Why Do Mosquito Bites Itch So Much?

That familiar tingle, that little pinch, that harbinger of things to come—if it’s mosquito season, you know it well. It’s a bug bite, and it’s probably about to make you (and your skin) feel pretty itchy. (And you might feel itchy just thinking about feeling itchy. Sorry about that!)

We’ve already explored why some people are more prone to mosquito bites than others— there are lots of reasons, most of which you can’t actually change—but now it’s time to examine why those unavoidable bites can make skin crawl, tickle, and just plain itch.

When it comes to mosquito bites, that telltale itch doesn’t actually come from a bite, it comes from something that’s a fair bit worse: literal blood-sucking. A mosquitos (only female mosquitos do this) uses her needle-like mouthparts (technically called a “proboscis”) to poke around on your skin in order to find the closest blood vessel, which she then uses to suck out blood as a snack (a process that makes her an ectoparasite). The itchiness comes from her saliva, which she injects into her prey both before and during the actual blood extraction process. It’s a clever tool, because her saliva serves as an anticoagulant that keeps the blood flowing during consumption.

The human body responds to foreign intrusions like mosquito saliva by creating histamines, which make the area's blood vessels swell and create a “wheal” on the skin. That wheal is the bump that is so often referred to as a mosquito “bite.” All that swelling often disturbs nearby nerves, which then react by making your skin itch.

Don’t scratch too hard, as it will only make the irritation worse, all while the real invader has long since flown away, blood-filled belly and all.