What causes anal (rectal) discharge?

Anal discharge, also known as rectal discharge, refers to the release of fluids, usually pus, mucus or blood, from your back passage (anus). Your anus is the opening at the end of your rectum (the last section of your large intestine) through which you pass your stools. 

Here, we’ll look at eight common causes of anal discharge. 

1. Sexually transmitted infections (STIs)

STIs that cause anal discharge usually occur due to having anal sex; however, in some cases, an STI that affects your genitals can spread to your anus. Common STIs that can cause anal discharge include chlamydia, gonorrhoea, herpes and syphilis.

You may notice mucus or pus on your underwear or on your stools. Other symptoms that can occur alongside anal discharge include an itchy anus, blisters around your anus, pain around or anus and anal pain when opening your bowels.

2. Piles

Also known as haemorrhoids, piles cause swellings to develop inside your rectum and/or around your anus. Not all piles cause symptoms; however, when piles do cause symptoms, this can include blood and mucus leaking from your anus, especially after opening your bowels. Other symptoms include anal pain, a sore and/or itchy anus, and constipation.

Around half of all adults in the UK will develop piles at some point in their life. One of the most common causes is chronic (long-term) constipation, where frequent straining to pass stools increases the pressure in blood vessels in the anus, which leads to tissue swelling to form a lump. Other causes of piles include chronic diarrhoea, inflammatory bowel disease, a persistent cough and frequent heavy lifting.

3. Irritable bowel syndrome (IBS)

Up to one in five adults in the UK has IBS, which can lead to anal discharge in the form of mucus. Other symptoms of IBS include abdominal pain, abdominal bloating, cramps, constipation, diarrhoea and flatulence. 

The exact cause of IBS isn’t clear; however, symptoms often occur in response to stress, certain foods and/or large meals. IBS also tends to run in families and may involve nerves that supply your gut being oversensitive and/or food moving too quickly or slowly through your gut. 

4. Inflammatory bowel disease

Around one in every 120 adults in the UK has inflammatory bowel disease, which refers to chronic inflammation of the large intestine. It includes both Crohn’s disease and ulcerative colitis and can cause anal discharge in the form of mucus, which may be bloody. 

Other symptoms of inflammatory bowel disease include abdominal pain, frequent diarrhoea, fatigue and unintentional weight loss. 

It isn’t clear what causes inflammatory bowel disease although your genetics, environmental factors and an abnormal reaction of your immune system can all trigger Crohn’s disease or ulcerative colitis. 

5. Rectal prolapse

A rectal prolapse occurs when your rectum bulges out of your anus. It may bulge out all the time or only when you open your bowels, after which it slips back into place. It is caused by weakening of the muscles around your rectum. This leads to the leakage of stools from your anus. 

The most common causes of a rectal prolapse include ageing, pregnancy and childbirth, which can all weaken the pelvic floor muscles that support your rectum and bladder.

6. Anal fistula 

This refers to a tunnel (or network of tunnels) that develops between your anus and rectum. It can lead to blood and pus leaking from your anus, especially after opening your bowels. Other symptoms include anal pain, an itchy anus, bowel incontinence and red, irritated skin around your anus. 

An anal fistula is caused by an infection around your anus that causes pus to collect in the tissue around your anus. After the pus drains, a tunnel — fistula — is left behind.

Anal fistulas are most often caused by anal abscesses, with risk factors including chronic bowel conditions, such as Crohn’s disease and diverticulitis.

7. Anal abscess

Also known as a perianal abscess, it occurs when a gland in your anus becomes blocked. This leads to the gland becoming infected with bacteria, which then causes a pus-filled structure (abscess) to form under the skin around your anus.

An anal abscess can cause blood and pus to leak from your anus, as well as anal pain that is worse when sitting down or opening your bowels. Other symptoms include redness and swelling around your anus and constipation. 

Your risk of developing an anal abscess is higher if you have a weakened immune system or an STI, engage in anal sex or have inflammatory bowel disease, diabetes, diverticulitis or pelvic inflammatory disease. 

8. Proctitis

This refers to inflammation of the lining of your rectum and can cause mucus, pus or blood to leak from your anus. Other symptoms include anal pain, pain when opening your bowels, a full feeling in your anus even after opening your bowels, diarrhoea and a constant or frequent feeling that you need to open your bowels. 

Proctitis can be caused by inflammatory bowel disease, STIs, gastrointestinal infections (eg food poisoning with Campylobacter, Salmonella or Shigella) and radiotherapy targeting cancer in an area near your rectum.

When to see a doctor

If you have noticed discharge from your anus, particularly if this is a new symptom, it is important to see your GP to have it investigated. 

Your doctor will ask you about your symptoms and medical history, and may perform a physical examination of your anus and rectum. If needed, they may refer you for further tests, such as imaging tests and blood tests. This will help them identify the underlying cause of your anal discharge and rule out anal cancer. 

Although anal cancer is a rare type of cancer — accounting for less than one percent of all cancer cases in the UK — and consequently is rarely the cause of anal discharge, its symptoms overlap with those of common conditions such as piles and IBS. This makes it important to rule out anal cancer as the cause of your symptoms. 

Anal discharge caused by anal cancer can be in the form of mucus and/or blood. Other symptoms include anal pain, an itchy anus, bowel incontinence, loose stools, blood in your stools, opening your bowels more often and/or frequently feeling that you need to open your bowels, and the sensation that there is a lump in your anus.