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Threadworms and Breastfeeding

Breastfeeding mothers may take mebendazole and continue to breastfeed as normal

Threadworms, also known as pinworms, are tiny parasitic worms that infect the large intestine of humans. Threadworms are a common type of worm infection in the UK, particularly in children under the age of 10. European estimates have suggested that 20 to 30% of pre-school and primary-school-aged children will have threadworm infestation. The worms are white and look like small pieces of thread.

Threadworms spread easily within childcare settings when children scratch their bottoms causing the eggs which have come out of the anus, to collect underneath fingernails. They can then be transferred into the mouth or substances like PlayDough! I know it is a yucky thought bit part of toddler life!

How threadworms spread

Threadworms spread when their eggs are swallowed. They lay eggs around the bottom (anus), which make it itchy. The eggs get stuck on fingers when scratching. They can then pass on to anything touched, including:

  • clothes
  • toys
  • toothbrushes
  • kitchen or bathroom surfaces
  • bedding
  • food
  • pets

Eggs can pass to other people when they touch these surfaces and then touch their mouth. They take around 2 weeks to hatch.

Once ingested, larvae emerge from the eggs and mature within 1–2 months into adults in the small intestine. The mature adult female worm migrates through the anus and lays thousands of eggs on the peri-anal skin (typically at night) causing itching. Adult threadworms survive for about 6 weeks and infection is maintained by swallowing fresh eggs.

Complications caused by threadworm include:

  • Lack of sleep (due to itching) with subsequent daytime irritability and difficulty in concentrating.
  • Bedwetting
  • Weight loss or loss of appetite.
  • Breakdown and soreness of the skin around the back passage

Treatment (BNF)

  • In adults, 100 mg mebendazole (Ovex ™ or Vermox ™) for 1 dose. If reinfection occurs, a second dose may be needed after 2 weeks.
  • In children, aged 6 months to 17 years, 100 mg for 1 dose, if reinfection occurs, a second dose may be needed after 2 weeks.


  • Amount present in milk too small to be harmful but manufacturer advises avoid (BNF).
  • Oral bioavailability 2-10%, highly plasma protein bound, half life 2.8-9 hours Considering the poor oral absorption and high protein binding, it is unlikely that mebendazole would be transmitted to the infant in clinically relevant concentrations (Hale Medications and Mothers Milk accessed April 2023)
  • Mebendazole is poorly excreted into breastmilk and poorly absorbed orally. Reports on the use of mebendazole during breastfeeding have found no adverse reactions in breastfed infants. (LactMed https://www.ncbi.nlm.nih.gov/books/NBK501340/ accessed April 2023)
  • Based on a low oral bioavailability, concentration in the infant’s plasma should be nil or low, except in premature and newborn infants with a increased intestinal absorption capacity. (Elactancia https://www.e-lactancia.org/breastfeeding/mebendazole/product/ accessed April 2023)

Breastfeeding mothers may take the mebendazole and continue to breastfeed as normal

Things to do to stop re-infection

  • wash hands and scrub under fingernails – particularly before eating, after using the toilet or changing nappies
  • encourage children to wash hands regularly
  • bathe or shower every morning
  • rinse toothbrushes before using them
  • keep fingernails short
  • wash sleepwear, sheets, towels and soft toys (at a hot temperature)
  • disinfect kitchen and bathroom surfaces
  • vacuum and dust with a damp cloth
  • make sure children wear underwear at night – change it in the morning

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