What is an anal abscess and why does it occur?

An anal or rectal abscess is a condition where an infected cavity filled with pus develops near the anus. It is extremely painful and can cause fatigue, fever and rectal discharge. Most patients experience perianal abscess, a painful burning sensation near the anus. About 50% of patients with an anal abscess will develop a complication known as a fistula, a small tunnel which abnormally connects the site of the abscess and the skin of the anus. 

This is a relatively high percentage, but not surprising at all. The prevalence of anal abscesses in general are underestimated or unknown since most patients do not seek medical attention. Either that or their symptoms are dismissed as symptomatic haemorrhoids. I believe raising awareness plays a huge part in reducing the percentage of cases of any condition. From the interactions with my patients, I can only assume that anal abscesses are quite unfamiliar among Singaporeans. Let me explain more about this condition further.

How does an anal abscess form, and what causes an anal abscess?

An anal abscess is usually caused by: 

  • A tear in the anal canal that becomes infected 
  • Sexually transmitted infections 
  • Blocked anal glands 

Certainly, multiple factors can increase a person’s risk of developing an anal abscess. These include conditions that cause an increase in intra-abdominal pressure, such as: 

  • Chronic constipation and diarrhoea 
  • Persistent strained bowel movements 
  • Pregnancy 
  • Obesity 
  • Intra-abdominal or pelvic tumour 
  • Crohn’s disease, an inflammatory bowel disease that causes the body to attack healthy tissue

Other risk factors include: 

  • Diabetes 
  • Undergoing chemotherapy 
  • HIV or AIDS which compromises the immune system 
  • Anal sex 
  • A diet low in fibre 

Additionally, children who have a history of tears in the anal sphincter are at a higher risk of developing anal abscesses later on in life. Tears in the anal sphincter are usually caused by constipation. Also, changing their diapers frequently with proper cleaning can prevent perianal abscesses. So parents might want to keep this in mind. 

Usually, patients complain of severe pain in the anal area which has been present for several days. This pain is due to an acute infection of the anal glands which are not draining properly through the anal crypts. When this occurs, the anal glands will form an abscess or collection of pus which can spread along the perianal space. The perianal space is located around the anus and fat of the buttock.

What are the symptoms of an anal abscess?

One of the most common and obvious symptoms of an anal abscess is a throbbing and constant pain and swelling in the anal area. This pain is intensified during bowel movements. Other signs to look out for are constipation, rectal discharge, skin irritation around the anus, fever and fatigue. 

Some patients may be able to feel a swollen lump at the rim of the anus and experience difficulty urinating too. Those with inflammatory bowel diseases may get anal abscesses deeper in the rectum, which results in pain in the abdominal area. 

For toddlers and young children, there usually aren’t many symptoms apart from a lump around the anal area and signs of discomfort which will be reflected in the child’s behaviour.

Diagnosing an anal abscess

Anal abscesses are usually diagnosed through a bedside physical exam where the anus is checked for characteristic nodules. Occasionally, if there are no visible signs of the abscess around the anus, I use an endoscope to look inside the anal canal and lower rectum. This is because the abscess may be deeper and a physical exam will not cut it. In some cases, an MRI or ultrasound may also be done. 

For patients whom I suspect Crohn’s disease is a contributing factor, I may do a blood test or colonoscopy to examine the colon.

Treating an anal abscess

Patients often sit and wait, hoping the abscess will go away by its own. But anal abscesses require treatment. This is done by draining the pus from the infected area and is performed in the doctor’s office as a day surgery. You should be able to feel some relief afterwards. 

For extremely large anal abscesses or fistulas, surgery may be required. The surgery involves cutting away a small portion of the anal sphincter muscle to open and convert the tunnel into a groove which will heal from outward. 

After treatment, I suggest taking warm showers and sitting in warm water to reduce swelling and allow for more drainage from the abscess.

Prevention is key

There isn’t any surefire way to prevent an anal abscess since this condition can happen to anyone, but there are a few ways to protect yourself, such as: 

  • Using condoms during sexual intercourse — especially during anal sex. Protecting yourself against STIs go a long way as STIs may cause anal abscesses 
  • Practice good hygiene in the anal area


  1. Sahnan, K., Adegbola, S. O., Tozer, P. J., Watfah, J., & Phillips, R. K. (2017). Perianal abscess. BMJ (Clinical research ed.), 356, j475. https://doi.org/10.1136/bmj.j475
  2. Pigot F. (2015). Treatment of anal fistula and abscess. Journal of visceral surgery, 152(2 Suppl), S23–S29. https://doi.org/10.1016/j.jviscsurg.2014.07.008

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