Side effects of radiotherapy

Radiotherapy damages cancer cells but can also affect normal cells close by. This is what causes any side effects that you get.  

Radiotherapy machine

You usually get side effects in the part of your body that is being treated. You may also have some general side effects, such as feeling tired. Side effects usually build up during treatment. After treatment finishes, it can take a week or two before side effects start getting better. Most of them usually go away gradually after that.  

Sometimes, side effects take longer to improve. Or sometimes new side effects develop months or years after radiotherapy. These are called late effects. Your specialist doctor and nurse will explain the risk of any late effects.  

We have listed some possible side effects of radiotherapy below. 

Always tell your radiotherapy team about any side effects that you have or if they get worse. Your team can usually do something to improve the side effects, or they can give you more advice.  

Before treatment starts

Your doctor, nurse or radiographer will tell you what to expect. They will give you advice on what you can do to manage side effects.  

They will also give you advice on preparing for treatment. For example, if you are having radiotherapy to the head and neck, you may need to have a dental check before treatment starts.  

Your doctor will explain if treatment might affect being able to get pregnant or make someone pregnant (your fertility). Before treatment starts you can see a specialist about possible ways of preserving your fertility.  

Radiotherapy is harmful to an unborn baby, so it is important to prevent you or a partner getting pregnant. If you are having sex during treatment, your doctor or nurse will advise you to use contraception. They can advise you on how long you should continue to use contraception for.  

If you smoke, it is important to try to stop. Stopping smoking can make radiotherapy work better. It also reduces the side effects of treatment. It can be difficult to stop, but there’s lots of support to help you. Your doctor or nurse will give you advice. There are also NHS services to help people stop smoking. 

General side effects of radiotherapy


This is a common side effect and probably the main one you will notice. You usually get more tired as treatment goes on. Having other treatments (such as surgery or chemotherapy) or travelling to the hospital every day can also make you feel more tired (fatigued).  

It can help to: 

  • try not to do too much 
  • get plenty of rest  
  • do some gentle exercise, such as short walks – this will help give you more energy.  

After treatment finishes, you may continue to feel tired for a few weeks or months. If it does not get better, let your doctor or nurse know.  

If you feel up to it, there is no reason you can’t still go out with your friends. It may help to tell them you might have to cancel plans at short notice if you are too tired. You can also keep up with friends through social media or texts so you still feel involved.  

If you are studying, you will probably need some time off from school or university during your treatment. But you may be able to have some home schooling. Try not to worry about catching up. Schools and universities are used to helping students who have been unwell. They can set up any extra help you might need.  

Skin changes in the treated area  

In the area of your body that is being treated, the skin may feel dry and itchy after a few days. Depending on the colour of your skin, it may redden or become darker.  

Your radiographer or nurse will give you advice on how to look after your skin. If it becomes sore, flaky, or broken in areas, tell them straight away. If you do get a skin reaction, it should get better within four weeks of treatment finishing.  

Here are some skin care tips:  

  • Try to wear loose cotton clothing in the area that is treated. It will be less likely to irritate your skin. 
  • Wash your skin gently with mild soap (or aqueous cream) and water. Rinse the soap or cream off and pat your skin dry. 
  • Use unperfumed moisturiser on your skin every day. You can ask your radiographer about this.  
  • If your underarm is in the area that’s being treated use your normal deodorant, unless the skin is broken. 
  • Try not to shave the area being treated. If you feel you have to shave, use an electric shaver.  
  • Do not expose the area to sunshine. Protect your skin from strong sunlight for at least a year after treatment finishes. Use sun cream with a high sun protection factor (SPF) of at least 30.  

Eating difficulties  

Sometimes, you may not want to eat. Radiotherapy may cause side effects that make eating difficult. For example, radiotherapy close to the tummy or pelvis can make you feel sick. Radiotherapy to the head and neck area may make it difficult to swallow certain foods. Always tell your radiotherapy team if you have any eating difficulties or worries about your weight.  

Having small regular snacks throughout the day rather than three main meals is often easier. A dietitian can give you advice on foods or supplements you can add to your diet. Your doctor can prescribe medicines to control sickness or to help if you cannot swallow because of pain. 

Side effects of radiotherapy to your tummy or pelvis

Radiotherapy given close to your tummy or pelvis (the area between your hips) may cause different side effects.  

Feeling sick 

You may feel sick. Your doctor will prescribe anti-sickness drugs for you. These usually control any sickness you have. Tell your nurse or doctor if they do not, as there are different ones they can try. Any sickness goes away when your radiotherapy finishes.  


Radiotherapy to your pelvis may cause tummy cramps and diarrhoea. Your doctor will prescribe anti-diarrhoea tablets to take regularly until it settles down. It is important to drink plenty of fluids when you have diarrhoea. Your radiographer or nurse will give you advice on any foods you may need to avoid until the diarrhoea stops.  

Bladder irritation  

Radiotherapy to the pelvis can make you feel uncomfortable or sore when you wee (pass urine). It can also make you feel like you need to wee more often than usual. Let your doctor or nurse know if this happens or if your symptoms get worse. Your doctor can prescribe drugs to ease these symptoms and check for any urine infection.  

Try to drink 2 to 3 litres of fluids each day. Concentrated urine can irritate the bladder and make your symptoms worse, and drinking more fluids reduces this. Avoid drinks that can irritate the bladder. These include drinks with caffeine in them (tea, coffee, hot chocolate, cola), alcohol, fizzy drinks, acidic drinks (orange and grapefruit juice) and drinks with artificial sweeteners (diet or light drinks).  

Hair loss 

Radiotherapy to the pelvis will cause you to lose your pubic hair. It will usually grow back a few months after radiotherapy finishes.  

Side effects of radiotherapy to your chest

You might find it difficult to swallow, have a cough or feel breathless. Eating soft foods will make it easier to swallow. The radiotherapy team will give you advice on the kind of foods to eat. Your doctor can prescribe painkillers to make it more comfortable. If you have a cough or feel breathless, always let your doctor or nurse know.  

Side effects of radiotherapy to your head and neck

Your mouth and throat may become sore and you may have difficulty swallowing. Try to follow the advice from your radiographer or nurse about taking care of your mouth and keeping it clean. Your doctor can prescribe liquid painkillers. Your radiotherapy team will give you advice on foods to eat that make swallowing easier. Once your course of radiotherapy has finished, your mouth will gradually heal. Most people get back to eating normally after a few weeks.  

Radiotherapy to the head and neck may stop you making enough saliva. This means your mouth gets dry. Taking regular small sips of water can help. Your doctor can prescribe mouthwashes, lozenges, artificial saliva sprays or gels to help. Saliva washes your teeth and protects them from decay. 

Side effects of radiotherapy to the brain

Radiotherapy to the brain can cause different side effects. Common side effects include tiredness, itchy sore skin on your scalp, hair loss and headaches. Tell your doctor if you have headaches or feel sick. They can prescribe painkillers, steroids, or anti-sickness drugs to help. The side effects will usually improve gradually after treatment is over. 

Hair loss 

You will lose the hair in the treated area. You may also lose some hair on the opposite side of your head where the rays come out. The radiotherapy staff will show you where your hair is likely to fall out. They will give you advice on looking after the skin on your scalp. Your hair usually grows back within 2 to 3 months of finishing treatment. Sometimes, it grows back a slightly different colour or texture than before.  

Depending on the dose of radiotherapy, the hair might grow back thinner. Or sometimes there may be patches where the hair doesn’t grow back at all.  


Tiredness is a common side effect. Try to balance getting plenty of rest with doing some gentle activity, like short walks. This can help give you more energy. Tiredness can sometimes take months to improve.  

Some weeks after treatment, you may feel extremely tired, as if you want to sleep all the time (called somnolence). Tell your doctor or nurse if you feel like this.  

Sometimes side effects get worse after treatment but this is temporary. Let your doctor know if this happens. It usually gets better by itself over the following weeks.  

Late effects of radiotherapy

Radiotherapy can help to cure cancer. But it can sometimes cause side effects months or years later. These are called late effects or long-term side effects. Newer ways of giving radiotherapy help to reduce the chances of developing late effects.  

Late effects depend on where the treated area is and the dose of radiotherapy you had. Your specialist doctor or nurse will talk to you about any risk of late effects. After radiotherapy, you will have regular check-ups, usually for years. So, any problems linked to your treatment can usually be picked up and managed or treated early.  

A possible late effect of radiotherapy to the pelvis, or sometimes to the brain, is that it might affect your fertility. Fertility means being able to get pregnant or make someone pregnant. Your specialist doctor and nurse will talk to you about this. You can ask about possible ways of preserving your fertility before treatment starts. 

Another important late effect is the risk of getting another cancer in the treated area. The thought of this can be scary. But it is important to remember that this is rare. It can help to talk this over with your doctor or nurse. They will advise you to have any new symptoms or lumps checked by your specialist team or GP.  

Your specialist doctor or nurse can explain what you can do to help reduce the risk of certain late effects. This usually includes making healthy lifestyle choices such as not smoking, protecting your skin from the sun, keeping physically active and eating healthily.  

This can be a lot of information to take in at the start of your treatment. You can ask more questions when you go back for check-ups. 

Find out more about the possible late effects of radiotherapy in our section on late effects.