Why Do Mosquito Bites Itch?

The Science Behind Itchy Bug Bites

Mosquito biting.
Just what makes a mosquito bite feel so itchy?. Getty Images/Oxford Scientific/Roger Eritja

Most people experience some kind of skin reaction after being bitten by a mosquito. The pain of the bite and the red bump that follows is tolerable, but the persistent itching is enough to drive you crazy. Why do mosquito bites itch?!

Why Mosquitoes Bite

Mosquitoes aren't biting you for their own entertainment, nor are they doing it in self defense (as is usually the case when bees sting). Both male and female mosquitoes get nourishment from nectar, not from blood.

 

Mosquitoes require protein and iron to develop their eggs, two substances they can get both from blood. Only the female mosquito feeds on blood, and she only does so when she's developing eggs. 

For a small insect such as a mosquito, biting a large mammal like you is a risky proposition. A good number of mosquitoes get slapped and killed in their pursuit of blood, after all. So mama mosquito only resorts to drinking blood when she requires proteins to produce healthy, viable eggs. 

If the mosquito wants to survive to produce offspring, she's got to be fast and efficient about getting that blood meal. She'll seek out a blood vessel that's pumping well, and let your veins do the work of filling her belly quickly so she can escape before you have time to react.

Why Mosquito Bites Itch

Though we commonly call them mosquito bites, she's not really biting you at all. The mosquito pierces the upper layer of your skin with her proboscis, a straw-like mouthpart that allows her to drink fluids.

Once she breaks through your epidermis, the mosquito uses her proboscis to search for a pumping blood vessel in the dermal layer underneath.

When the mosquito locates a good vessel, she releases some of her saliva into the wound. Mosquito saliva contains anti-coagulants that keeps your blood flowing until she is finished with her meal.

Now your immune system realizes something is going on, and springs into action. Your plasma cells produce immunoglobulins (antibodies) and send them to the area of the bite. These antibodies cause your mast cells to release histamines to combat the foreign substance. The histamine reaches the area under attack, causing blood vessels there to swell. It's the action of the histamine that causes the red bump, called a wheal.

But what about the itching? When the blood vessels expand, the swelling irritates nerves in the area. You feel this nerve irritation as an itchy sensation.

Recent studies of mosquito bite reactions in mice suggest there may be something else causing the itch. The mast cells may release another non-histamine substance that causes peripheral neurons to send itch signals to the brain.

How to Stop Mosquito Bites from Itching

As should be obvious, the best way to cure the itch of a mosquito bite is to avoid getting bitten in the first place. Whenever possible, wear long sleeves and pants when you're outdoors and mosquitoes are active. Studies show that insect repellants containing DEET are effective against mosquitoes, so do yourself a favor and apply some bug spray before venturing outside.

If you've already been bitten, your best defense against mosquito bite itch is a good antihistamine (which literally means "against histamine"). Take a dose of your favorite over-the-counter oral antihistamine to calm the itch and irritation. You can also use a topical antihistamine product on the bites for immediate relief.

Sources:

  • Physician's Guide to Arthropods of Medical Importance, 6th edition, by Jerome Goddard.
  • The Insects: An Outline of Entomology, 3rd edition, by P. J. Gullan and P. S. Cranston
  • "Mosquito Bite Itch," by Kathryn Eckert, Ross Lab, Pittsburgh Center for Pain Research, University of Pittsburgh. Accessed online November 2, 2015.
  • "Medical Mythbusters - Mosquito Bites!,"by John A. Vaughn, MD, and Angela Walker, Med IV, Ohio State University. Accessed online November 22, 2016.
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Hadley, Debbie. "Why Do Mosquito Bites Itch?" ThoughtCo, Sep. 25, 2017, thoughtco.com/why-do-mosquito-bites-itch-1968392. Hadley, Debbie. (2017, September 25). Why Do Mosquito Bites Itch? Retrieved from https://www.thoughtco.com/why-do-mosquito-bites-itch-1968392 Hadley, Debbie. "Why Do Mosquito Bites Itch?" ThoughtCo. https://www.thoughtco.com/why-do-mosquito-bites-itch-1968392 (accessed December 11, 2017).