Why No-See-Um Bites Itch So Much, How Long They Last, and How to Treat Them
Short answer: A 2018 paper in Parasites and Vectors describes the midge as a pool feeder: it cuts the skin, feeds from a small pool of blood, and leaves saliva in the wound. In more than 90 percent of people, the immune system becomes sensitized to those saliva proteins, and the itch is that hypersensitivity reaction.
Why are no-see-um bites so itchy?
No-see-um bites itch because of how the insect feeds and what it leaves behind. No-see-ums are biting midges; the CDC uses both names for the same insect. A mosquito feeds from a blood vessel. A Culicoides biting midge is a pool feeder: a 2018 paper in Parasites and Vectors describes its mouthparts piercing the outer skin and doing significant mechanical damage to the dermis beneath, so that blood collects in a little pool it drinks from.
Its saliva goes into that wound carrying, per the same paper, anti-hemostatic factors, protease inhibitors, and immune modulatory proteins.
Your body notices. A 2020 review in Allergologie Select reports that bites from blood-feeding insects routinely sensitize people to salivary proteins and cause local hypersensitivity reactions in more than 90 percent of the population. The CDC puts it simply for mosquitoes: the insect injects saliva as it feeds, your body reacts, and you get a bump and itching. The itch is your immune system answering a foreign protein.
The review also notes that midge species feeding on humans can cause type 1 and type 4 hypersensitivity reactions in the skin, and it describes bites taking more than one form: the fast welt and the slower, harder bump.
Why do no-see-um bites show up days later?
Because a bite can produce a late reaction as well as an immediate one, and the late one develops 12 to 24 hours after the bite and then persists for several days, according to a 2020 review in Allergologie Select. The Allergologie Select review describes both: in most people a bite causes either an immediate reaction, wheals, redness and itching within minutes, or a late reaction, a firm papule that develops 12 to 24 hours after the bite and persists for several days.
The late reaction is what fools people. You spend Saturday on the sand, notice almost nothing, and wake up Sunday with a crop of hard, itchy bumps. The review reports these as the two patterns most people get, one or the other, and it notes separately that midge species feeding on humans can cause both type 1 and type 4 hypersensitivity reactions in the skin.
How long do no-see-um bites last?
The late-reaction bump persists for several days, according to the Allergologie Select review; the immediate welt is transient and fades sooner.
The outer bound is one unusual case. A 2010 case report in the American Journal of Tropical Medicine and Hygiene, titled Bullous Leg Lesions Caused by Culicoides Midges after Travel in the Amazon Basin, describes lesions that stabilized by the third day and had largely resolved by 14 days with minimal scarring. That was a severe blistering reaction, covered below, and no forecast for a typical bite.
Why do two people heal so differently? The CDC's note on mosquito bites applies: some people have only a mild reaction, others a large area of swelling, soreness and redness. The person matters as much as the insect.
What is the fastest way to treat no-see-um bites?
Wash it, ice it, and keep your hands off it. The CDC's bite-care protocol is written for mosquito bites and is the sensible place to start for a midge bite:
- Wash the bite and the surrounding area with soap and water.
- Apply an ice pack for 10 minutes to reduce swelling and itching. Reapply as needed.
- Apply a baking soda and water paste, which the CDC says can help reduce the itch response.
- Use an over-the-counter anti-itch or antihistamine cream, following the label directions.
- Do not scratch. Scratched bites can become infected.
If you want a natural treatment, ice and a baking soda paste are the ones with a public health agency behind them. Our mosquito bite treatment guide goes deeper.
Then watch the bite. The CDC says an infected bite may look red, feel warm, or show a red streak spreading outward. If symptoms worsen, see a healthcare provider.
No-see-um bites vs mosquito bites: how to tell
Judge by the insect and the setting; the bumps themselves overlap, since the Allergologie Select review describes the immediate welt and delayed papule for blood-feeding insect bites generally. Not sure what bit you? Our black fly bites and chigger bites guides cover two other suspects.
| Attribute | No-see-um (biting midge) | Mosquito |
|---|---|---|
| How it feeds | Pool feeder: mouthparts pierce the epidermis and damage vessels in the dermis; it feeds from the pool of blood that forms (Parasites and Vectors, 2018) | Feeds from a blood vessel (Parasites and Vectors, 2018) |
| Size | No more than 1/32 of an inch (Illinois DPH); about 1 mm and noiseless (Am J Trop Med Hyg, 2010); usually under an eighth of an inch, 3 mm (CDC) | Not addressed by our sources |
| Window screens | Crawls through most screens that otherwise keep out mosquitoes (CDC) | Kept out by most screens (CDC) |
| Bed nets | Standard bed nets are less effective; the insects pass through the netting (WHO) | Not addressed by our sources |
| Time of day | Day or night (Illinois DPH); timing varies by species (CDC) | Day and night (CDC) |
| Reaction timing | Immediate wheal within minutes, or a firm papule 12 to 24 hours later lasting several days (Allergologie Select, 2020, on insect bites generally) | Same two patterns |
Bitten indoors, behind screens, no mosquito in sight? Suspect a midge.
Do no-see-ums come through window screens?
Yes. The CDC states that because of their small size, biting midges can crawl through most screens that otherwise keep out mosquitoes, which explains waking up bitten with no bug in sight.
The fix has a number. The CDC's Oropouche prevention page says many common window and door screens do not have holes small enough to stop biting midges and recommends 20x20 mesh. Illinois DPH agrees: standard household screen mesh is not fine enough for the tiniest biting flies and should be replaced with finer mesh where they are a problem.
Bed nets share the weakness: the World Health Organization notes standard nets are less effective against biting midges, which pass through the netting, while fine mesh nets and residual insecticide sprayed on the walls of infested buildings have been shown to be effective.
Do no-see-um bites blister?
Blistering is documented but unusual, and not what to expect. The clearest account is a 2010 case report in the American Journal of Tropical Medicine and Hygiene, Bullous Leg Lesions Caused by Culicoides Midges after Travel in the Amazon Basin: multiple blisters up to 4.5 cm across developed on the legs, with swelling around them. The lesions stabilized by the third day and had largely resolved by 14 days with minimal scarring.
The mechanism is the ordinary one at full volume: midge species that feed on humans can cause type 1 and type 4 hypersensitivity reactions in the skin, per the Allergologie Select review. The Illinois Department of Public Health, writing about biting flies as a group and not midges specifically, warns that in sensitive individuals the fly's saliva can trigger life-threatening allergic reactions. The CDC's infection signs apply: redness, warmth, or a red streak spreading outward. See a healthcare provider if symptoms worsen.
Where are no-see-ums found?
Near water, in damp ground, and, on the Illinois Department of Public Health's own pest pages, in Illinois. The Illinois Department of Public Health calls biting midges serious pests along the shores of oceans, lakes, ponds and rivers, biting day or night. Their larvae live in moist sand or soil, rotting vegetation, tree holes and other damp spots, often at the edges of ponds, marshes and lagoons.
The state's structural pest control page treats midges as a household problem, down to replacing window screens with finer mesh. The CDC adds that a midge species that could carry Oropouche virus lives in the eastern United States.
The name fits: the 2010 case report calls Culicoides midges approximately 1 mm and noiseless, easy to overlook, and the CDC says they can be out at different times of day, varying by species. Beach bites have another common suspect, covered in our sand flea bites guide. For identification and biology, start with our guide to no-see-ums.
Can no-see-ums make you sick?
They can carry a virus, and the CDC reports no local transmission in the United States. The CDC says Oropouche virus is spread mostly by tiny biting midges, also called no-see-ums, though some mosquitoes can spread it as well. Common symptoms, per the CDC, are fever, severe headache, chills, muscle aches and joint pains, typically lasting 2 to 7 days but often reoccurring later.
Two CDC facts frame the risk at home: a midge species that could carry the virus lives in the eastern United States, and cases have been found in travelers returning to the United States, with no local transmission. If you develop a fever, severe headache or joint pain after a trip where midges bit you, call a clinician and tell them what bit you.
How do you keep no-see-ums from biting?
Use a repellent labeled for biting midges, cover up, move the air, and fix the screens.
Repellent. The CDC advises EPA-registered repellents labeled for flies, biting flies, or Culicoides, the genus covering biting midges, punkies, granny nippers and no-see-ums. The Illinois Department of Public Health adds a caveat: repellents effective against mosquitoes have been found less effective against some types of biting flies, and it names DEET or picaridin as the best active ingredients. Our guide to no-see-um repellents goes deeper.
Clothing. The CDC says loose-fitting, long-sleeved shirts and pants. Illinois DPH goes further for biting flies: heavy-duty, light-colored clothing, including long-sleeve shirts, long pants and hats.
Air and screens. The CDC suggests fans outdoors to blow biting midges away, and 20x20 mesh indoors, since many common screens have holes too large to stop them.
The label. The EPA's rule for every repellent: always read the product label before using it. That is where a product's covered pests and claimed hours live.
Common questions
How do you get rid of no-see-um bites fast?
Start with the CDC's bite-care steps: wash the bite and the surrounding skin 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 as the label directs. Then leave it alone. The CDC's warning is that scratched bites can become infected.
How long does a no-see-um bite last?
The delayed reaction, a firm bump that appears 12 to 24 hours after the bite, persists for several days, according to a 2020 review in Allergologie Select. The longest documented course we found is a single severe case in the American Journal of Tropical Medicine and Hygiene, where blistering lesions had largely resolved by 14 days. That was one unusual case, and the outer edge of what has been documented.
Why am I waking up with bites but no bugs?
Probably because biting midges got in and you never saw them. The CDC says they are small enough to crawl through most screens that otherwise keep out mosquitoes. A 2010 case report describes them as roughly 1 mm long and noiseless, so they are easy to miss. The CDC recommends 20x20 mesh screens to keep them out of the house.
Are no-see-um bites worse than mosquito bites?
No source we use ranks them, so we will not either. What is documented is a difference in how they feed. A 2018 paper in Parasites and Vectors describes mosquitoes as vessel feeders and Culicoides midges as pool feeders whose mouthparts damage the dermis and leave small pools of blood under the skin. The reaction patterns, an immediate welt or a delayed hard bump, apply to insect bites generally.
Can no-see-ums make you sick?
The CDC says biting midges can spread Oropouche virus. Common symptoms are fever, severe headache, chills, muscle aches and joint pains, typically lasting 2 to 7 days and often reoccurring later. The CDC has found cases in travelers returning to the United States and reports no cases of local transmission. If you get a fever after midge bites on a trip, see a clinician.
About Longsleeve
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.
None of this is medical advice. If you develop a rash or a fever after a bite, call your doctor and tell them what bit you.
More Longsleeve in your Google feed:
Sources
- Parasites and Vectors, 2018, peer-reviewed article on Culicoides biting midges (PubMed Central PMC6011595). https://pmc.ncbi.nlm.nih.gov/articles/PMC6011595/
- Allergologie Select, 2020, peer-reviewed review of insect bite hypersensitivity (PubMed Central PMC7709451). https://pmc.ncbi.nlm.nih.gov/articles/PMC7709451/
- CDC, Midges Under the Microscope (Oropouche). https://www.cdc.gov/oropouche/stories/midges-under-the-microscope.html
- CDC, About Mosquito Bites. https://www.cdc.gov/mosquitoes/about/about-mosquito-bites.html
- American Journal of Tropical Medicine and Hygiene, 2010, 83(3), case report on Culicoides bites (PubMed Central PMC2929031). https://pmc.ncbi.nlm.nih.gov/articles/PMC2929031/
- Illinois Department of Public Health, Biting Flies. https://dph.illinois.gov/topics-services/environmental-health-protection/structural-pest-control/biting-flies.html
- CDC, Meet the Midge (Oropouche). https://www.cdc.gov/oropouche/stories/meet-the-midge.html
- World Health Organization, Oropouche virus disease fact sheet. https://www.who.int/news-room/fact-sheets/detail/oropouche-virus-disease
- CDC, About Mosquitoes. https://www.cdc.gov/mosquitoes/about/index.html
- CDC, Oropouche: Prevention. https://www.cdc.gov/oropouche/prevention/index.html
- CDC, Oropouche: Symptoms. https://www.cdc.gov/oropouche/symptoms/index.html
- EPA, Using Insect Repellents Safely and Effectively. https://www.epa.gov/insect-repellents/using-insect-repellents-safely-and-effectively
Last reviewed 2026-09-03 · every claim on this page is sourced above