How to Treat a Mosquito Bite

Wash the bite and the skin around it with soap and water, hold an ice pack on it for 10 minutes to reduce swelling and itching, and use an over-the-counter anti-itch or antihistamine cream. Do not scratch it. Those are the CDC's steps. See a healthcare provider if symptoms worsen.

That is the whole treatment for a normal bite. The harder part is telling a harmless reaction from an infection.

Why does a mosquito bite itch?

The CDC describes the mechanics plainly. When a mosquito bites you, it pierces the skin using a special mouthpart called a proboscis to suck up blood, and as it feeds it injects saliva into your skin. Your body reacts to the saliva, and that reaction is the bump and the itching.

A 2022 review in Frontiers in Immunology describes histamine as a key player, either histamine present in mosquito saliva itself or histamine released when mast cells are activated by IgE primed against saliva proteins. Histamine binds to receptors on nerve endings and drives local vasodilation and edema, which is what forms the wheal. Other salivary components, including tryptase and leukotrienes, may induce non-histaminergic itch.

The reaction runs in phases. That review describes an immediate reaction, a round wheal 2 to 10 mm across with redness peaking in 20 to 30 minutes, then a delayed reaction of itchy papules the same size that peak in 24 to 36 hours and fade over several days. The CDC lists what you may see: a puffy reddish bump minutes after the bite, a hard, itchy, reddish-brown bump a day or so later, small blisters instead of hard bumps, or dark spots that look like bruises.

People react differently, and the CDC says so outright. Some have only a mild reaction, others react more strongly with a large area of swelling, soreness, and redness.

What does the CDC recommend for treating a mosquito bite?

1. Wash the bite and surrounding area with soap and water.
2. Apply an ice pack for 10 minutes to reduce swelling and itching. Reapply as needed.
3. Apply a mixture of baking soda and water, which the CDC says can help reduce the itch response. Mix 1 tablespoon of baking soda with just enough water to create a paste, apply it to the bite, wait 10 minutes, then wash it off.
4. Use an over-the-counter anti-itch or antihistamine cream to help relieve itching, following the product label directions.

The cold is doing real work. The Frontiers review notes that cooling reduces itch through TRPM8, an ion channel in peripheral nerve endings, inhibiting both histaminergic and non-histaminergic itch pathways. The American Academy of Pediatrics adds options in its mosquito bite guidance on HealthyChildren.org: 1% hydrocortisone cream three times a day until the itch is gone, ice in a wet washcloth for 20 minutes as a fallback, and firm, steady pressure on the bite for 10 seconds with a fingernail or pen cap. For severe itching it mentions an oral allergy medicine, with age limits on the page.

Why does scratching make it worse?

The CDC's instruction is one line: do not scratch bites, they can become infected. The AAP explains the mechanism. Infections of mosquito bites are not common, and they most often occur in bites that have been scratched or picked at, usually starting with an infected sore or scab. For kids, the AAP advice is to cut the fingernails short and help the child not to scratch. The Frontiers review lists the consequences of scratching as scarring, hyperpigmentation, and superinfection.

How can you tell if a mosquito bite is infected?

The CDC gives three markers: an infected bite may appear red, feel warm, or a red streak may spread outward from the bite. See a healthcare provider if symptoms worsen.

The trap is that a large, red, angry-looking bite is usually not an infection. The AAP describes large local reactions as very common in young children, with redness reaching 2 to 4 inches (5 to 10 cm) that starts right after the bite and may keep getting larger for 2 to 3 days. Per the AAP that is still normal: a harmless local allergic reaction to mosquito saliva, not a sign of infection. The feature that separates them is pain, because infections of mosquito bites are painful to touch.

Timing separates them too. The AAP states that any redness starting in the first 24 hours is always a reaction to the bite. The infections the AAP names are impetigo, which gives sores, soft scabs, and pus; cellulitis, where redness spreads out from the bite and the red area hurts to touch; and lymphangitis, a red line running up the arm or leg, which the AAP calls more serious because the infection can reach the bloodstream.

One lookalike is worth naming. The Frontiers review describes Skeeter syndrome, a large local inflammatory reaction of redness, warmth, swelling, and itching that can come with fever and swollen lymph nodes. It mimics cellulitis, and the review says the difference is duration: Skeeter syndrome occurs within hours of a bite and resolves in 3 to 10 days.

What does normal healing look like?

The AAP's expectations for an ordinary bite: most itch for 3 or 4 days, any pinkness or redness lasts 3 or 4 days, and swelling may last 7 days. Bites on the upper face can cause severe swelling around the eye, which the AAP says does not hurt vision and is harmless.

How do you avoid the next one?

The CDC's mosquito prevention guidance starts with repellent. Use EPA-registered insect repellents with one of six active ingredients: DEET, picaridin (KBR 3023 or icaridin outside the United States), IR3535, oil of lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone. Look for an EPA registration number (EPA Reg. No.) on the label, which the CDC says means the company provided EPA with technical information on the effectiveness of the product. Follow the label instructions, reapply as directed, and if you use sunscreen, apply it first.

For children the CDC adds: no OLE or PMD on children under 3 years old, no repellent on a child's hands, eyes, mouth, cuts, or irritated skin, and apply it to your own hands first before a child's face. Past repellent, the CDC recommends loose-fitting long sleeves and pants, permethrin-treated clothing and gear (never on skin), window and door screens, and emptying anything that holds water once a week.

If the thing that bit you is still attached, that is a different procedure. See how to remove a tick and Lyme disease prevention.

When should you see a doctor about a mosquito bite?

The CDC's baseline is to see a healthcare provider if symptoms worsen. The AAP's guidance is more granular.

• Call 911 if a life-threatening allergic reaction is suspected, which the AAP describes as sudden onset of trouble breathing or swallowing, or if the person cannot be woken up.
• Go to the ER for someone hard to wake up, confused, barely able to walk, or with a stiff neck.
• Call a doctor or seek care now for a spreading red area or streak with fever, or if the person looks or acts very sick.
• Contact a doctor within 24 hours for painful spreading redness starting more than 48 hours after the bite, redness still growing more than 72 hours after, or an unexplained fever after recent travel outside the country to a high-risk area.
• Contact a doctor during office hours for an infected-looking scab no better with antibiotic ointment, or severe itching no better after 24 hours of steroid cream.

Fever after mosquito exposure is its own category, because mosquitoes spread germs through bites that can make you sick. For West Nile virus, the CDC says symptoms usually start 2 to 6 days after being bitten by an infected mosquito but can start anywhere from 2 to 14 days, that most people (80%) infected develop no symptoms, and that about 20% develop flu-like symptoms such as fever with headache, body aches, joint pains, vomiting, diarrhea, or rash. Seek immediate medical attention, the CDC says, for high fever, neck stiffness, muscle weakness, confusion, or tremors.

If you have traveled, dengue belongs on the list. The CDC says the most common symptom is fever with aches and pains, nausea or vomiting, or rash, and to see a provider if you have those symptoms and have recently been in an area with risk of dengue. Severe dengue is a medical emergency: go immediately to a clinic or emergency room for belly pain or tenderness, repeated vomiting, bleeding from the nose or gums, blood in vomit or stool, or extreme tiredness or restlessness.

What does a severe reaction look like?

The CDC says severe reactions can occur in children, in adults bitten by mosquito species they have not been exposed to previously, and in people with immune system disorders. The more severe reactions it lists are a large area of swelling and redness, low-grade fever, hives, and swollen lymph nodes.

True anaphylaxis from a mosquito bite is extraordinarily rare. The Frontiers review notes that IgE-mediated reactions to mosquito saliva range from large local reactions to very rare life-threatening anaphylaxis presenting as presyncope, hypotension, and syncope, and that fewer than thirty anaphylactic reactions to mosquitoes have been reported worldwide. Rare is not never, and the AAP threshold stands: sudden trouble breathing or swallowing means 911.

About Longsleeve

Longsleeve is an EPA-registered picaridin lotion (EPA Reg. No. 101457-1). It repels mosquitoes and ticks for up to 14 hours. It is fragrance-free, with nine disclosed ingredients.

None of this replaces medical advice. If a bite is getting worse instead of better, or you run a fever after being bitten, call your doctor and mention the bite.

Common questions

Is a huge swollen mosquito bite an allergic reaction?

Usually not the dangerous kind. The AAP says a large hive at the bite does not mean your child has an allergy, and calls large local reactions with 2 to 4 inches of redness a harmless local allergic reaction to mosquito saliva, not a sign of infection.

Does baking soda actually help?

The CDC includes it and says the mixture can help reduce the itch response: 1 tablespoon of baking soda with just enough water to make a paste, applied for 10 minutes, then washed off. The Frontiers review lists sodium bicarbonate among options with a paucity of supporting evidence for specific alleviation of mosquito bite symptoms, so treat it as cheap to try rather than proven.

When does a bite stop being normal?

Per the AAP, call a doctor if the bite looks infected, meaning the redness gets larger after 48 hours or there is pus discharge, or if the bite becomes very painful.

Sources

1. CDC, About Mosquito Bites. https://www.cdc.gov/mosquitoes/about/about-mosquito-bites.html
2. CDC, Preventing Mosquito Bites. https://www.cdc.gov/mosquitoes/prevention/index.html
3. CDC, Symptoms of West Nile. https://www.cdc.gov/west-nile-virus/signs-symptoms/index.html
4. CDC, Symptoms of Dengue and Testing. https://www.cdc.gov/dengue/signs-symptoms/index.html
5. American Academy of Pediatrics, HealthyChildren.org Symptom Checker: Mosquito Bite. https://www.healthychildren.org/English/tips-tools/symptom-checker/Pages/symptomviewer.aspx?symptom=Mosquito+Bite
6. Vander Does A, Labib A, Yosipovitch G. Update on mosquito bite reaction: Itch and hypersensitivity, pathophysiology, prevention, and treatment. Frontiers in Immunology, 2022;13:1024559. https://pmc.ncbi.nlm.nih.gov/articles/PMC9532860/

Last reviewed 2026-08-06 · every claim on this page is sourced above