No-See-Um Bites: Why They Itch So Much and What to Do About Them
No-see-um bites are the work of biting midges, flies so small they pass through standard window screens. Treat the bites the way the CDC says to treat mosquito bites: wash with soap and water, ice for 10 minutes, an over-the-counter anti-itch cream, and no scratching. See a provider if a bite looks infected.
You never saw what bit you. That is the defining experience of the no-see-um, and it is right there in the name. By the time the welts show up, the insect responsible is long gone, and most people spend the next day blaming mosquitoes that were never there. This is what actually happened, and what to do about it.
What bit me if I never saw anything?
Almost certainly a biting midge. CDC uses the two names for the same insect: writing about the flies behind the Oropouche outbreak, the agency describes "tiny biting midges, sometimes called 'no-see-ums.'" They are usually less than an eighth of an inch (3 mm) long, and the Illinois Department of Public Health puts the smallest at no more than 1/32 of an inch, which is why you do not see them land and why, in the department's words, "their tiny size allows them to penetrate window and door screens." You will also hear them called punkies or simply gnats.
Location is the other tell. Illinois DPH notes that biting midges "can be serious pests along the shores of oceans, lakes, ponds and rivers, and will bite during the day or at night." Their larvae develop in moist sand or soil, rotting vegetation, tree holes and the damp edges of ponds, marshes and lagoons. If you were bitten at the beach, at a lakeside dinner, or on a porch near a marsh, and you never saw a mosquito, midges are the leading suspect.
What do no-see-um bites look and feel like?
A cluster of small, intensely itchy red bumps, often on exposed ankles, legs, arms, and the back of the neck, and often more of them than you would expect from one sitting outside. There is no separate federal fact sheet for midge bite reactions, but the CDC's explanation of mosquito bites describes the same mechanism: the insect injects saliva as it feeds, and "your body reacts to the saliva resulting in a bump and itching." Reactions vary the same way too. In the CDC's words, "some people have only a mild reaction to a bite or bites. Other people react more strongly, and a large area of swelling, soreness, and redness can occur."
Because midges tend to bite in groups and go unnoticed while they feed, the practical difference from a mosquito bite is count and cluster: several welts in one patch of skin, appearing together, itching out of proportion to their size.
How do you treat no-see-um bites?
The CDC's bite treatment steps, published for mosquito bites, are the standard playbook and they apply here:
- Wash the bite and surrounding area with soap and water.
- Ice it. The CDC says to apply an ice pack for 10 minutes to reduce swelling and itching, and to reapply as needed.
- Baking soda paste can help. A mixture of baking soda and water, applied to the bite, "can help reduce the itch response."
- Use an over-the-counter anti-itch or antihistamine cream to relieve itching, following the product label directions.
And the one instruction that matters most, straight from the CDC: "Do not scratch bites. They can become infected." Scratching is the main way a trivial bite turns into a real problem.
When should you see a doctor?
Two situations. First, infection at the bite itself: the CDC says an infected bite "may appear red, feel warm, or a red streak may spread outward from the bite," and to see a healthcare provider if symptoms worsen.
Second, illness after travel. Biting midges are the primary spreaders of Oropouche virus, and the CDC lists its common symptoms as "fever, severe headache, chills, muscle aches, and joint pains," typically lasting 2 to 7 days and often recurring later. Fewer than 1 in 20 people develop more serious disease, and most people recover within several days to one month. Here is the context that keeps this in proportion: cases found in the United States have been in travelers, and there have been no cases of local transmission. A midge species that could carry the virus does live in the eastern United States, which is why the CDC is watching it. If you develop a fever after travel to an area with Oropouche, mention the travel to a clinician.
How do you stop the next round of bites?
Four moves, all from public health guidance rather than folklore:
- Use a repellent whose label actually lists them. The CDC's advice for midges is specific: look for EPA-registered repellents "labeled for flies, biting flies, or Culicoides (biting midges, punkies, granny nippers, and no-see-ums)."
- Cover up. The CDC advises loose-fitting, long-sleeved shirts and pants.
- Fix the screens. The CDC notes that many common window and door screens do not have holes small enough to stop biting midges, and recommends looking for 20x20 mesh.
- Run a fan. The CDC suggests using fans outdoors to help blow midges away, and Illinois DPH agrees that fans can keep small areas free of the smaller flies, whose flight is weak against air currents.
On actives, Illinois DPH names DEET and picaridin as the ones to look for against biting flies, while noting honestly that repellents "have been found to be less effective against some types of biting flies," so pair whatever you wear with the screens, the fan, and some respect for where midges live.
Longsleeve is an EPA-registered picaridin lotion (EPA Reg. No. 101457-1). It repels mosquitoes and ticks for up to 14 hours, and its accepted federal label carries the claim "Repels biting flies, stable flies, black flies, gnats, chiggers, sand flies and Scottish biting midges (no see-ums) for up to 8 hours." It is fragrance-free, with nine disclosed ingredients. Of the 631 EPA-registered skin repellents in our Repellent Index, 47 carry a stated no-see-um protection time you can read off their federal label.
Short answers
Why do no-see-um bites itch so much?
The itch is your body reacting to the insect's saliva. The CDC explains the mechanism for mosquito bites: saliva goes in as the insect feeds, and the body's reaction produces the bump and the itching. Midges bite in clusters, so you get many reacting welts at once.
How long do no-see-um bites last?
Reaction size and duration vary by person. The CDC notes some people have only a mild reaction while others get a large area of swelling, soreness and redness. Not scratching, per the CDC, is what keeps a bite from getting infected and lasting longer.
Can no-see-ums bite through window screens?
They do not need to bite through them; they fit through the holes. Illinois DPH says their tiny size allows them to penetrate window and door screens, and the CDC recommends 20x20 mesh screens to keep them out.
Do no-see-um bites spread disease?
Biting midges can spread Oropouche virus, and U.S. cases so far have been in travelers, with no local transmission. If you get a fever after travel to an area with Oropouche, see a clinician and mention the travel.
Sources
- CDC, Oropouche Puts Biting Midges Under the Microscope. https://www.cdc.gov/oropouche/stories/midges-under-the-microscope.html
- CDC, Meet the Midge. https://www.cdc.gov/oropouche/stories/meet-the-midge.html
- CDC, About Mosquito Bites. https://www.cdc.gov/mosquitoes/about/about-mosquito-bites.html
- CDC, Symptoms of Oropouche. https://www.cdc.gov/oropouche/symptoms/index.html
- CDC, Preventing Oropouche. https://www.cdc.gov/oropouche/prevention/index.html
- Illinois Department of Public Health, Biting Flies. https://dph.illinois.gov/topics-services/environmental-health-protection/structural-pest-control/biting-flies.html
Last reviewed 2026-08-26 · every claim on this page is sourced above