A bug bite itches because your body releases histamine in response to proteins in the insect’s saliva or venom.
The cause
When an insect bites, it injects saliva with proteins. Your immune system releases histamine, which dilates blood vessels, sends fluid to the area and triggers nerve endings that make you itch.
What helps
- Wash with soap and water.
- Use a cold compress.
- Apply hydrocortisone cream or calamine lotion.
- Take an oral antihistamine.
Don’t
Scratch, which can cause infection.
See a doctor
If you see spreading redness, pus, fever or signs of an allergic reaction.
The bite process
When a mosquito bites, it injects saliva that contains proteins to prevent blood from clotting. The immune system recognizes these proteins as foreign and releases histamine, causing itching, redness and swelling.
Reaction differences
Reactions vary by person, species and previous exposure. Children often react more strongly to a new insect, and repeated exposure can reduce the reaction over time.
Other insects
- Fleas: small clusters of bites, often on ankles.
- Bed bugs: lines or clusters of itchy bumps on exposed skin at night.
- Ticks: usually painless; watch for rash or fever.
- Ants: stinging, sometimes with pustules, as with fire ants.
- Chiggers: very itchy red spots around the waist or ankles.
Relief
- Wash with soap and water.
- Apply a cold compress for 10 minutes.
- Use hydrocortisone 1% cream or calamine lotion.
- Take an oral antihistamine like cetirizine for many bites.
- A paste of baking soda and water may soothe.
Do not
Avoid scratching, which can break the skin and cause infection (impetigo or cellulitis). Keep nails short, and cover with a bandage if needed.
Prevention
- Use repellents with DEET (20% to 30%), picaridin, IR3535 or oil of lemon eucalyptus, as recommended by the CDC.
- Wear long sleeves and pants in bug areas.
- Remove standing water where mosquitoes breed.
- Use window screens and bed nets.
See a doctor if
Redness spreads, there is pus, fever or swollen lymph nodes. Seek emergency care for hives, swelling of the face or throat, trouble breathing or dizziness after a bite, which may mean anaphylaxis.
Immune reaction details
When a mosquito, flea or other insect bites, it injects saliva with proteins that prevent clotting and dull pain. The body detects these proteins as foreign, and mast cells release histamine, which widens blood vessels and stimulates itch nerves, causing a red, raised bump. Some people react more strongly, with large swollen areas called Skeeter syndrome, and children often have bigger reactions. Bed bug bites form clusters or lines, flea bites occur around the ankles, and fire ants cause painful pustules. Itching usually peaks within a day and fades in a few days.
Relief and warning signs
Wash the area, apply a cold pack for 10 minutes, and use 1 percent hydrocortisone cream, calamine lotion or an oral antihistamine to reduce itching. Avoid scratching, which can lead to infection such as impetigo. Insect repellents with DEET, picaridin or oil of lemon eucalyptus reduce bites. Ticks should be removed with fine tweezers pulling straight up, and Lyme disease affects an estimated 476,000 Americans treated each year, according to the CDC, often with an expanding rash. See a doctor for spreading redness, fever, pus, bullseye rash or swelling of the face or throat.
Based on data from the CDC and the American Academy of Dermatology
