why do mosquito bites itch?

Source: World Health Organization (WHO)

             When a mosquito bites you, she not only takes some blood, but she leaves behind her saliva. The saliva has a blood thinner that keeps your blood from clotting. In other words, the mosquito can quickly draw blood without catching your attention. But, her saliva also mixes with your blood and, in response, your body produces histamines that cause inflammation and itching. Your skin around the bite area gets itchy.

             Usually, over-the-counter oral antihistamine medications or topical antihistamine creams can help once you get a bite. But, if you do not get well in the next 3 to 5 days, then go see a doctor. Some mosquito bites may cause severe health conditions.

             Since mosquito bites can cause more than an itch, it is a good idea to avoid them when you can. Mosquitoes are most active during the hours just before and after sunrise and sundown. It can help to wear protective clothing, although some mosquitoes can drill right through clothing. Use insect repellent if you are in areas with large mosquito populations. Also screening windows and keeping doors shut can keep mosquitoes out of your home.