Why Do Mosquito Bites Itch?

It's your immune system response, among other reasons.

Mosquito bites can itch like nothing else. Once you start scratching, it's hard to stop. Why do mosquito bites itch? When you get a bite, the mosquito draws out your blood, while infecting you with proteins in its saliva. Your immune system reacts to that protein by inducing a reaction that causes itching.

What Causes the Itchiness?

The human body is particularly sensitive to mosquito bites versus other bug bites, noted Dr. Kassouf. Mosquito bite symptoms are the result of an immunologic reaction that your body has to the mosquito's saliva.

"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," Amy Kassouf, MD, a dermatologist at the Cleveland Clinic, told Health. "This is the protein that causes the reaction and itching."

Research has found that humans are sensitive to some proteins in mosquito saliva. Other protiens found in their saliva, such as tryptase and leukotrienes, can directly cause itchiness. The immune system is sensitive to some of these proteins and can see them as enemy invaders. As a response, the immune system triggers a release of histamine. Histamine facilitates an immune system response and induces inflammation, which causes itchy symptoms.

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

Does Scratching Worsen the Itchiness?

Scratching a mosquito bite is a double-edged sword. In other words, scratching feels good for a few seconds but also worsens the itchy symptoms.

"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," Dr. Kassouf said. When you itch, the welt may become bigger and itchier the before. 

Also, if you tend to scratch until you bleed, your risk of skin infections increases, Joaquin Brieva, MD, a dermatologist at Northwestern Medicine, told Health.

"Scratching a bite opens up the skin, making it more painful or itchy and potentially causing bacterial infections like pyoderma, impetigo, or even cellulitis," said Dr. Brieva.

Why Itching Gets Worse at Night

The urge to scratch mosquito bites may keep you up at night. No, you're not imagining it. Mosquito bites do itch more after the sun sets.

Cortisol Levels

Cortisol is a hormone that fights inflammation. With mosquito bites, cortisol is what fights the inflammatory response that causes itchiness. When cortisol levels are lower, itchiness increases.

"Most people itch more at night because our cortisol levels are higher in the morning and also because we are less distracted as we wind down and try to fall asleep," Dr. Kassouf said. The lower cortisol levels coupled with the lack of distractions can increase that itchy feeling.

Increase in Blood Flow

Other factors can increase nighttime itching, also called nocturnal pruritus. When you sleep, your body increases blood flow to your skin to release more heat, cooling your body so that you can sleep peacefully. However, the increased circulation to your skin can add to your itching sensation.

Changes in Hormones

Other hormones your body secretes, such as anti-inflammatory corticosteroids, repair tissue damage during the day. Like cortisol, those hormones fluctuate while you're sleeping. Those changing hormones alter how your body reacts to itching.

Anxiety or Depression

People who often have a hard time sleeping may be more prone to anxiety or depression. Those mental health conditions can aggravate the perception of itching. Anxiety and depression can also prolong the time you're awake and scratching.

What Attracts Mosquitos

There are a few reasons why some people attract mosquitos. Research has found that the likelihood of mosquito bites is based on several factors, like:

  • Your natural scent, like your sweat and body odor
  • Your perfume
  • The color of your clothing (i.e., daytime mosquitoes are more attracted to dark clothing than light clothing)
  • Your body temperature (i.e., mosquitos are attracted to high body temperatures)
  • Pregnancy
  • Blood O type
  • Drinking alcohol

Do Mosquito Bites Vary Between People?

Most people simply develop red, itchy, and swollen bumps. If you've ever wondered why some mosquito bites itch more than others, the answer is that it depends on your body.

"Everyone responds differently to mosquito bites," Edidiong Kaminska, MD, a dermatologist based in Chicago, told Health. Some people may have a minimal reaction. In contrast, others may have blisters and extreme swelling.

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

Some conditions, such as the human immunodeficiency virus (HIV) and blood cancers, may also exaggerate your body's response. The same can happen if you are very young or relatively new to mosquito bites.

In fact, some people with significant reactions develop skeeter syndrome. In skeeter syndrome, people can develop severe soreness, redness, itching, pain, or even a low-grade fever after a mosquito bite.

How To Prevent Mosquito Bites

One of the best ways to avoid the aggravating itchiness that comes with mosquito bites is to prevent them. Some ways to prevent mosquito bites include:

  • Avoiding going out at mosquito peak times, which are at dawn and dusk
  • Wearing long sleeves and long pants
  • Considering chemical repellants
  • Mosquito-proofing your home by repairing or replacing screens
  • Dumping out any standing water that is in and around your home

Treatments for Mosquito Bites

If you develop a mosquito bite, try some of the following treatments to reduce symptoms:

  • Elevate the area and apply ice to reduce swelling and pain.
  • Use over-the-counter (OTC) anti-itch lotion on the affected area.
  • Clean blisters and bumps with soap and water without breaking them.
  • Try topical steroids or oral antihistamines if the itch persists.

Consult a healthcare provider if swelling worsens or an infection develops.

A Quick Review

If you have a mosquito bite, your immune system produces an inflammatory response. That response can develop an aggravating amount of itching. 

As hard as it is, avoid scratching. While scratching feels good in the short term, it can lead to more itchiness over a larger area and possibly a skin infection.

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6 Sources
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