What Are Pinworms?

  • Jasmine Le Third Year (BSc) Microbiology Student (Graduating 2025)


Restless nights and constantly itching. Even seeing the presence of these common parasites can be disconcerting. Pinworms are one of the most frequently reported parasites of humans and the idea of you or your child having ‘worms’ can be justifiably unnerving.

However, this common infection can easily be treated with the right knowledge on how to prevent its spread and potential re-infection. Although having pinworms might be uncomfortable and concerning, it is very rarely serious if you recognise symptoms, seek medical help, and follow directions for treatment closely. 

Who’s at risk of pinworms?

Pinworms are present globally. Though, as this parasitic worm is better adapted to surviving in cooler temperatures, it is more abundant in temperate climates. In particular, it is the most commonly reported parasitic worm in the US, northern and western Europe.1,2

Anyone can contract pinworms. However, it is often reported in school children or individuals attending an institution (e.g. care centres or nurseries). Caregivers of individuals who are infected with pinworms are also at risk.1

What are pinworms?

Pinworms are a type of parasitic worm - specifically, they belong to a group of worms known as ‘nematodes’. The pinworm that infects humans is scientifically called Enterobius vermicularis or the ‘human pinworm’ as it only infects people. Other names such as ‘threadworm’ and ‘seatworm’ are also used.

The name ‘pinworm’ comes from the long, thin tail seen in females of this species. They spend their adult life inside the colon of their host. Adult worms are very small and thin, only a few millimetres in length. Males are smaller than females, though they are rarely seen.1

Pinworm life cycle

The pinworm life cycle begins with the eggs or ‘ova’. They start life being laid on the skin around a person’s anus after a female emerges during the night. Eggs may be transferred via a patient's hands after scratching this area or handling a surface contaminated with eggs.

The oxygen outside of the body rapidly allows the eggs to mature and become infectious after laying (around 4 - 6 hours).2 

When a person accidentally consumes these eggs, they pass into the start of the small intestine, where they hatch. The newly hatched pinworms then mature as they migrate to the end of the small intestine, where the adult pinworms mate.

Males die shortly after mating and don’t normally cause symptoms. Females pass to the large intestine, where they attach to the intestinal lining and absorb nutrients from digested food.

During this part of their life cycle, females develop their eggs inside their bodies. A single female can develop up to 11,000 eggs in as little as 1-2 months. However, the eggs don't mature until they are exposed to fresh air outside of the host’s body.

The female pinworms leave via the host’s anus and deposit eggs on the surrounding skin, referred to by doctors as the ‘perianal’ region. This process tends to cause intense itching in this area. The female dies at this point, but the eggs may easily spread onto other surfaces or the host's hands and, if accidentally consumed, will start the life cycle again. Rarely, eggs may hatch whilst still on the host and return to the host via the anus. This is known as retro-infection.

How do pinworm infections occur?

Pinworm infection easily spreads to new hosts who consume the eggs - known by medical professionals as the ‘faecal-oral route’. This is due to the sheer number of eggs a single female can produce, and how resilient the eggs are. Pinworm eggs can survive for 3 weeks on a surface and even resist household cleaning disinfectants or soaps.

Due to the egg's small size and the tendency of people to scratch when the pinworms emerge and cause itching - especially young children, the eggs easily get transferred onto hands. The eggs are particularly likely to get underneath fingernails but may also contaminate any surfaces such as clothing, bedding, food or even toilet seats.

The eggs may also become airborne and can be inhaled or swallowed - this is rarer but typically occurs when contaminated sheets or clothing are shaken.1,2

Signs and symptoms

The classic symptoms of pinworm infection are itching around the anus and genital areas caused by the movement of pinworm females as they lay eggs. This typically happens at night, causing restlessness and disturbed sleep. Though, pinworms may not cause any symptoms.1,2

Other potential symptoms and complications

Pinworm infection is not serious. Rarely, however, it may cause some complications. Scratching can sometimes break the skin, leaving small wounds open to bacterial infection, particularly in the area around the anus.

In a few cases, the pinworms may enter the vaginal opening and cause further irritation and vaginitis - a bacterial infection of the vagina.

Another symptom is a side-effect of insomnia, caused by intense itching throughout the night.   Additionally in small children, pinworms can cause a lack of nutrients due to the parasite absorbing them during digestion. This may be visible as teeth grinding, bed-wetting, weight loss or stomach ache. Any stomach ache may be accompanied by constipation or ‘tenesmus’ - the need to frequently go to the bathroom but unable to pass stool. However, this is a very rare symptom.

Very rarely, the presence of pinworms can cause intense inflammation as immune cells attack the source of irritation in the colon. This inflammation is called ‘eosinophilic colitis’ and may cause damage to the lining of the colon.1,2,3

Risk factors

The main risk factor for pinworms is exposure to people who are already infected. This means pinworm infection tends to occur when multiple people share the same household or attend the same institution - e.g. a care centre or school.1

Parasites are often associated with lower income levels and areas with poor sanitation. It is important to recognise that the risk of pinworm infection is not affected by economic status and is equally present in low- and high-income areas. Even impeccable hygiene standards don’t eliminate the risk of infection.3

The eggs survive best at low temperatures, preferring high humidity. Dry, warm conditions can kill the eggs and reduce the time they remain infectious on contaminated surfaces.2


Diagnosis of pinworms is usually done by directly observing the pinworms or their eggs. If the symptoms of nocturnal itching and restlessness are a cause to suspect pinworms, then self-diagnosis may be possible. The worms tend to emerge around 2-3 hours after falling asleep and may be observed on the skin around the anus at this time or on underwear worn to bed.

If worms cannot be seen, another method known as the ‘tape test’ may be recommended. This involves taking a piece of adhesive tape and placing it on the area around the anus before peeling away. The tape may pick up eggs present on the skin, and a doctor will inspect these under a microscope. Tape tests must be done immediately after waking, before washing or going to the toilet, as this may remove any eggs. Repeating the test over three days maximises the chances of finding eggs. Eggs may also be found by scraping under the fingernails.1

Treatment options

Pinworms is usually easily treated. The main difficulty is that re-infection can be a common problem if the medication isn’t properly administered.

You may be prescribed a general anti-parasitic drug such as mebendazole, pyrantel pamoate, or albendazole. Many of these drugs work by stopping worms from absorbing sugars (glucose) in the digested food passing through the intestines. One dose should be taken initially, with a second taken about 2 weeks later.

It is critical that everyone in a household or institution is treated and takes both doses at the same time.  Even one remaining, infected person could spread it back to every other contact.


Medications used for pinworm treatment typically may have some temporary side effects, such as headache or nausea, but are usually well-tolerated. Young children, under the age of 2, may not be prescribed these drugs.

Pregnant individuals may not be recommended to take medication unless there is a concern about the pregnancy. It will generally only be prescribed after the 3rd trimester. Breastfeeding is safe to continue with mebendazole, as only trace amounts have been detected in breast milk.1

A topical ointment to relieve itching may be provided.3


Pinworm infections are highly preventable with simple yet effective measures. By incorporating the following practices into daily life, the risk of pinworm infection and re-infection can be significantly reduced.


Thorough and regular handwashing, especially after using the bathroom and before meals, is crucial. Teach children the importance of personal hygiene, including proper handwashing techniques and the importance of keeping hands away from the mouth and face. Avoiding scratching or biting nails is very important, and cutting nails short can reduce the risk of spreading eggs.1

Cleaning and disinfecting living spaces: Regularly clean and disinfect living spaces, paying attention to frequently touched surfaces. While traditional antibacterial sprays or bleach may not be entirely effective, diligent cleaning practices can still reduce the risk of contamination.

Emphasise daily showering and changing underwear to minimise the likelihood of eggs lingering on clothing. Maintain regular laundry cycles, ensuring bedding and clothing are washed thoroughly. Avoid shaking bedding or clothes that may be contaminated.

Alongside treatment, these precautions are particularly important in controlling the spread of pinworms, especially when an outbreak is occurring in a shared institution such as a school or nursery.1,3


While pinworm infections can cause discomfort, they are easily manageable and preventable with appropriate knowledge and practices. Pinworms are common but not usually serious, with easily recognisable symptoms. By understanding how they spread and how to avoid re-infection, they can be quickly diagnosed and treated.


Can I catch pinworms by using a swimming pool?

Pinworms are not thought to easily spread through swimming pools. The chlorine won’t kill the eggs but will be so heavily diluted in the water that infection is unlikely.

It is important to avoid bathing young children together or sharing towels. Showers are preferable as this will rinse away any eggs.1

Can I catch pinworms from my pets?

Enterobius vermicularis is unique to humans. However, eggs may be carried in fur even if the pet isn’t infected.1,2


  1. Prevention, CDC-Centers for Disease Control and. CDC - Enterobiasis. 5 June 2023, Available from: https://www.cdc.gov/parasites/pinworm/index.html.
  2. Caldwell, J. P. ‘Pinworms (Enterobius Vermicularis)’. Canadian Family Physician, vol. 28, Feb. 1982, pp. 306–09. PubMed Central, Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2306321/.
  3. Cook, G. C. ‘Enterobius Vermicularis Infection.’ Gut, vol. 35, no. 9, Sept. 1994, pp. 1159–62. gut.bmj.com, Available from: https://doi.org/10.1136/gut.35.9.1159.
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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George Yates

BSc Zoology – University of Bangor, Wales

George is a researcher currently working in the medical diagnostics industry. His work is focused on infectious disease microbiology and molecular biology, and he also has several years of experience in the food safety, pharmaceutical and biotechnology industries.

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