Side effects of radiotherapy for anal cancer | Cancer Research UK
Cancer Research UK on Google+ Cancer Research UK on Facebook Cancer Research UK on Twitter

Side effects of radiotherapy for anal cancer

Men and women discussing anal cancer

Read about the side effects of radiotherapy for anal cancer.


A quick guide to what's on this page

Radiotherapy for anal cancer – side effects

Side effects of radiotherapy usually start during the course of treatment. They can carry on for a week or two after treatment has finished. 

Side effects can include

  • Tiredness
  • Sore skin around the anus and groin
  • Bladder irritation
  • Opening your bowels frequently
  • Feeling sick

Your doctor can prescribe painkillers to help with skin soreness. They can also give you medicines to stop you feeling sick, or to control diarrhoea. Your nurse can tell you how to care for sore or broken skin.

Drink plenty of water if you have bladder irritation, diarrhoea or are feeling sick. Wearing loose clothes and underwear helps with sore skin. You might also need a soft cushion to sit on.

Long term side effects

Some people get long term side effects from radiotherapy. These can start a few months or even a couple of years after treatment. They include frequent bowel movements and passing urine more often. Women may have dryness or shrinkage of the vagina and an early menopause. Men may have difficulty getting an erection. There are ways of controlling these effects.


CR PDF Icon You can view and print the quick guides for all the pages in the Treating anal cancer section.



Short term side effects

Short term side effects of radiotherapy usually start during the course of treatment. They can carry on for a week or two after treatment ends. These side effects can include the following.

Feeling tired

You may feel more tired as your treatment goes on. This is common with radiotherapy. It can be from travelling back and forth to hospital or because of the treatment itself.

Rest when you feel you need to. Daily, gentle exercise can be helpful.

Sore skin around the anus and groin

Radiotherapy can make the skin sore around the anus, genitals and groin. Nowadays radiographers use newer machines and treatment techniques. This means that skin problems happen less often than they used to. The skin around the anus is sensitive. It can get quite red and sore during your radiotherapy treatment. 

Your skin may also break down. This can make opening your bowels painful. Your doctor or nurse can prescribe painkillers to help until your skin heals up. You might need a soft cushion to sit on for a while. Wearing loose, comfortable underwear and clothing also helps during this time.

Your nurse can tell you how to care for your skin. Keeping the area clean is important, but rubbing while washing can make the soreness worse. You should only wash the area with plain water and simple soaps such as baby soap. Pat the skin dry with a soft towel. Or you can use a hairdryer on a cool setting. Don’t use perfumed or medicated soaps or other products. Discuss anything you'd like to use first with your specialist, radiotherapy nurse or radiographer.

Bladder irritation

The bladder is close to the bowel and rectum (back passage). Radiotherapy to the bowel often irritates the bladder. You might feel

  • You have cystitis (a bladder inflammation)
  • You want to pass urine all the time but when you go there isn’t much there
  • A burning pain when you do pass urine

Try to drink plenty of fluids. Many people find drinking cranberry juice can be helpful with bladder problems. If you take an anti clotting tablet called warfarin, check with your blood clinic first.

Bladder irritation usually settles down after the treatment is over. Let your doctor or nurse know if it continues. You may need to have a tube into your bladder (a urinary catheter) for a short time. You might also have an infection that needs treatment with antibiotics.

Opening your bowels frequently

This is quite common after radiotherapy to the anus. It happens because the radiotherapy causes irritation and inflammation of the anus and rectum. This means your rectum can’t hold your stools (faeces) as well as normal.

You may also have sore skin around the anus, which can make opening your bowels painful. Tell your doctor and nurse about any pain you have. They can make sure you have the most appropriate painkillers. 

Your doctor may also prescribe drugs to help reduce the irritation and inflammation. These can help your bowels to open less frequently. These include steroid enemas if the problem is severe. Irritation and inflammation usually settles down about 2 to 3 weeks after your treatment ends.

You may get diarrhoea, particularly if you are also having chemotherapy. You might need medicines to control this. Drinking plenty of fluids and having a low fibre diet may also help. Your radiographer or radiotherapy nurse can tell you about this. They may have leaflets about diet. A low fibre diet means 

  • Cutting out whole grain cereals and wholemeal bread
  • Not eating too many helpings of fibrous vegetables, fruit or fruit juice

Feeling sick

Tell your doctor or nurse if you feel sick. They can give you medicines to stop you feeling sick.

You might not want to eat or drink much if you are feeling sick. It is important though to drink plenty of fluids if you can. If you are having trouble eating, try having high calorie drinks. You can get these on prescription, or buy them from your chemist.


Possible long term radiotherapy side effects

Radiotherapy can cause short term side effects while you have treatment. Some people also get long term side effects. Your doctors will try their best to make sure you have as few side effects as possible. But some people are more sensitive than others to radiation. 

Long term side effects are more likely with higher doses of radiation. Long term effects are unlikely with a short course of radiotherapy to treat symptoms.

The long term effects can begin from a few months to a couple of years after you finish your course of treatment. The long term side effects of radiotherapy to the bowel or rectum may include

  • Frequent bowel movements
  • Passing urine more often, as your bladder can become hardened and may shrink 
  • Difficulty passing urine because the tube from the bladder to outside your body narrows
  • Extra blood vessels can grow in your bladder and rectum, which may cause blood in your urine and stools
  • Dryness and shrinkage of your vagina and discomfort during sex –using vaginal dilators after treatment can minimise this
  • Difficulty getting an erection
  • Loss of fertility for men and women
  • Early menopause
  • Weak muscles in the anus, leading to incontinence
  • Chronic diarrhoea and weight loss
  • Damage to the bones of your hip causing hip pain

Talk to your doctor if you think you have developed any of these effects. It may be that your symptoms are due to something else, such as a bowel or bladder infection. If you do have a side effect, your doctor or nurse can help to manage your symptoms.

Regular pelvic floor exercises can help with side effects affecting your bladder or bowel. Your nurse, physiotherapist or continence advisor can give you information about these.

If you smoke, it is a good idea to stop before you start radiotherapy treatment. It can help to reduce the side effects caused by treatment, as well as improving your general health.

Stopping smoking can be difficult, particularly when you are going through a stressful time. Talk to your doctor or nurse about support for stopping smoking.


More about radiotherapy side effects

Find out about

Stomach and abdominal side effects

Sex and anal cancer

Sex and cancer for women

Coping with eating problems

Coping with tiredness

Pelvic floor exercises

For general information and support

Contact the Cancer Research UK nurses on freephone 0808 800 4040 (Open 9am to 5pm, Monday to Friday)

Share experiences on our online forum – Cancer Chat

Rate this page:
Submit rating


Rated 5 out of 5 based on 37 votes
Rate this page
Rate this page for no comments box
Please enter feedback to continue submitting
Send feedback
Question about cancer? Contact our information nurse team

No Error

Updated: 7 June 2016