Mosquito bites itch because your body reacts to proteins in the mosquito’s saliva by releasing histamine.
Why they itch
When a mosquito bites, it injects saliva that contains proteins to stop clotting. Your immune system responds by releasing histamine, which causes swelling and itch.
Who is bitten more
Mosquitoes are drawn to carbon dioxide, body heat, sweat and type O blood in some studies.
Relief
- Wash with soap and water.
- Apply a cold pack.
- Use hydrocortisone cream or calamine lotion.
- Take an oral antihistamine.
- Don’t scratch.
Prevention
Use EPA-registered repellents (DEET, picaridin, oil of lemon eucalyptus) and wear long sleeves.
Diseases
Mosquitoes spread malaria, dengue and West Nile virus, killing over 600,000 people a year (WHO).
See a doctor if
There is spreading redness, fever or severe swelling.
Why mosquito bites itch
When a female mosquito bites, she injects saliva that contains proteins to keep blood from clotting and to ease feeding. The immune system recognizes those proteins and releases histamine, causing swelling, redness and itch at the site. The reaction usually starts within minutes and can last a few days. Only females bite, as they need blood protein to develop eggs.
Who is bitten more
- People with type O blood, in some studies, get bitten about 83% more than those with type A.
- People who exhale more carbon dioxide, such as larger people, pregnant women and people exercising.
- People with warmer skin and more sweat.
- Certain skin bacteria and body odors, with genetic components.
- Alcohol drinkers, with a small study showing more bites after one beer.
- Dark clothing attracts more mosquitoes than light.
Bites are not caused by “sweet blood”. There is not good evidence for vitamin B or garlic as repellents.
Relief
- Wash the area with soap and water.
- Apply a cold compress for 10 minutes.
- Use hydrocortisone 1% cream, calamine lotion or an oral antihistamine.
- Avoid scratching, which can cause infection.
- A paste of baking soda and water may soothe the itch.
Prevention
- Use EPA-registered repellents containing DEET (20% to 30%), picaridin (20%), IR3535, oil of lemon eucalyptus (30%) or 2-undecanone. DEET protects for up to 8 hours depending on strength.
- Wear long sleeves and pants, and treat clothing with permethrin.
- Remove standing water in pots, gutters, tires and buckets weekly, where mosquitoes breed.
- Use window screens and air conditioning, and bed nets when traveling.
- Avoid peak biting times at dawn and dusk for most species.
Diseases
Mosquitoes are the deadliest animal for humans. They transmit malaria, which killed about 608,000 people in 2022, according to the WHO, plus dengue, Zika, West Nile virus, chikungunya, yellow fever and eastern equine encephalitis. West Nile virus is the leading mosquito-borne disease in the continental US.
See a doctor if
A bite shows signs of infection (spreading redness, pus, fever), swelling is large (skeeter syndrome), or you develop fever, headache, rash or joint pain after travel or bites. Seek urgent care for trouble breathing or swelling of the face.
Biology of the reaction
Only female mosquitoes bite, because they need blood proteins to develop eggs. While feeding, they inject saliva with anticoagulants and proteins, and the immune system responds by releasing histamine, which causes swelling and itching. Reactions typically appear within minutes and may last 1 to 3 days, and children and people not previously exposed to local species can react more strongly. Mosquitoes are attracted by carbon dioxide from breath, body heat, sweat chemicals such as lactic acid, and skin bacteria. Studies suggest people with type O blood are bitten more than those with type A, though the effect is modest. EPA registered repellents with DEET (20 to 30 percent), picaridin, IR3535 or oil of lemon eucalyptus work for hours. Avoid scratching to reduce infection risk, and use hydrocortisone cream 1 percent or oral antihistamines for relief.
Based on data from the CDC and the EPA
