Pinworms are tiny, white, thread-like worms that live in the human intestine. Female adults measure about 8 to 13 millimeters long (roughly the length of a staple), while males are smaller at 2 to 5 millimeters. They’re visible to the naked eye, and if you’re reading this, you’re probably trying to figure out whether something you spotted on your child, in their underwear, or in the toilet is actually a worm.
Size, Color, and Shape
A live pinworm looks like a small piece of white thread or dental floss. The body is smooth, pale white, and slightly tapered at both ends. Females are the ones you’re most likely to see because they migrate out of the intestine at night to lay eggs around the anus. Their pointed, pin-shaped tail is actually what gives the worm its name. Males are roughly half the size of females and rarely seen outside the body.
When alive, pinworms may wiggle or curl slightly. Dead worms tend to look like tiny white threads stuck to skin, clothing, or bedding. They can sometimes appear slightly yellowish after they’ve dried out. Because of their size, you can see them without a magnifying glass, but you do need to look carefully. A single worm sitting on dark-colored underwear or pajamas is easier to spot than one on light fabric or skin.
Where and When to Look
The best time to check is 2 to 3 hours after the person falls asleep. That’s when female pinworms crawl out of the intestine to deposit eggs on the skin around the anus. Use a flashlight and look at the skin folds in the perianal area. You may see one or more small white worms, sometimes moving. They can also show up on underwear, pajama bottoms, or bed sheets around the same time.
You’re less likely to spot pinworms in stool. While worms occasionally appear on the surface of a bowel movement, they don’t usually pass in large numbers that way. The nighttime skin check is far more reliable for visual identification.
What Pinworm Eggs Look Like
Pinworm eggs are invisible to the naked eye. Each egg measures about 50 to 60 micrometers long (roughly half the width of a human hair) and has an oval shape that’s flattened on one side, almost like a tiny football pressed against a table. You won’t see them on skin or clothing, which is why diagnosis typically relies on a tape test rather than just looking.
The standard method involves pressing a piece of clear adhesive tape against the skin around the anus first thing in the morning, before bathing. The tape picks up any eggs deposited overnight, and a healthcare provider examines it under a microscope. The CDC recommends collecting samples on three consecutive mornings for the most accurate result, since egg-laying doesn’t happen every single night. If an infection is present, eggs and sometimes adult worms will be visible on the tape under magnification.
Pinworms vs. Threads, Lint, and Other Lookalikes
The most common thing mistaken for a pinworm is a small piece of white thread or clothing fiber. Here’s how to tell the difference:
- Movement: A live pinworm wiggles. Thread doesn’t. If you see any motion at all, it’s likely a worm.
- Shape: Pinworms taper to a point at one or both ends. Thread tends to have a uniform width or frayed ends.
- Texture: A worm looks smooth and slightly translucent, almost like a thin piece of wet noodle. Cotton or synthetic fibers look matte and fuzzy under close inspection.
- Context: If the white thread-like object is on the skin near the anus and the person (usually a child) has been complaining of itching at night, pinworms are a strong possibility.
Pinworms are also sometimes confused with other intestinal parasites. However, most other worms that infect humans are either much larger (like roundworms, which can reach 15 to 35 centimeters) or much thinner and harder to see without a microscope. The combination of small size, white color, and location near the anus is distinctive to pinworms.
Symptoms That Confirm What You’re Seeing
If you’re spotting something that matches the description above and the person also has intense itching around the anus, especially at night, that’s the classic pattern. The itching is caused by the female worm depositing eggs, which triggers an immune response in the surrounding skin. Children may scratch in their sleep, become restless, or have trouble staying asleep without knowing why.
Some people with pinworms have no symptoms at all, particularly with light infections. Others notice irritability, loss of appetite, or mild stomach discomfort. In girls, worms occasionally migrate to the vaginal area and cause itching or irritation there as well.
Who Gets Pinworms
Pinworm infection is the most common intestinal worm infection in developed countries, and it overwhelmingly affects children. Kids in group settings like preschools and elementary schools are at highest risk because the eggs spread so easily: a child scratches, picks up microscopic eggs under their fingernails, and transfers them to surfaces, toys, or other children. Eggs can survive on surfaces for two to three weeks.
A large study tracking nearly 28,000 preschool children from 2019 to 2024 found an overall infection rate under 1%, with rates declining over the six-year period. Older preschool-age children had a higher likelihood of infection than younger ones, likely because of more social contact and hand-to-mouth behavior. The infections also tended to cluster within specific classrooms and facilities rather than being evenly spread, which underscores how quickly pinworms transmit in shared spaces.
Adults can get pinworms too, usually by picking up eggs from an infected child in their household. The entire family is often treated at the same time to break the cycle of reinfection, even if only one person has visible symptoms.
What Happens After You Spot Them
If you’ve seen what looks like a pinworm, the next step is straightforward. A healthcare provider can confirm the diagnosis with the tape test described above or simply by hearing your description of what you saw. Treatment is a single dose of oral medication, repeated two weeks later to catch any worms that hatched after the first dose. The infection clears quickly once treated.
In the meantime, washing bedding, pajamas, and underwear in hot water helps reduce egg counts in your home. Encourage thorough handwashing, especially before meals and after using the bathroom. Keeping fingernails trimmed short makes it harder for eggs to hide underneath them. These steps won’t cure the infection on their own, but they reduce the chances of reinfection after treatment.