Why Did My Mosquito Bite Turn into a Blister?
Mosquito bites are itchy bumps that occur after female mosquitoes puncture your 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, 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 to a week. Until they do, you can relieve some of your symptoms.
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 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. For example, West Nile virus symptoms include headache, joint pain, fever, fatigue, and a general feeling of being unwell.
- Allergic reaction. This may be a medical emergency.
It’s possible to have a serious allergic reaction after being bitten by a mosquito. Go to the nearest emergency room if you have a blister and the following symptoms:
Common symptoms of a mosquito bite include:
- puffy red or pink bump, or multiple bumps, that appear a few 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
- low-grade fever
- swollen lymph nodes
- swelling in areas away from bite, like your joints, face, or tongue
- trouble breathing (a sign of anaphylaxis that needs emergency medical attention)
Most bug bites will just create a small bump and itch for a few days. However, there are other types of bug bites that can blister, including:
See a doctor immediately if you think you might have been bitten by a brown recluse spider. These bites can cause a serious reaction.
It might be impossible to totally avoid mosquito bites, but there are some ways you can reduce your risk for 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, icaridin, or oil of lemon eucalyptus. 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.
Most mosquito bites lead to a puffy, itchy bump. However, in some cases, they can turn into blisters.
While this is a more robust reaction, it’s not a sign of a problem unless you have symptoms of an infection or allergic reaction, such as fever or trouble breathing.
See a doctor if you have any symptoms or signs of an allergic reaction or infection.
Last medically reviewed on October 4, 2019
Bug Bites and Stings
- Pictures of different bites and stings
- Types of insect bites
- Risk factors
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Whether you’re in the water, on a mountain trail, or in your backyard, wildlife you encounter have ways of protecting themselves and their territory.
Insects, such as bees, ants, fleas, flies, mosquitoes, wasps, and arachnids, may bite or sting if you get close. Most won’t bother you if you don’t bother them, but knowing what to look for is key.
The initial contact of a bite may be painful. It’s often followed by an allergic reaction to venom deposited into your skin through the insect’s mouth or stinger.
Most bites and stings trigger nothing more than minor discomfort, but some encounters can be deadly, especially if you have severe allergies to the insect venom.
Prevention is the best medicine, so knowing how to recognize and avoid biting and stinging animals or insects is the best way to stay safe.
The animals you should recognize and understand depend very much on where you live or where you’re visiting. Different regions of the United States are home to many of these creatures.
The season also matters. For example, mosquitoes, stinging bees, and wasps tend to come out in full force during the summer.
The form a bite takes depends on what type of insect bit you. Take a look at the photos below to help identify which insect may have caused your bug bite.
Warning: Graphic images ahead.
- A mosquito bite is a small, round, puffy bump that appears soon after you’ve been bitten.
- The bump will become red, hard, swollen, and itchy.
- You may have multiple bites in the same area.
Fire ant bites
This condition is considered a medical emergency. Urgent care may be required.
- Fire ants are small, aggressive, red or black venomous ants with a painful, stinging bite.
- Bites appear as swollen red spots that develop a blister on top.
- Stings burn, itch, and last up to a week.
- They may cause a dangerous, severe allergic reaction in some people, resulting in swelling, generalized itching, and difficulty breathing.
- Flea bites are usually located in clusters on the lower legs and feet.
- The itchy, red bumps are surrounded by a red halo.
- Symptoms begin immediately after you’re bitten.
- The itchy rash is caused by an allergic reaction to the bedbug bite.
- The small rashes have red, swollen areas and dark-red centers.
- Bites may appear in a line or grouped together, usually on areas of the body not covered by clothing, such as the hands, neck, or feet.
- There may be very itchy blisters or hives at the bite site.
- Painful, itchy rashes are caused by an inflammatory reaction at the site of the fly bite.
- Though usually harmless, they may lead to severe allergic reactions or spread insect-borne diseases.
- Take precautions when traveling to endemic countries by wearing long-sleeved shirts and pants and using bug spray.
- Head lice, pubic lice (“crabs”), and body lice are different species of parasitic lice that affect humans.
- They feed on blood and cause an itchy immune reaction at the site of their bites.
- Adult lice are gray/tan six-legged insects about the size of a tiny sesame seed.
- Nits (eggs) and nymphs (baby lice) can only be seen as very tiny specks that may look like dandruff.
- Painful, itchy rashes may be caused by an immune response to the bites of tiny mite larva.
- Bites appear as welts, blisters, pimples, or hives.
- Bites will generally appear in groups and are extremely itchy.
- Chigger bites may be grouped in skin folds or near areas where clothing fits tightly.
- Bites can cause pain or swelling at the bite area.
- They may also lead to a rash, burning sensation, blisters, or difficulty breathing.
- The tick often remains attached to the skin for a long time.
- Bites rarely appear in groups.
- Symptoms may take 4 to 6 weeks to appear.
- The extremely itchy rash may be pimply, made up of tiny blisters, or scaly.
- They may cause raised, white, or flesh-toned lines.
This condition is considered a medical emergency. Urgent care may be required.
- Most spiders don’t pose a threat to humans, and their bites are harmless or mildly irritating like a bee sting.
- Dangerous spiders include brown recluse, black widow, funnel web spider (Australia), and wandering spider (South America).
- A single raised papule, pustule, or wheal may appear at the site of the bite followed by redness and tenderness.
- The bite will appear as two small puncture marks.
- Severe allergic reactions to a spider bite may require medical attention.
Brown recluse spider
- This is a shy, brown- or tan-colored spider with a violin-shaped patch and six paired eyes, two in the front and two sets of two on either side of the head.
- It likes to hide in quiet, dark places like closets and bookshelves and is native to the South and South Central regions of the United States.
- Nonaggressive, it will only bite humans if it’s being crushed between skin and a hard surface.
- Redness appears with a central, white blister at the site of the bite.
- Moderate to severe pain and itching at the site of the bite occurs 2 to 8 hours after the spider has injected its venom.
- Rare complications include fever, body aches, nausea, vomiting, hemolytic anemia, rhabdomyolysis, and kidney failure.
Black widow spider
This condition is considered a medical emergency. Urgent care may be required.
- This spider is plump, black, and shiny, with an hourglass-shaped red mark on its abdomen.
- It’s nonaggressive and will only bite if it’s being crushed.
- Bites cause muscle pain and spasms in the arms, legs, abdomen, and back.
- Tremor, sweating, weakness, chills, nausea, vomiting, and headache are other symptoms.
- The bite area is red with a white center.
- The venom of this common household spider isn’t considered toxic to humans.
- Bites are generally harmless and cause only minor pain, swelling, and sometimes muscle twitches.
- A single red area appears with a tender central nodule.
- Itching, burning, or stinging may occur at the site of the bite.
- This large (up to 2 inches long) fuzzy, gray/brown spider is native to many parts of the United States.
- Nonaggressive, it will bite if it feels threatened.
- A tender, itchy red bump appears that heals in 7 to 10 days.
- These large (1-inch long) blood-sucking flies are most active in the daylight hours.
- An instant, sharp burning sensation occurs when a horsefly bites.
- Itchiness, redness, swelling, and bruising may also occur at the bite location.
- Pain, redness, swelling, or itching occurs at the site of the sting.
- A white spot appears where the stinger punctured the skin.
- Unlike bumblebees and carpenter bees, honeybees can only sting once due to their barbed stinger that can remain in the skin.
- These thin wasps have black-and-yellow stripes and long dark wings.
- Aggressive, a yellow jacket may sting multiple times.
- Swelling, tenderness, itchiness, or redness may occur near the area that’s been stung.
- Sharp pain, redness, swelling, and itching or burning occurs at the sting site.
- A raised welt appears around the sting site.
- Wasps can be aggressive and are capable of stinging multiple times.
- These are eight-legged arachnids with large pincers and long, segmented, stinger-tipped tails carried in a forward curve over their backs.
- Many species with variable levels of toxicity can be found all over the world.
- Intense pain, tingling, numbness, and swelling occurs around the sting.
- Rare symptoms include breathing difficulties, muscle twitching, drooling, sweating, nausea, vomiting, increased heart rate, restlessness, excitability, and inconsolable crying.
- Severe symptoms are more likely in infants and children than adults.
Here are some bugs that can be more dangerous than others.
Biting insects, arachnids, and other bugs
Many bugs bite, but only a few do so intentionally. Most bites are relatively harmless, leaving just an itchy patch of skin behind. But some bites can carry disease. Deer ticks, for example, typically carry Lyme disease.
Intentional biters include:
Many larger insects and other bugs won’t seek you out but will bite if handled.
Some spiders have poisonous fangs. Poisonous spiders found in the United States include:
Insects will sting humans only to defend against a perceived threat. Typically, a bee or stinging ant’s stinger will be accompanied by a small amount of venom.
When injected into your skin, the venom causes most of the itching and pain associated with the sting. It can also cause an allergic reaction.
Common stinging insects in the United States include:
Scorpions have a reputation for stinging. Many species have barbed tails equipped with poison, some strong enough to kill a human.
The most venomous species of scorpion native to the United States is the Arizona bark scorpion.
The venom injected into your body from the bite or sting of an insect will cause your immune system to respond. Often, your body’s immediate response will include redness and swelling at the site of the bite or sting.
Minor delayed reactions include itching and soreness.
If you’re very sensitive to an insect’s venom, bites and stings can cause a potentially fatal condition called anaphylactic shock. This can cause the throat to tighten and make breathing difficult or cause low blood pressure.
Some bites and stings may cause illnesses when venom contains infectious agents.
Anyone can be bitten or stung by an insect, and bites and stings are very common. You’re at greater risk if you spend a lot of time outdoors, especially in rural or wooded locations.
Children and older adults may have more severe reactions to bites and stings.
If you’re bitten or stung, you may see or feel the insect on your skin during the attack. Some people don’t notice the insect and may not be aware of a bite or sting until one or more of the following symptoms emerge:
- redness or rash
- pain in the affected area or in the muscles
- heat on and around the site of the bite or sting
- numbness or tingling in the affected area
Symptoms of a severe reaction requiring immediate medical treatment include:
- difficulty breathing
- nausea or vomiting
- muscle spasms
- rapid heartbeat
- swelling of the lips and throat
- loss of consciousness
If you feel ill or experience flu-like symptoms in the days following an insect bite, see your doctor for tests to rule out infections or diseases you may have contracted from the insect.
Many people are aware they’ve been bitten or stung because they see the insect shortly after the attack.
Although you shouldn’t further provoke an attacking insect, try to preserve the insect if it dies following the bite or sting. Its identity may help your doctor properly diagnose your symptoms.
This is especially important for a spider bite, as some species have dangerously potent venom.
The majority of bites and stings can be treated at home, especially if your reaction is mild.
To treat a bite or sting:
- Remove the stinger if it’s lodged in your skin.
- Wash the affected area.
- Apply an ice pack to reduce pain and swelling.
You may also want to consider applying a thin paste of baking soda and water to the sting to calm the itching.
Call 911 or your local emergency services number immediately if symptoms of a severe reaction are present.
First aid instructions while waiting for paramedics to arrive include:
- loosening the victim’s clothing
- laying them on their side
- performing CPR if breathing or heartbeat stops
If you believe a spider of the black widow or brown recluse variety has bitten you, seek emergency medical treatment immediately even if symptoms seem minor or haven’t emerged.
Scorpion bites also should be treated in the emergency room, regardless of symptoms
Most bites and stings heal by themselves after several days of mild discomfort.
Monitor the affected site for signs of infection. Contact your doctor if the wound appears to be getting worse or hasn’t healed after several weeks.
Bites and stings that cause severe reactions can be fatal if they aren’t treated immediately.
Once you’ve experienced a severe allergic reaction, your doctor will likely prescribe an epinephrine auto-injector. Epinephrine is a hormone that can prevent anaphylactic shock.
Carry the auto-injector with you at all times to reverse the reaction immediately following a bite or sting
Use caution when near nests or hives containing aggressive insects. Hire professionals who have the proper safety equipment to remove a nest or hive.
When spending time outside, take preventive measures, such as:
- wearing hats and clothing that provide full coverage
- wearing neutral colors and avoiding floral patterns
- avoiding perfume and scented lotion
- keeping food and drinks covered
- using citronella candles or insect repellent
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