A mosquito bite may turn into a fluid-filled blister in some cases. If you also notice symptoms of infection or an allergic reaction, you should contact a doctor for advice on treatments.

Mosquito bites are itchy bumps that occur after female mosquitoes puncture the skin to feed on your blood, which helps them produce eggs.

When they feed, they inject saliva into your skin. Proteins in the saliva cause a mild immunologic reaction, which is what leads to the bump and itchiness.

These bumps are usually puffy and red or pink, and appear a few minutes after you get bitten. However, some people may have a more severe reaction, which can lead to fluid-filled blisters instead of puffy bumps.

Read on to learn more about why this happens and how to treat a mosquito bite that turns into a blister.

Some people have stronger reactions than others to mosquito bites. This reaction can include a lot of swelling, beyond the small bump most people get. When the area becomes swollen, fluid can come up under the top layers of skin and form a blister.

This reaction is natural. While everyone has a mild reaction to mosquito bites, some people are more likely to have quicker reactions than others. There’s nothing you can do or not do to prevent a blister from forming when you get a mosquito bite.

However, children, people with immune system disorders, and people who are bitten by a type of mosquito they haven’t previously been exposed to may have more serious reactions.

In the case of children, this may be because they aren’t desensitized to a mosquito’s saliva like most adults are.

Mosquito bites, including ones that blister, will usually go away by themselves in a few days. While the bite heals, treatments focus on alleviating symptoms such as itchiness.

If the blister is itchy, you can apply an over-the-counter antihistamine or anti-itch lotion before covering it. If the lotion doesn’t work, you can take an oral antihistamine.

Applying an ice pack to the area for 10 minutes at a time can also help with reducing swelling.

Protecting the mosquito bite blister is important. When the blister first forms, gently clean it with soap and water, then cover it with a bandage and petroleum jelly, like Vaseline. Don’t break the blister.

See a doctor if you have signs of:

  • Infection: Pus, sores, fever, and redness or discoloration that spreads from the bite site and doesn’t go away can be symptoms of infection, as well as swelling in your lymph nodes.
  • Mosquito-borne diseases: Symptoms of mosquito-borne diseases can vary. For example, West Nile virus symptoms include headache, joint pain, fever, fatigue, and a general feeling of being unwell.
  • Allergic reaction: An allergic reaction is a medical emergency. You should seek immediate medical help.

Anaphylaxis is a severe reaction to a trigger, such as an allergy, and is potentially life threatening.

Symptoms can develop quickly and include:

  • feeling faint or lightheaded
  • difficulty breathing or wheezing
  • rapid heartbeat
  • confusion
  • anxiety
  • clammy skin
  • collapsing or losing consciousness
  • hives
  • swelling
  • stomach pain, nausea, or vomiting

If you or someone nearby develops these symptoms, you should:

  1. Check to see whether they have an epinephrine pen. If they do, read and follow the instructions to dispense the medication.
  2. Dial 911 (or a local emergency number).
  3. Lay them down. If they have vomited, lay them on their side.
  4. Stay with them until emergency services arrive.

It is possible for someone to need more than one injection with an epinephrine pen. If symptoms do not begin to clear after 5 minutes, give a second injection if one is available.

Common symptoms of a mosquito bite include:

  • itchiness
  • puffy red or pink bump, or multiple bumps, that appear within 30 minutes after the bite
  • dark spot once it heals

Some people may have more serious reactions to mosquito bites. These can include:

  • a lot of swelling and redness or discoloration
  • low-grade fever
  • swollen lymph nodes
  • hives
  • swelling in areas away from bite, like your joints, face, or tongue
  • dizziness
  • trouble breathing (a sign of anaphylaxis that needs emergency medical attention)

Optum Now is owned by RVO Health. By clicking on this link, we may receive a commission. Learn more.

Most bug bites will just create a small bump and itchiness. However, there are other types of bug bites that can blister, such as:

Contact a doctor or Poison Control immediately if you think you might have been bitten by a brown recluse spider. These bites can cause a serious reaction.

It might not be possible to totally avoid mosquito bites, but there are some ways you can reduce your risk of getting bitten. Follow these tips:

  • Wear long pants and long sleeves while outside.
  • Avoid outdoor activities between dusk and dawn, when mosquitoes are most active.
  • Use insect repellent with DEET. Be sure to follow the product’s directions. Be careful not to get them in your eyes or any cuts.
  • Wear a hat that protects your neck and ears.
  • Use mosquito netting if you’re sleeping outdoors.
  • Eliminate standing water near your home, such as in gutters or wading pools. Female mosquitoes lay their eggs in standing water.
  • Keep the doors and windows of your home closed, and make sure screens don’t have any holes.
  • Avoid using heavy perfumes, which may attract mosquitoes.

Learn more about preventing mosquito bites.

Most mosquito bites lead to a puffy, itchy bump. However, in some cases, a fluid-filled blister can develop. Anti-itch lotions or antihistamines can help manage symptoms such as itchiness.

While a blister is a more robust reaction, it’s not usually a sign of a severe reaction unless you have symptoms of an infection or allergic reaction, such as fever or trouble breathing.

Contact a doctor if you have any symptoms of an infection. Seek immediate medical help if a severe allergic reaction happens.