Pinworms look like tiny, white, thread-like worms on or near the anus. They are most visible at night, and the females (the ones you’re most likely to spot) measure 8 to 13 millimeters long, roughly the length of a staple. If you’re checking yourself or a child and see small white worms that are wiggling, you’re almost certainly looking at pinworms.
Size, Shape, and Color
Female pinworms are the ones you’ll typically see around the anus because they crawl out of the intestine to lay eggs on the surrounding skin. They are white, very thin (about 0.3 to 0.5 mm wide), and have a distinctive pointed tail, which is where the name “pinworm” comes from. At 8 to 13 mm long, they’re clearly visible to the naked eye and look like short pieces of white thread.
Male pinworms are much smaller, only 2 to 5 mm long and barely 0.1 to 0.2 mm wide. You’re far less likely to notice them. Males have a blunt, rounded tail rather than a pointed one, but at their tiny size, that detail is hard to see without magnification.
How to Check at Night
The CDC recommends checking 2 to 3 hours after the person falls asleep. Female pinworms leave the intestine through the anus while the person is sleeping and deposit eggs on the surrounding skin. This migration is what causes the intense itching that’s the hallmark symptom of a pinworm infection.
To check, shine a flashlight directly on the skin around the anus. The worms appear as tiny white threads against the skin. They may be still or slowly moving. If you don’t see anything on the first night, check again for two or three additional nights, since the worms don’t always emerge every night.
How to Tell Them Apart From Lint or Fibers
White clothing fibers, toilet paper residue, and lint can look confusingly similar at first glance. The key difference is movement. A pinworm will wiggle or slowly crawl across the skin, while a fiber stays completely still. Pinworms also have a consistent shape: smooth, slightly tapered, and uniformly white. Fibers tend to be irregular, fuzzy at the edges, or inconsistent in width. If you’re unsure, watch for 10 to 15 seconds. A living worm will eventually move.
Pinworm Eggs Are Not Visible
While the adult worms are easy to spot, their eggs are microscopic. You won’t see them on the skin no matter how closely you look. This matters because a person can have a pinworm infection with eggs present around the anus but no visible adult worms at the time you check. The standard diagnostic method is the “tape test”: pressing a piece of clear adhesive tape against the skin near the anus first thing in the morning (before bathing or using the toilet), then bringing the tape to a healthcare provider who examines it under a microscope for eggs. Eggs can also collect under fingernails from scratching, which is another place providers sometimes check.
Signs on the Skin Around the Anus
Even when you don’t catch the worms in the act, there are secondary clues. The skin around the anus may appear red or irritated from repeated scratching, especially in children who scratch in their sleep. You might notice small scratch marks or a mild rash. In some cases the skin looks raw or slightly broken. These signs alone don’t confirm pinworms, since other conditions cause perianal itching, but combined with nighttime itching that disrupts sleep, they strongly suggest an infection worth testing for.
What You Might See in Stool
Pinworms sometimes appear in stool, though this is less common than spotting them on the skin. In a bowel movement, they look the same: tiny white threads, sometimes still moving. They’re easy to miss if you’re not looking closely because of their small size. Checking the skin at night remains the more reliable method for visual confirmation.
How Pinworm Infections Spread
Pinworm infection is the most common worm infection in the United States, and it spreads easily. When a person scratches the itchy area, microscopic eggs get trapped under the fingernails and transfer to surfaces, food, clothing, or other people. Eggs can also become airborne when shaking out bedding. The entire cycle from swallowing eggs to new adults laying eggs takes about 2 to 6 weeks, which is why reinfection is so common in households and why all family members are often treated at the same time.
Treatment is straightforward and highly effective, typically involving a single dose of medication repeated two weeks later to catch any worms that were still eggs during the first dose. Washing bedding and underwear in hot water on the morning treatment begins helps reduce the chance of reinfection from lingering eggs in the environment.