Side effects

Radiotherapy can cause side effects, although many of these can be treated or prevented and most will pass after the treatment stops.

It's difficult to predict what side effects you'll get.

Side effects vary from person to person and depend on things such as the part of your body being treated and the type of radiotherapy you have. Ask your care team about the side effects you might get.


In some people, radiotherapy can make the skin sore and red (similar to sunburn), darker than normal or dry and itchy.

This tends to start 1 to 2 weeks after treatment begins.

Tell your care team if you notice any soreness or changes to your skin. They may suggest:

  • washing your skin every day with mild, unperfumed soap
  • patting your skin dry instead of rubbing it
  • applying moisturiser to your skin every day
  • not using perfume, perfumed soaps or talcum powder on the area
  • not shaving the area if possible – if you need to shave, use an electric razor instead of wet shaving
  • wearing loose-fitting clothes made of natural fibres, and avoid tight collars, ties or shoulder straps
  • using a high-factor sunscreen (SPF 30 or above) to protect your skin from the sun
  • not swimming in chlorinated water

Skin problems usually settle within 2 to 4 weeks of treatment finishing, but sometimes your skin may stay slightly darker (like it's tanned) than it was before.

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Many people having radiotherapy feel tired (fatigued) a lot of the time or become tired very easily from doing everyday activities.

This usually starts during treatment and can continue for several weeks or months after treatment finishes.

It can help to:

  • get plenty of rest
  • avoid doing tasks or activities that you do not feel up to
  • do light exercise, such as going for short walks, if you're able to – this can boost your energy level, but be careful not to push yourself too hard
  • ask your friends and family for help with everyday tasks

If you're working, you may want to ask your employer for time off or to let you work part-time until your treatment has finished.

Read more tips to help fight tiredness.

Contact your care team if you suddenly feel very tired and out of breath. This can be a sign of a lack of red blood cells (anaemia), which may need to be treated.

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Hair loss is a common side effect of radiotherapy. But unlike hair loss during chemotherapy, it only causes hair loss in the area being treated.

Ask your care team to show you exactly where your hair is likely to fall out.

Your hair will usually start to fall out 2 to 3 weeks after treatment starts.

It should start to grow back a few weeks after treatment finishes, although sometimes it may be a slightly different texture or colour than it was before.

Occasionally, hair loss can be permanent if you have a high dose of radiotherapy. Ask your doctor if this is a risk before starting treatment.

Coping with hair loss

Hair loss can be upsetting. Talk to your care team if you find losing your hair difficult to cope with.

They understand how distressing it can be and can support you and discuss your options with you.

You may decide you want to wear a wig if you lose the hair on your head. Synthetic wigs are available free of charge on the NHS for some people, but you'll usually have to pay for a wig made from real hair.

Other options include headwear such as headscarves.

Read advice about cancer and hair loss.

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Some people feel sick during, or for a short time after, radiotherapy treatment sessions.

This is more likely to happen if the treatment area is near your stomach, or if your brain is being treated.

Tell your care team if you feel sick during or after treatment. They can prescribe anti-sickness medicine to help.

You should stop feeling sick soon after your treatment finishes.

Macmillan has more information about managing sickness and vomiting.

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Radiotherapy can sometimes cause:

  • a sore mouth
  • loss of appetite and weight loss
  • discomfort when swallowing

Sore mouth

Radiotherapy to your head or neck can make the lining of your mouth sore and irritated. This is known as mucositis.

Symptoms tend to happen within a couple of weeks of treatment starting and can include:

  • the inside of your mouth feeling sore – as if you have burned it by eating very hot food or drink
  • mouth ulcers, which can become infected
  • discomfort when eating, drinking and/or talking
  • a dry mouth
  • reduced sense of taste
  • bad breath

Tell your care team if you have any of these problems. They may recommend painkillers or a special mouthwash that can help. Avoiding spicy, salty or sharp foods can also help.

Mucositis usually gets better a few weeks after treatment finishes, although sometimes a dry mouth can be a long-term problem.

Loss of appetite

Feeling sick and tired during radiotherapy can make you lose your appetite, which could lead to weight loss.

But it's important to try to eat healthily and maintain your weight during treatment. Tell your care team if you do not feel you're eating enough.

They may give you tips, such as eating frequent small meals instead of 3 large meals, or refer you to a dietitian.

Discomfort when swallowing

Radiotherapy to your chest can irritate your food pipe (oesophagus) which can temporarily make swallowing uncomfortable.

Tell your care team if this affects you, as you may need to make some changes to your diet, such as eating soft or liquid foods.

You may also be prescribed medicine to reduce the discomfort and in a few cases you may need a temporary feeding tube.

Read more about treatments for swallowing problems.

Swallowing problems usually improve after treatment stops.

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Diarrhoea is a common side effect of radiotherapy to the tummy or pelvic area.

It usually starts a few days after treatment begins and may get a bit worse as treatment continues.

Tell your care team if you get diarrhoea. Medicine is available to help relieve it.

Diarrhoea should disappear within a few weeks of treatment finishing. Tell your doctor if your symptoms have not improved after a few weeks, or if you notice blood in your poo.

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Radiotherapy can sometimes make your joints and muscles in the area being treated feel stiff, swollen and uncomfortable.

Exercising and stretching regularly can help to prevent stiffness.

Tell your care team if joint or muscle stiffness a problem. They may refer you to a physiotherapist, who can recommend exercises for you to try.

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Radiotherapy can have an effect on your sex life and fertility, especially if your lower tummy, pelvic area or groin is treated.

Ask your care team if there's a chance it could affect you.

Sex and fertility issues for women

In women, there's a risk that radiotherapy could cause:

Cancer Research UK has more information about women's sex life and fertility after radiotherapy.

Sex and fertility issues for men

In men, there's a risk that radiotherapy could cause:

Cancer Research UK has more information about men's sex life and fertility after radiotherapy.

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Having radiotherapy can be a frustrating, stressful and traumatic experience. It's natural to feel anxious and to wonder if your treatment will be successful.

Stress and anxiety can also increase your risk of depression.

Speak to your care team if you're struggling to cope emotionally. They can offer support and discuss possible treatment strategies.

Joining a cancer support group may also help. Talking to other people in a similar situation can often reduce feelings of isolation and stress.

The cancer support charity Macmillan Cancer Support has a directory of support groups. You can also call the free Macmillan support line: 0808 808 00 00 (every day, 8am to 8pm).

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Radiotherapy can damage your body's lymphatic system, which is a network of channels and glands that form part of your immune system (the body's defence against illness).

One of the jobs of the lymphatic system is to stop fluid building up in your body. If it becomes damaged, you may experience pain and swelling. This is known as lymphoedema.

It's most common in the arms or legs, but it can affect other areas, depending on the part of your body that was treated.

It may be possible to reduce your risk of lymphoedema by looking after your skin and doing regular exercises. Ask your care team if you're at risk and what you can do to help avoid it.

If you do get it, treatment for lymphoedema can often help keep the symptoms under control.

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Radiotherapy can slightly increase your risk of developing another type of cancer in the years after treatment.

But the chance of this happening is small, and the benefits of treatment generally outweigh the risk.

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