January 24, 2022

What Happens When a Mosquito Bite Gets Infected?

Learn the proper care and when to seek help after you’ve scratched a bit too much

Close-up shot of a mosquito drawing blood from the skin.

Stop scratching! That’s good advice if you have a mosquito bite … but sometimes it’s easier said than done. That bite itches, right? And it itches a lot.


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Here’s why you need to leave it alone: That little bite can transform into a much larger problem if you continually claw at it. Family nurse practitioner Allison Folger, CNP, says infections can develop if you don’t leave the bite alone.

“Scratching the bite to the point of bleeding can open the door for a bacterial skin infection,” explains Folger. “This commonly occurs in children whose nails are understandably dirty from playing outside, though it also happens in adults.”

Here’s what to do if you (or someone you know) just couldn’t resist that urge to scratch.

What is a mosquito bite?

So, you’re outside enjoying the twilight when you feel a familiar pinch on your arm. A quick glance down reveals the small, winged, blood-sucking culprit behind the pain. Yep … a mosquito.

Odds are, a hand smack quickly follows — but it’s too late. You’ve been bit.

Mosquitoes feed on blood using a long, needle-like mouthpart that pierces skin. As the insect sucks your blood, it secretes saliva that enters your bloodstream. That saliva might as well be called itch juice.


Your body registers the mosquito saliva as an allergen, notes Folger. In response, your immune system sends histamine to the bite spot to remove the allergen. (Basically, think of histamine as your body’s bouncer tossing out unruly visitors.)

But for as much good as the histamine does, it also causes the itching, redness and swelling that you see after a mosquito bite.

What is an infected mosquito bite?

Blame for an infected mosquito bite doesn’t rest solely with the insect. Odds are you played a role in escalating the situation from a mild annoyance and irritation into something requiring extra attention.

The infection, called cellulitis, is from bacteria that enters the punctured skin from your hands. Warning signs include:

  • Swelling of the lymph nodes.
  • Wide-spreading redness around the mosquito bite.
  • Red streaking that extends beyond the initial bite.
  • Pus or drainage.
  • Area feels warm to the touch.
  • Chills.
  • Fever (above 100 degrees Fahrenheit or 37.7 degrees Celsius).

“If you or a child has these signs of infection, it is important to see your doctor,” Folger says.

One easy way to tell if the bite is spreading? Take a pen and draw an outline around the mosquito bite and then check on it later, suggests Folger. That’s a fool-proof, objective way to see if the redness is expanding.


If your doctor confirms the infection is cellulitis, you’ll probably be prescribed antibiotics to kill the bacteria. The most common bacteria causing cellulitis are strep (streptococcus) and staph (staphylococcus).

Home treatment for an infected mosquito bite

Welts from an infected mosquito bite can easily grow to the size of a ping pong ball or mandarin orange. If other symptoms aren’t escalating, Folger recommends the following steps to find some relief.

  1. Clean the bite with soap and water.
  2. Apply an over-the-counter hydrocortisone cream to help reduce the swelling and itching. (This can be followed by calamine lotion, which contains a mild topical anesthetic that may ease the discomfort.)
  3. Use ice packs on the area to help bring the inflammation down.
  4. Reapply the topical medication every four hours as needed.

Your healthcare provider may also recommend using an oral antihistamine (such as Benadryl®), as they’re more effective at providing relief than topical creams.

How to prevent mosquito bites

The best way to avoid a mosquito bite infection (aside from not scratching)? Avoid the bite. To keep those pesky mosquitoes at bay, take these precautions.

  • Cover up with clothing. Bare skin is preferred by mosquitoes. The more covered you are, the less area they have to target.
  • Use insect repellent. Look for products that contain the active ingredients DEET or picaridin, which provide the best protection. Make sure to use any repellent as instructed.
  • Go inside at peak biting hours. Most mosquitoes fly at dusk, especially in wooded areas near water. Activity is lower during the sunnier, hotter times of day.
  • Eliminate mosquito breeding areas. Mosquitoes lay their eggs in standing water. That could mean a puddle that never dries up in your lawn or flowerpots and garbage can lids where water accumulates and sits.

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