How & Why Do Mosquitoes Leave Itchy, Red Bumps on Your Skin?

As soon as a mosquito lands on you, she starts probing with her proboscis, or stinger, for a place that allows her to take the most blood in the fastest time. The tip of her proboscis is very flexible, bending enough to allow her to poke around a fairly large area without having to pull it out and plunge it back in again to search for another spot. Her stinger contains two tubes. One sends her saliva, which contains a substance that prevents blood from clotting, down into your skin. With the other, she sucks blood up into her body. It takes the mosquito about four minutes to drink her fill.

Histamines, which are produced by your immune system, are the human body's bodyguards. These chemicals are released whenever something that shouldn't be inside your body tries to sneak in. Since humans are allergic to mosquito spit, your immune system immediately sends histamines rushing to the spot to fight off the poison and prevent it from traveling anywhere else via the bloodstream. This battle between histamines and mosquito saliva makes the blood vessels in the area swell up, creating a red bump. The nerves around the mosquito bite also become irritated, which your body perceives as itching.

The carbon dioxide we exhale in our breath is the first thing that advertises our presence to mosquitoes. These bloodhounds of the insect world can smell carbon dioxide from as far as 164 feet away, so after they catch a whiff, all they have to do is follow it to its source. The larger people are, the more carbon dioxide they exhale, which is why adults tend to get more mosquito bites than kids. As the skeeters draw closer, they can also pick up differences in body heat between individuals, and smell chemicals plentiful in sweat, including lactic acid, uric acid and ammonia. During and after exercise, people exhale more carbon dioxide, and sweat more, than people at rest.

Mosquitoes really do prefer biting some people more than others. Scientists don't fully understand all the reasons why, but they do know that the bugs prefer type O blood to any other. They are also partial to a few kinds of bacteria, so people who have more of these on their skin will entice mosquitoes. The tiny vampires also seem to love beer drinkers. Pregnant women, who have slightly higher body temperatures and exhale more carbon dioxide, get twice as many bites as others. Mosquitoes also use their vision to hunt, so the color of your clothing is a factor. Black, red and dark blue are their favorites.