What Causes Anal Itching?

Patient Presentation
A 7-year-old male came to clinic with a history of 2 days of significant anal itching. It was worse at night and he had seen “white stuff in my poop.” He and his mother denied any general skin problems but she noted, “he’s not always the best with cleaning himself after using the restroom.” There was no diarrhea, constipation or encopresis, changes in soaps, lotions, detergents, or other skin products. His diet was unchanged. He did attend a before and after school childcare program that had recently visited a local farm. There were no known ill contacts. The past medical history was non-contributory.

The pertinent physical exam revealed a healthy appearing boy with normal growth parameters and vital signs. His examination was normal except for general irritation around his anus and excoriation marks. No specific track or burrows were seen.

The diagnosis of probable pinworms was made. The patient was treated empirically with anti-helminths which his mother said had worked when he returned for his next health supervision visit.

Pinworms are caused by the parasite Enterobius vermicularis. Humans are the only known reservoir and are infected by fecal-oral transmission of eggs or indirectly such as through contaminated clothing or bedding. It is commonly seen in children and can easily pass to family members, plus people can become easily reinfected. The incubation period is usually 1-2 months and eggs can survive outside humans for 2-3 weeks. Adult worms migrate at night from the anus to the perianal skin and vulvar areas causing anal or vulvar itching. The itching can cause sleep problems and scratching can cause secondary bacterial infection. The worms can exist in alternative locations such as the vagina, Bartholins glands and the urethra.

Diagnosis is by direct visualization of the adult worms about 2-3 hours after sleep or by the “scotch-tape test” where upon wakening the patient has clear cellophane tape applied to the perianal skin. The tape is then reviewed under a microscope to identify the adult worms. In many cases pinworms are treated presumptively because of the difficulty of obtaining specimens. Treatment is by antihelminthic agents such as mebendazole, albendazole, and pyrantel pamoate. Handwashing and laundering items in hot water helps to decrease transmission.

As pain and itch nerves travel together it can be difficult for patients to be able to distinguish between the two different sensations. Patients may complain of general genital area pain or specific anal pain and not pruritis. Significant pruritis can also cause pain too.

In younger children, soiling and hygiene issues along with skin conditions probably are the most common causes of anal pain and/or itch, but pinworms are quite common in this population and should be suspected.

Learning Point
Pruritis ani is “…an itch localised to the anus and peri-anal skin without a rash.” Peri-anal dermatosis is different and is caused by inflammatory diseases affected the anal area occurring with a rash. Given that patients often present with excoriation it can be difficult with some causes to tell these apart.

Causes of pruritis ani include:

  • Infection
    • Parasites – pinworms, scabies, swimmer’s itch
    • Bacterial – Streptococcus, Staphlococcus
    • Fungal – candida
    • Viral – pox and others
    • Sexually transmitted infections
  • Skin
    • Dermatitis – contact, atopic
    • Hidradenitis suppurative
    • Lichen sclerosis et atrophicus
    • Paget disease
    • Psoriasis
  • Soiling and hygiene
    • Encopresis
    • Diarrhea
    • Incontinence
    • Intertrigo
    • Hygiene products and medication – soaps, detergents, creams
    • Sweating
  • Anorectal problems
    • Anatomic abnormalities – rectal prolapse, hemorrhoid prolapse
    • Abscess
    • Fissures
    • Fistula
  • Diet
    • Acid containing products – citrus fruits, tomatoes
    • Beer
    • Caffeine containing products – chocolate, cola, coffee, tea
    • Milk
  • Systemic
    • Cancer – anal, rectal, colon, leukemia
    • Diabetes
    • Hepatic problem
    • Thyroid problems
  • Other
    • Drugs – chemotherapy
    • Psychological

Questions for Further Discussion
1. How often do you see parasites in your practice and what kinds?
2. How do you treat scabies?
3. What would be indications for consultation with a gastroenterologist for pruritis ani?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for these topics: Anal Disorders and Pinworms.

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Stermer E, Sukhotnic I, Shaoul R. Pruritus ani: an approach to an itching condition. J Pediatr Gastroenterol Nutr. 2009;48(5):513-516. doi:10.1097/MPG.0b013e31818080c0

Abu-Asi MJ, White IR, McFadden JP, White JML. Patch testing is clinically important for patients with peri-anal dermatoses and pruritus ani. Contact Dermatitis. 2016;74(5):298-300. doi:10.1111/cod.12514

Ng NBH, Lin JB. Pruritus ani in a school age boy. BMJ. 2022;376:e067817. doi:10.1136/bmj-2021-067817

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa