Worms in Stool: What They Look Like, What to Do and Which Tests
The essentials
Tiny white threads that wriggle in stool or around the anus, with itching at night, are almost always pinworms: the most common worm infection in the United States, mild and easy to treat. A larger worm, flat white segments or worms after travel need a stool test, because the treatment depends on the species. Keep the worm in a sealed container: the laboratory can identify it.
When are worms in stool an emergency?
Most worm infections cause mild symptoms or none[1][5]. A few situations still need fast care.
When to see a doctor
- Emergency: call 911 for severe belly pain, a swollen belly, repeated vomiting (especially vomiting a worm), no stool or gas for a day or more, a seizure, or trouble breathing. Heavy infections can block the intestine[4], and the pork tapeworm can cause a disease called cysticercosis, which can trigger seizures[5].
- Within 24 to 48 hours if you see a large worm, flat worm segments or blood in the stool, or if the person is a baby, pregnant, or takes steroids or other drugs that weaken immunity: Strongyloides can become life-threatening in these patients[6].
- At your next appointment, or ask a pharmacist, for small white threads with night-time anal itching and no other symptoms, the typical picture of pinworms[10].
What do worms in stool look like?
Most worm infections never show visible worms: the eggs are microscopic[7]. What people see falls into a few patterns.
- Common Something that only looks like a worm. Mucus strands and undigested fruit or vegetable fibers can look like threads. They do not move and they break apart. See mucus in stool.
- Common Pinworms (Enterobius vermicularis, also called threadworms). Small, thin, white worms about the size of a staple[1]. They are the most common worm infection in the United States, mainly in children and their families; the key sign is anal itching at night, when females lay eggs[1].
- Possible Tapeworm segments. Flat, pale pieces, sometimes moving, are the most visible sign of a human tapeworm, caught from raw or undercooked beef or pork. The beef tapeworm can reach 10 meters (33 feet)[5].
- Possible Roundworm (Ascaris). A large worm that looks like an earthworm[10]. It infects an estimated 772 to 892 million people, mostly in tropical areas[4].
- Rare Hookworm, whipworm and Strongyloides. Rarely visible. With Ascaris, soil-transmitted worms infect about 1.5 billion people, 24% of the world population; hookworms cause blood loss and iron deficiency[9]. Strongyloides larvae enter through bare skin[6].
What tests will the doctor order for worms in stool?
Which worm is it? The answer decides the medicine and whether the household needs treatment.
| Test | What it answers | Learn more |
|---|---|---|
| Identification of the worm you bring in | Species of a whole worm or segment; often the fastest answer | Recommended by the CDC for passed worms[4] |
| Tape test (pinworm paddle) | Pinworm eggs on the skin around the anus | Done at home, 3 mornings in a row[2] |
| Stool ova and parasites (O&P) exam | Eggs, larvae and parasites under the microscope; species and amount | Ova and parasites test |
| Complete blood count with eosinophils | Whether the immune cells that fight worms are raised | Eosinophil count, complete blood count |
| Ferritin and iron tests | Iron loss from blood-feeding hookworms | Ferritin levels, iron deficiency tests |
| Strongyloides blood test | Antibodies when larvae are hard to find in stool | Ordered before steroids or transplant[6] |
Received an O&P report or a blood count with a flagged eosinophil line? BloodSense explains each result in plain words and helps you prepare your questions for the doctor.
Get my test results explainedHow do I read the results of these tests?
Pinworms: a normal stool test proves nothing
Pinworm eggs are laid on the skin, not in the stool, so stool samples usually do not contain enough eggs to detect, and there is no blood test for pinworm[3]. Use the tape test instead: clear tape pressed on the skin around the anus on waking, before washing, three mornings in a row[2].
O&P: one negative sample is not the final word
Parasites are not shed every day[7]. In a study of 373 testing episodes, the first sample found the parasite in 75.9% of cases, and a second sample raised this to 92%[11]. For tapeworms, the CDC advises samples on three different days, and eggs appear only 2 to 3 months after infection starts[5]. A positive report names the parasite and how many were seen[7].
Not every parasite on the report is a worm
The O&P also finds invisible single-celled parasites such as Giardia[7]. Without travel or immune problems, family physicians suggest it mainly for diarrhea lasting more than seven days[12]; multiplex stool panels are another option.
High eosinophils: a clue, not a diagnosis
A normal eosinophil count is below 500 cells per microliter[8]. Worms are one cause of a higher count, but so are allergies, asthma and eczema[8]. After tropical travel, low ferritin can point to hookworms[9]; see our guide to anemia.
After treatment: why the second dose matters
Pinworm medicines kill worms but not eggs, so a second dose follows two weeks later, and the whole household is treated together[1]. Roundworm treatment lasts one to three days and is highly effective[4].
What should I note before seeing the doctor?
- The worm itself in a clean, closed container, or a clear photo next to a ruler or coin
- Size, shape and whether it moved
- Itching around the anus, especially at night, and who else at home has it
- Travel abroad in the last 2 years: some worms take a long time to cause symptoms[10]
- Raw or undercooked beef, pork or freshwater fish, walking barefoot on soil
- Steroids or other drugs that lower immunity; pregnancy
Questions to ask your doctor
- Can the lab identify the worm I brought, and do I still need a stool test?
- Should everyone in my household be treated at the same time?
- With my travel history or medicines, should I be tested for Strongyloides?
Frequently asked questions
Why do pinworms keep coming back?
Eggs survive 2 to 3 weeks on bedding and clothes and spread on fingers. Handwashing with soap and treating the whole household together break the cycle[1].
Can I catch worms from my dog or cat?
Rarely. The tapeworm found in pets comes from swallowing infected fleas, which happens to people only in very rare cases[5].
How can I avoid tapeworms from meat?
Cook whole cuts of beef or pork to at least 145 °F (63 °C) with a three-minute rest, and ground meat to at least 160 °F (71 °C), checked with a food thermometer[5].
Related tests and guides
- Ova and parasites testHow the stool parasite exam works and how to read its report.
- Eosinophils blood testWhat a high count means and its many non-parasite causes.
- Mucus in stoolThe most frequent look-alike of worms in the bowl.
- Appendicitis warning signsPinworms are a rare trigger; right-sided pain needs urgent care.
References
- Centers for Disease Control and Prevention. About pinworm infection. cdc.gov (accessed October 28, 2026)
- Centers for Disease Control and Prevention. Diagnosing pinworms. cdc.gov (accessed October 28, 2026)
- Centers for Disease Control and Prevention. Clinical overview of pinworm infection. cdc.gov (accessed October 28, 2026)
- Centers for Disease Control and Prevention. About ascariasis. cdc.gov (accessed October 28, 2026)
- Centers for Disease Control and Prevention. About human tapeworm (taeniasis). cdc.gov (accessed October 28, 2026)
- Centers for Disease Control and Prevention. About Strongyloides. cdc.gov (accessed October 28, 2026)
- MedlinePlus Lab Tests. Ova and parasite test. medlineplus.gov (accessed October 28, 2026)
- MedlinePlus Medical Encyclopedia. Eosinophil count - absolute. medlineplus.gov (accessed October 28, 2026)
- World Health Organization. Soil-transmitted helminth infections (fact sheet). who.int (accessed October 28, 2026)
- NHS. Worms in humans. nhs.uk (accessed October 28, 2026)
- Cartwright CP. Utility of multiple-stool-specimen ova and parasite examinations in a high-prevalence setting. J Clin Microbiol. 1999;37(8):2408-11. doi:10.1128/JCM.37.8.2408-2411.1999 (accessed October 28, 2026)
- Pyzocha N, Cuda A. Common intestinal parasites. Am Fam Physician. 2023;108(5):487-93. aafp.org (accessed October 28, 2026)
This article is general health information. It does not replace a medical examination, diagnosis or treatment. If you have severe belly pain, repeated vomiting or a seizure, seek emergency care without waiting.
