Why Do Mosquito Bites Itch?

It's your immune system, and maybe your blood type too.

Summer is the season of mosquitoes. And mosquito bites can itch like nothing else. And once you start scratching, it's hard to stop.

"It is the female mosquitoes that bite, and there is some saliva that enters the skin while the mosquito is feasting on its blood meal," said Amy Kassouf, MD, a dermatologist at the Cleveland Clinic. "This is the protein that causes the allergic reaction—and itching," Dr. Kassouf explained.

Basically, our immune systems see the protein as an enemy invader.

"The proteins in the saliva are foreign to your body and cause an immune system response," said Dawn Davis, MD, a dermatologist at the Mayo Clinic in Rochester, Minnesota. "This causes irritation and the local reaction we see as the bug bite," added Dr. Davis.

Our bodies are just particularly sensitive to mosquito bites. Other bugs bite may not have the same impact on your immune system, Dr. Kassouf explained. For example, stings bees and wasps are likely to produce more pain than itching.

Scratching Increases the Itchiness

Scratching a mosquito bite is a double-edged sword—it feels so good for a few seconds, but it also makes the itch sensation way worse.

"When you scratch, you may release more local histamine—the chemical in the skin that causes the swelling and itching—and you may also be spreading the allergen under the skin," said Dr. Kassouf.

If you tend to scratch until you bleed, you're putting yourself at risk for skin infections.

"Scratching a bite opens up the skin, making it more painful or itchy and potentially causing bacterial infections like pyoderma, impetigo, or even cellulitis," cautioned Joaquin C. Brieva, MD, a dermatologist at Northwestern Medicine in Chicago.

Itching Worsens At Night

You're not imagining it—mosquito bites do itch more at night.

"Most people itch more at night because our cortisol levels (our bodies' own anti-inflammatory hormone) are higher in the morning, and also because we are less distracted as we wind down and try to fall asleep," said Dr. Kassouf.

Some People Attract Mosquito Bites

You probably have that friend that gets eaten alive every time they are outside. There are a few reasons why that may be.

Some people may be more prone to get bug bites based on several factors:

  • their natural scent and components of sweat
  • perfume or other added scents
  • the color of their clothing
  • the time of day
  • location (there's more exposure in wooded areas and along landscaping)

And a person's blood type could be to blame. A research study published in 2022 in the journal Scientific Reports found that some types of mosquitos have a preference for feeding on blood type B. The researchers also found that female mosquitos feeding on blood type B lay the highest number of eggs, followed by blood type AB, and blood type O.

Individual Responses To Mosquito Bites Vary

If you've ever wondered why some mosquito bites itch more than others, it totally depends on your body.

"Everyone responds differently to mosquito bites," said Edidiong Kaminska, MD, a dermatologist at Northwestern Medicine in Chicago. While some people may have a minimal reaction, others may experience blisters and extreme swelling. But the most common reaction is simply red, itchy, swollen bumps.

Your reaction depends on your body's immune system. "Reactivity is based on the sensitivity of one's immune system to the bite," Dr. Davis explained.

But some people are prone to develop the big whoppers. "People with atopic traits—eczema, asthma, allergic rhinitis—tend to develop more severe local reactions after mosquito bites," explained Dr. Brieva.

Was this page helpful?
Related Articles