and last for days or even many days before disappearing.

Blood group problems. In particular, the more you scratch it, the more serious it becomes. The more you scratch, the more itchy it gets, the more you scratch it, the bigger the bag. It's best not to hold back, and it'll be fine soon. Do a good job of mosquito prevention facilities, remember to rub some toilet water, wind oil essence, soapy water, toothpaste or something when you are bitten.