Side effects of radiotherapy

Radiotherapy for anal cancer can cause side effects. Some possible side effects are:

  • tiredness
  • effects on the skin
  • bladder changes
  • bowel changes
  • feeling sick
  • hair loss.

Many side effects can be managed successfully and most will begin to get better a few weeks after treatment ends.

Some people may have side effects that last for longer, or develop a while after they have finished their treatment. These are called long-term or late effects.

Your cancer specialist, specialist nurse or radiographer will explain the most likely side effects in your situation. Always tell them about any new symptoms. They will be able to suggest ways of managing them and tell you about treatments that can help.

Possible side effects of radiotherapy during treatment

You may develop side effects during your treatment. Side effects build up slowly when you start treatment. They usually disappear gradually over a few weeks or months after treatment finishes. Your doctor, nurse or radiographer will discuss this with you so you know what to expect. Let them know about any side effects you have during or after treatment. There are often things they can do to help.

Side effects caused by smoking

The side effects of radiotherapy are made worse by smoking. Smoking will also make your treatment less effective. Your cancer doctor or nurse will advise you to try to stop smoking. They can give you support and advice.

We have more information about giving up smoking.


Radiotherapy can make you feel very tired (fatigue). Try to get as much rest as you can, especially if you have to travel a long way for treatment. Balance this with some physical activity, such as short walks, which will give your more energy.

Diarrhoea and passing wind

Radiotherapy is likely to cause changes in how your bowel works. This can cause problems such as diarrhoea or passing more wind than usual. Your doctor can prescribe medicines to help.

Your nurse or radiographer may give you advice about avoiding certain foods. Or a dietitian at the hospital can give you advice about this. We have more information about eating problems and cancer, including coping with diarrhoea and wind.


You may experience a stinging sensation when you open your bowels. Your doctor can prescribe local anaesthetic creams to help with this. Tell your doctor or nurse if you have any pain.

Skin reaction

It’s likely that your skin will be sore in the area being treated.

This usually happens 2 to 3 weeks after treatment starts. You may have soreness around the anus and in the groin. Men may also have soreness in the scrotum. Women may also have soreness in the vulva. If you have IMRT, your doctor may be able to avoid these areas. This means that skin reactions are usually milder. 

The radiographer or nurse will check the area and tell you how to look after your skin. It’s important to follow the advice they give you and only use products they recommend.

Sometimes the skin may become blistered and sore, which can be painful. Your doctor can prescribe painkillers, creams and dressings to help with this. The skin reaction may get worse towards the end of treatment and for up to 6 weeks afterwards. It usually heals quickly after that.

If your skin reaction makes passing urine painful, your doctor may suggest you have a fine tube (catheter) put into your bladder to drain the urine. They will remove this once your skin has healed. 

Inflammation of the bladder (cystitis)

Radiotherapy to the anal area may cause inflammation of the lining of the bladder. This can make you feel you want to pass urine more often. It also gives you a burning sensation when you pass urine.

It helps to drink plenty of water and other fluids to make your urine less concentrated. Your doctor can prescribe medicine to make passing urine more comfortable.

Feeling sick

Some people may feel sick (nauseous) during treatment. This is usually mild, and anti-sickness drugs (anti-emetics) can usually control it.

If you don’t feel like eating, you can replace meals with nutritious, high-calorie drinks. These are available from most chemists and your doctor can also prescribe them. It’s important to try to drink plenty of fluids.

Hair loss

Most people lose their pubic hair. It should grow back after your treatment finishes, although the hair loss may be permanent.

The hospital will give you drugs for the nausea and diarrhoea. They will also probably give you some cream for the inevitable sore bum.


Possible late effects of radiotherapy

Some people may still have side effects months after treatment ends. Or they may develop new side effects months or years later. These are called long-term side effects or late effects. Newer ways of giving radiotherapy aim to reduce the risk of getting late effects.

There is slightly more risk of developing late effects when you have radiotherapy and chemotherapy together (chemoradiation). Your doctor or nurse will talk to you about this.

Bowel changes

You may have loose stools, or more frequent bowel movements than before. Or you may feel the need to rush to the toilet to urgently move your bowels. Some people may find the anus leaks a little (incontinence), for example when they pass wind.

For most people, the change is not severe. It can usually be easily managed with changes to your diet. Always tell your doctor if you have any of these problems. Some people may need to take medication. We have more advice about diet after surgery.


Radiotherapy to the pelvic area usually causes infertility (the loss of the ability to have children) in both men and women.

If you are concerned about the risk of becoming infertile, it is important to discuss this with your specialist before starting treatment. We have more information about treatment and fertility.

Vaginal dryness and narrowing

Women may develop dryness and narrowing of the vagina.

Your specialist nurse may advise you to use a vaginal dilator. Dilators are tampon-shaped plastic tubes of different sizes, which you use with a lubricant. This helps keep the vaginal walls open and supple.

There are different creams, gels and lubricants that can help improve vaginal dryness. Your doctor or specialist nurse can give you more information about this.


For women who have not been through the menopause, pelvic radiotherapy usually causes an early menopause.

This can cause hot flushes and sweats, vaginal dryness and other symptoms of menopause. Your doctor or nurse can give you advice on managing menopausal symptoms. You can ask them about taking HRT (hormone replacement therapy).

Erection difficulties

Men may become unable to have an erection (erectile dysfunction – ED) after treatment. If this is a problem, talk to your doctor or specialist nurse. Treatment with drugs such as sildenafil (Viagra®) can help some men get and maintain an erection. If you can’t take these drugs, other methods may help.

We have more information about sexuality and cancer for men.

Back to Radiotherapy explained

Radiotherapy for anal cancer

Radiotherapy uses high-energy rays to kill cancer cells. You usually have it along with chemotherapy for anal cancer.

Before your radiotherapy

Before you start radiotherapy, your team will explain what your treatment involves and how it may affect you.

Your radiotherapy team

You will meet many different specialists from your radiotherapy team. You may see them before, during and after radiotherapy treatment.

After your radiotherapy

It can take time to recover from radiotherapy. Support is there if you have any problems.