The body has two types of immunity-innate immunity, and acquired immunity. Inet immunity is useful in mosquito bites.
Mast cells are a type of cell and immunoglobulin E (IgE) is responsible for redness and itching after a mosquito bite. When a mosquito bites for the first time in human life, there is no problem. But the toxins secreted by the mosquito penetrate the skin and irritate the immune system. Immunity targets it as a harmful thing and builds the body so that it can be removed quickly the next time it is noticed. IgE recognizes this toxin. This is called sensitization.
The next time a mosquito bites a toxin, the sleeping IgE wakes up and pushes the mast cell. Mast cells release a number of chemicals, the most important of which is histamine.
This histamine causes the capillaries to swell (dilation of capillaries) where the mosquito bites, and irritates the nerves there. This results in red swelling (swelling of the blood vessels) and itching (for irritated nerves). It is good for our body, even if it is difficult, because too much blood quickly dilutes the toxin and removes it, and the itching attracts white blood cells (WBCs) and clears the area. After that both itching and redness decrease and the skin becomes normal again. Simply put, it is because of histamine.