Here’s a vexing question asked at summer camp, either by the junior mountaineers, and kids everywhere. Why do bug bites itch? The answer is, they DON’T! Bug bites don’t itch at all. Sometimes you don't even feel them. It's pretty amazing because what goes on under your skin when a bug bites you is horrifying.
Alright, some insects like certain kinds ants are venomous. So, their bites can itch because their venom contains formic acid. This can irritate impulse to the skin.
Let’s talk about nematocera, the suborder insects that includes black flies and mosquitoes. These bugs have a long bendable proboscis that they stick into you to drink your blood. The proboscis is made up of 6 different mouthparts.
First is the mandibles which are hooked and the two maxillae which are separated like steak knives. These part go as deep as they can to make an opening for the other two mouth parts to pass through---the labrum and the hypopharynx. Those are both long hollow flexible tubes and they wriggle around inside you like a worm while the bug probes around for blood vessels.
Once it finds one, blood gets sucked up through the labrum and saliva is injected down through the hypopharynx. That saliva is an anti-coagulant; it stops your blood from clotting inside the bug’s proboscis so that it can keep drinking.
It’s also the main factor for diseases that are transmitted by mosquitoes like malaria and West Nile virus.
It has one other awesome property; you are probably allergic to it. When you're allergic to something your body produces histamine. Histamine is the protein that triggers inflammation and widens your capillaries to allow white blood cells to pass through them so that they can fight foreign invaders.
So, it's the histamine that makes you swell up in itch when you get a bug bite. Just like it makes your eyes and nose itch during pollen season.
We’re not even sure why histamine needs to make you itch in order to do its job. It might just be a body's way of telling you that something's wrong with your skin.