The scenario plays out every summer. You’re enjoying a beautiful day outside, when suddenly, a red, itchy welt raises up on your skin. Without thinking – or even knowing why mosquito bites itch – you instinctively start to scratch. Your skin reddens, the bite gets itchier and you start to notice two more red welts appearing from new bites. Your day just got a lot more annoying. So, why does this happen? Why are mosquito bites so itchy?

When a mosquito bites you, a few things happen. For starters, the mosquito uses her (all mosquitoes that bite are female) feeding stylets to pierce your skin. The stylet consists of a pair of maxillae and a pair of mandibles. Once she breaks through your skin, the mosquito quickly searches for a blood vessel, and then begins the blood siphoning process. Mosquitoes can suck your blood with such force that tiny blood vessels collapse or rupture. At the same time your blood is pumping out of your body, the mosquito pumps saliva in.

This saliva acts as an anticoagulant, which prevents your blood from clotting at the site of the puncture. This allows the mosquito to feed quickly, giving her a better chance of stealing away with your blood before you notice and splat her on your arm. This saliva is specifically why mosquito bites itch – you have an allergic reaction to it, resulting in the telltale bump and itching associated with mosquito bites.

The mosquito saliva flows into your body through one tube (the hypopharynx), while another tube (the labrum) is used for pumping your blood up to the waiting mosquito. The saliva contains enzymes and proteins that bypass your body’s natural coagulation system. These anticoagulants – along with up to 19 other enzymes and proteins – directly cause the allergic reaction in your body.

Your body’s immune system responds to these allergens by releasing histamines. Some scientists believe that your very first mosquito bite introduced these allergens to your body and sensitized you to the components of the saliva. This sensitization is responsible for your body sending immunoglobulins to the mosquito bite. Immunoglobulins break down connective tissue and mast cells, which actually release the histamines that make you itch. Mast cells help heal wounds and defend against pathogens, but they play a big part in allergic reactions and inflammation. The histamines they release are commonly combated with antihistamines, which work to stop the itch.

New research points to a more complicated response from the body that includes a ‟histamine-independent peripheral pathway.” This involves mast cells as well, but theorizes that substances other than histamines are released, which then cause peripheral neurons to signal the central nervous system (CNS). The CNS interprets these signals and sends them to the brain, which lets you know that the bite itches.

The science behind why mosquito bites itch is interesting to say the least, but that doesn’t help you once you’ve been bitten. The bite will still puff up, turn red and itch. Chances are, you’ll oblige the itch and scratch until your heart’s content. Unfortunately, you might also scratch until you break skin, depositing dirt or other contaminants into the open wound. This can lead to bacterial infections.

And even if you don’t cause your own infection, mosquitoes might do the dirty work for you. These flying pests carry and transmit multiple diseases – some deadly – such as malaria, dengue, Chikungunya, yellow fever and mosquito-borne encephalitis. Now that you know what causes mosquito bites to itch, and what might happen, do something about it. Call a pest management professional to help lower the population of mosquitoes around your property so you and your family can enjoy the great outdoors.