Threadworms in Adults: Symptoms, Treatment and UK Management

Threadworms, also known as pinworms (Enterobius vermicularis), are tiny, white, parasitic worms that live in the human colon and rectum. While often associated with primary school children, they are highly contagious and frequently affect adults within the same household. According to NHS guidance, they do not usually cause serious health problems, but they can be distressing and uncomfortable.

The worms look like small pieces of white thread, measuring roughly 5mm to 13mm in length. They survive by consuming nutrients in the gut and emerge from the anus at night to lay thousands of microscopic eggs on the surrounding skin. This process triggers the characteristic itching that leads to further spread.

In many adults, a threadworm infestation may be asymptomatic. However, the most common sign is pruritus ani—intense itching around the anus or vagina. This itching is typically most severe at night because the female worms are most active when the body is at rest.

• Visible worms: You may notice thin, white worms in your stools or on your underwear at night.
• Disturbed sleep: The persistent itching can lead to insomnia or irritability.
• Secondary skin irritation: Constant scratching can lead to redness, soreness, or even bacterial infections around the perianal area.
• Vaginal symptoms: In women, the worms can sometimes migrate to the vaginal area, causing itching or discharge.

Threadworm eggs are incredibly resilient and can survive for up to three weeks outside the human body. Transmission occurs via the 'faecal-oral' route. When an infected person scratches their bottom, eggs become lodged under the fingernails. These eggs are then transferred to surfaces, food, or directly to other people.

Common vectors for transmission in a UK household include door handles, bathroom taps, television remotes, and shared towels. Once someone else touches these surfaces and then touches their mouth, the eggs are swallowed, hatch in the intestine, and the cycle begins again. This is why NICE clinical knowledge summaries emphasise that the whole household must be treated simultaneously, regardless of whether every member has symptoms.

The frontline treatment for threadworms in the UK is a medication called Mebendazole (often sold under the brand name Ovex). It works by preventing the worms from absorbing sugar, which causes them to die within a few days. It is available over-the-counter at pharmacies or via prescription.

The Hygiene Method

Medication kills the worms but does not kill the eggs already present in the environment. Therefore, strict hygiene for two weeks is essential to prevent reinfection:

• Wash all bedding and towels: Use a hot wash (at least 60°C) on the first day of treatment.
• Damp dusting: Use a damp cloth to wipe down surfaces rather than dry dusting, which can flick eggs into the air.
• Keep nails short: This reduces the space where eggs can hide.
• Morning showers: Wash the anal area thoroughly every morning to remove eggs laid overnight.
• Avoid sharing towels: Ensure every family member uses their own flannel and towel.

While many cases can be managed with pharmacy products, there are times when professional medical advice is necessary. If you are struggling to clear an infestation despite following hygiene protocols, or if you are pregnant or breastfeeding, you should speak to a GP online.

An online doctor can provide a consultation to confirm the diagnosis and discuss alternative treatment pathways. In the UK, Mebendazole is usually not recommended for children under two years old or during pregnancy (especially the first trimester). A GP can advise on the 'hygiene only' method or prescribe suitable alternatives. Furthermore, if the itching is accompanied by severe abdominal pain or weight loss, a clinical review is required to rule out other digestive concerns.

Recurrence is common in the UK, particularly in households with young children. To stop threadworms from coming back, maintain a high standard of hand hygiene. Always wash hands thoroughly after using the toilet and before preparing or eating food. Scrubbing under the nails with a nail brush is particularly effective. Encourage children to avoid biting their nails or sucking their thumbs, as these behaviours are primary drivers of reinfection.