Written from CDC, WHO, MedlinePlus, and Mayo Clinic information available in October 2026. Use it to understand what you are seeing, then let a clinician confirm what is actually going on.
Here is the surprising part first: most people with intestinal worms feel completely fine. According to the CDC, people with light infections usually have no symptoms at all, and that holds for roundworm, whipworm, and hookworm alike. Worms tend to announce themselves only when there are a lot of them, when they are a particular kind, or when they are moving through the body on their way to the gut.
When the signs of intestinal worms do show up, they tend to cluster in a few places: in the bathroom, in your belly, in your energy levels and blood tests, on your skin, and occasionally in your lungs. This field guide is organized that way, by where you are likely to notice something, so you can match what you are seeing to what might be causing it. Then we cover what different worms look like, who is most at risk, how doctors confirm an infection, the conditions that commonly get mistaken for worms, and the situations that need urgent care.
One ground rule before we start. Seeing a sign in this list does not mean you have worms, and not seeing any does not rule them out. Only a test, and sometimes a doctor’s judgment based on where you have lived or traveled, can answer that question.
In the bathroom
The bathroom is where most people first suspect something is wrong. These are the most direct signs, and the ones most likely to lead to a diagnosis.
Seeing a worm or worm pieces in your stool
This is the most definite sign, and it depends on the type of worm:
- Pinworms look like tiny, thin, white threads, about the size of a staple according to the CDC. They are often seen on the surface of stool, on toilet paper, or around the anus at night.
- Roundworms (Ascaris) are large. Mayo Clinic notes adult females can exceed 15 inches (40 cm) and are about a quarter inch wide, so a passed roundworm looks like a pale, earthworm-like strand. MedlinePlus notes they can also be vomited up or, rarely, come out of the nose or mouth.
- Tapeworm segments (called proglottids) look like flat, white or cream-colored pieces, a bit like grains of rice or small pieces of pasta. The CDC says seeing these segments leave through the anus or in stool is the most noticeable sign of beef or pork tapeworm. Segments may even move.
Hookworms and whipworms are small and live attached to the gut wall, so people rarely see them.
Itching around the anus, especially at night
An itchy bottom that gets worse at night is the classic sign of pinworm. Female pinworms crawl out of the anus at night to lay eggs on the surrounding skin, which causes intense itching. The CDC’s pinworm page notes that people may also sleep poorly or feel restless, and that worms occasionally reach the vaginal area and cause irritation. Scratching can break the skin and lead to a bacterial infection.
Diarrhea, blood, or mucus in stool
Heavier worm infections can cause loose stools. Whipworm, in particular, can cause diarrhea with blood and mucus, and the WHO notes it can lead to dysentery. In heavy infections, children may develop rectal prolapse, where part of the rectum pushes out through the anus. Bloody stool always deserves a medical visit, whatever the cause.
In your gut
Belly symptoms are among the most common signs of intestinal worms, but they are also very general. Many everyday conditions cause the same feelings, which is why these signs alone rarely point clearly to worms.
Common gut symptoms
- Abdominal pain or discomfort, often vague and hard to pin down
- Bloating and gas
- Nausea or vomiting
- Diarrhea, sometimes alternating with constipation
- Loss of appetite, or sometimes increased hunger
- Unexplained weight loss
The CDC’s tapeworm page lists stomach pain, reduced appetite, weight loss, and nausea as the usual digestive symptoms when a tapeworm causes any at all. The CDC page on Strongyloides describes abdominal pain, bloating, heartburn, and occasional diarrhea or constipation.
When the gut gets blocked
A heavy roundworm infection can do something more serious. Large numbers of worms can tangle together and block the intestine, especially in children. Mayo Clinic describes severe abdominal pain, vomiting, and constipation as signs of a large worm load. This is a medical emergency, covered in the urgent section below.
In your energy and blood
Some worms do their damage quietly by draining nutrients. These signs often show up as fatigue and on blood tests before anyone thinks of worms.
Iron-deficiency anemia from hookworm
Hookworms attach to the lining of the small intestine and feed on blood. MedlinePlus explains that this steady blood loss can lead to iron-deficiency anemia and protein loss. Over months, that shows up as:
- Tiredness and low energy
- Pale skin, gums, or inner eyelids
- Shortness of breath with activity
- Dizziness or headaches
- Poor concentration
- In severe cases, swelling from protein loss
The WHO highlights that this anemia is a particular problem for adolescent girls and women of reproductive age, who are already at higher risk of low iron. If your iron is low, our guide on how to increase hemoglobin covers diet and treatment, but if hookworm is the cause, the worms need to be treated too or the blood loss will continue.
Vitamin B12 deficiency from fish tapeworm
The fish tapeworm (Diphyllobothrium), which people catch from raw or undercooked fish, absorbs vitamin B12 from the gut. The CDC notes this can cause B12 deficiency and anemia. B12 deficiency can also cause tingling or numbness in the hands and feet, memory trouble, and a sore, smooth tongue. The CDC says the largest species can grow up to 30 feet long.
General malnutrition
Several types of worm compete with you for nutrients or damage the gut lining enough to reduce absorption. The WHO links soil-transmitted worms to malnutrition, especially in children who already have limited food.
On your skin
The skin is an entry point for some worms and a place where the immune system’s reaction can show up.
Ground itch (hookworm)
Hookworm larvae live in soil contaminated with human feces and can burrow through bare skin, usually the feet. MedlinePlus notes that this can cause an itchy rash at the entry site, known as ground itch. It typically appears as small, very itchy red bumps or blisters, often between the toes or on the soles, and fades in a few days as the larvae move on.
Larva currens (Strongyloides)
Strongyloides can cause a distinctive rash called larva currens, meaning “running larva.” It appears as a raised, red, very itchy line that can move quickly, often across the buttocks, thighs, or lower back, sometimes several centimeters per hour. It tends to come and go over months or years because this worm can reinfect the same person repeatedly. The CDC lists rashes among the signs of more severe infection.
Hives and general itching
Some people with worm infections develop hives or a generalized itchy rash as part of an allergic-type response. MedlinePlus lists skin rash among possible roundworm symptoms. This is a nonspecific sign that could have many other causes.
Skin damage around the anus
As mentioned above, pinworm scratching can cause red, raw, irritated skin around the anus, which can become infected.
In your lungs
This one surprises people. Roundworm and hookworm larvae, and Strongyloides larvae, travel through the lungs before settling in the gut. Their passage can cause temporary lung symptoms.
Löffler syndrome with roundworm
When roundworm larvae pass through the lungs, they can trigger what doctors call Löffler syndrome, a short-lived inflammation with high levels of eosinophils, a type of white blood cell. Mayo Clinic describes this lung phase as lasting about 10 to 14 days. MedlinePlus lists these possible symptoms:
- Dry cough, which may bring up a little blood
- Wheezing that can mimic asthma
- Shortness of breath
- Low-grade fever
Because these symptoms come before worms reach the gut, stool tests can be negative at this stage. A doctor may suspect the cause from a chest X-ray, raised eosinophils on blood tests, and travel or exposure history.
Other worms
Hookworm larvae can cause a mild cough during their lung passage. The CDC lists dry cough as a possible Strongyloides symptom. In people with weakened immune systems, Strongyloides can spread to the lungs in large numbers and cause serious breathing problems.
Signs of intestinal worms in children
Children are the most likely group to get intestinal worms, and the signs of intestinal worms in kids can build slowly over months rather than appear overnight.
Growth and development
The WHO says heavier worm infections can impair children’s growth and physical development, and the CDC notes they can slow both physical and cognitive growth. Signs parents might notice include:
- Falling behind on height or weight growth charts
- A swollen belly paired with thin arms and legs
- Low appetite or picky eating that is new
- Frequent tiredness or lack of interest in play
School and behavior
Anemia and poor sleep can both affect concentration. Children with pinworm itch at night may be irritable and tired during the day. A child who is restless at bedtime, wakes often, and scratches their bottom is a common pinworm picture.
What about teeth grinding and bedwetting?
You may hear that worms cause teeth grinding or bedwetting. This belief is common in many cultures, including in India and the US. There is no strong evidence that intestinal worms cause teeth grinding. Pinworms may play a role in bedwetting in some girls, possibly because worms irritate the urinary area, but bedwetting has many more common causes, such as normal development, deep sleep, constipation, or a urinary tract infection. Do not assume worms are the cause without a test.
Daycare and household spread
Pinworm spreads easily among young children through hands, bedding, and shared toys. The CDC notes infections often spread to several people in the same household or childcare setting. If one child has pinworms, others in the house may need treatment. Our guide to albendazole for pinworms explains the usual approach, and our article on albendazole dosage for children covers how dosing is set by weight and age.
Signs of intestinal worms in adults
Adults in the US are less likely to have worms than children, and the signs of intestinal worms in adults are often subtle, so certain patterns are worth knowing.
- Travelers and immigrants. Adults who have lived in or traveled to areas with poor sanitation may carry worms for years, especially Strongyloides, which can persist for decades without symptoms.
- Parents and caregivers. Adults caring for children with pinworms often catch them too.
- Unexplained anemia. In adults, iron-deficiency anemia is usually blamed on menstrual or gut bleeding. In people from endemic areas, hookworm should be on the list.
- Raw fish and undercooked meat. Sushi, ceviche, and rare pork or beef are linked to fish, pork, and beef tapeworms.
- Steroid treatment risk. The CDC warns that Strongyloides can become severe or life-threatening in people who take corticosteroids or have weakened immune systems. Adults from endemic regions who need long-term steroids may be screened first.
- Seizures. In adults from areas where pork tapeworm is common, a new seizure can be a sign of neurocysticercosis, when larval cysts reach the brain. This is not an intestinal worm in the usual sense, but it begins with the same tapeworm.
Worm ID chart
This chart pulls together the most common worms people in the US and India encounter. It is a simplified guide, not a diagnostic tool.
| Worm | How you get it | Key sign | What it looks like |
|---|---|---|---|
| Pinworm (Enterobius) | Swallowing eggs from hands, bedding, or surfaces | Itchy bottom at night | Thin, white, about staple length |
| Roundworm (Ascaris) | Eating food or water contaminated with eggs from soil | Often none; cough in lung phase; worm in stool or vomit | Large, pale, earthworm-like, can be over a foot long |
| Hookworm | Larvae burrowing through bare skin; one type also swallowed | Ground itch, fatigue, iron-deficiency anemia | Tiny, rarely seen |
| Whipworm (Trichuris) | Swallowing eggs from contaminated soil or produce | Diarrhea with blood or mucus in heavy infection | Small, whip-shaped, rarely seen |
| Strongyloides (threadworm) | Larvae burrowing through skin | Larva currens rash, belly pain, can persist for years | Microscopic |
| Beef or pork tapeworm (Taenia) | Undercooked beef or pork | Flat white segments in stool or underwear | Flat, ribbon-like segments |
| Fish tapeworm (Diphyllobothrium) | Raw or undercooked fish | B12 deficiency, often no symptoms | Long, flat segments |
For a closer look at tapeworm treatment, see our guide to albendazole for tapeworm.
Who is at risk
Worm infections follow exposure. The biggest risk factors are:
- Living in or traveling to areas with poor sanitation. The WHO estimates about 1.5 billion people, roughly 24% of the world’s population, have soil-transmitted worm infections, concentrated in warm, humid regions with limited sanitation.
- Walking barefoot on soil that might be contaminated with human feces. This is how hookworm and Strongyloides enter the body.
- Eating unwashed or unpeeled produce, or drinking untreated water, in areas where human waste reaches soil or water. The CDC lists both as routes for roundworm and whipworm.
- Eating raw or undercooked meat or fish. The CDC notes cooking fish to an internal temperature of at least 145°F (63°C), or freezing it properly, kills the fish tapeworm; salting, smoking, and pickling do not.
- Daycare, schools, and crowded households. These are ideal for pinworm spread.
- Poor handwashing, nail biting, and thumb sucking, especially in children.
- Certain jobs, such as farming, mining, or tea picking in endemic regions, which the WHO lists as higher risk.
In many countries with high worm burdens, including India, children receive regular deworming tablets at school without being tested first. Our article on mass deworming programs explains how those campaigns work.
How doctors confirm it
If you notice possible signs of intestinal worms, the next step is testing. The right test depends on which worm is likely.
Stool ova and parasite (O&P) test
This is the main test for most intestinal worms. A lab looks at your stool under a microscope for eggs, larvae, or worm segments. Because eggs are not passed in every bowel movement, doctors often ask for more than one sample on different days. The CDC notes this especially for fish tapeworm, where eggs may be scarce.
The tape test for pinworm
Pinworm eggs are laid on the skin around the anus, not in stool, so a stool test often misses them. Instead, a piece of clear tape is pressed against the skin around the anus first thing in the morning, before bathing or using the toilet, and then examined under a microscope. The CDC also notes a provider can look for worms around the anus 2 to 3 hours after the person falls asleep, or examine material under the fingernails.
Blood tests
- Complete blood count (CBC): can show anemia and raised eosinophils, a type of white blood cell that rises with many worm infections.
- Iron studies and B12 levels: help when hookworm or fish tapeworm is suspected.
- Serology (antibody tests): useful for worms that are hard to find in stool, such as Strongyloides, or for tissue infections like cysticercosis.
Imaging
An abdominal X-ray or ultrasound may be used if a doctor suspects intestinal blockage from roundworms. Brain imaging (CT or MRI) is used if neurocysticercosis is suspected.
Signs it’s NOT worms
Many of the signs of intestinal worms in this guide overlap with common conditions. These are frequent look-alikes:
| Symptom | Common non-worm causes |
|---|---|
| Anal itching | Hemorrhoids, eczema, fungal infection, sweat and moisture, harsh soaps, incomplete wiping |
| Bloating and belly pain | Irritable bowel syndrome (IBS), lactose intolerance, constipation, gas from diet |
| Diarrhea | Viral or bacterial gut infection, food intolerance, medicines, IBS |
| Blood in stool | Hemorrhoids, anal fissure, inflammatory bowel disease, polyps |
| Fatigue and anemia | Heavy periods, low iron diet, thyroid disease, chronic illness |
| White threads in stool | Undigested food fibers, such as bananas or vegetable skins, or mucus |
| Teeth grinding and bedwetting in children | Normal development, stress, sleep issues, constipation, urinary infection |
A common trap is seeing white, string-like bits in stool and assuming worms. Undigested food and mucus can look surprisingly similar. If unsure, a stool sample or a clear photo shown to your clinician can help settle it. Blood in stool, unexplained weight loss, and persistent changes in bowel habits should be checked by a doctor regardless, because they can signal conditions more serious than worms.
When it’s urgent
Most worm infections are not emergencies, but some situations need prompt care. Get medical help right away, or call 911 in the US, for:
- Severe or worsening abdominal pain, especially with a swollen belly
- Repeated vomiting, particularly if a worm has been vomited or the person cannot keep fluids down
- No bowel movements or gas along with belly pain, a possible sign of intestinal blockage
- A seizure, especially a first seizure in someone from or who has traveled to an area where pork tapeworm is common
- Yellowing of the skin or eyes, which can happen if a roundworm blocks a bile duct
- Severe shortness of breath or coughing up significant blood
- High fever, confusion, or widespread rash in someone on steroids or with a weakened immune system, which can signal severe Strongyloides infection
- Signs of severe anemia, such as chest pain, fainting, or a racing heart
For non-urgent but persistent signs, such as an itchy bottom at night, unexplained fatigue, or a worm seen in stool, book a regular appointment. Treatment is usually simple. Albendazole is one of the most common medicines used; you can read about how it works in our overview of what albendazole is, and how it compares to the other common option in albendazole vs mebendazole.
Frequently asked questions
Can you have worms and not know it?
Yes, and it is common. The CDC says people with light infections of roundworm, whipworm, or hookworm usually have no symptoms. Strongyloides can live in the body for decades with few or no signs.
What do worms in human stool look like?
It depends on the worm. Pinworms look like tiny white threads. Roundworms are large, pale, and earthworm-like. Tapeworm pieces are flat, white, rice- or pasta-like segments. Undigested food and mucus can look similar, so a test is the only way to be sure.
Why does pinworm itching get worse at night?
Female pinworms crawl out of the anus at night to lay eggs on the surrounding skin. This causes the itching, which is why symptoms tend to peak at bedtime and early morning.
Can worms cause tiredness?
Yes. Hookworms cause blood loss that can lead to iron-deficiency anemia, and fish tapeworm can cause vitamin B12 deficiency. Both can leave you feeling tired and weak. Many other things cause fatigue, so blood tests help identify the real cause.
Do worms cause teeth grinding in children?
There is no strong evidence that worms cause teeth grinding. It is a common belief, but grinding is usually linked to normal development, stress, or sleep issues. Pinworm itching can disturb sleep, though.
Should the whole family be treated if one person has worms?
For pinworm, doctors often treat everyone in the household at the same time, because it spreads so easily. For other worms, family members may be tested if they share the same exposure. Your doctor will advise based on the type of worm.
