Possible side effects

Side effects may affect you no matter which area of the body you’re having radiotherapy to. It’s important to remember that most people will have a few side effects and they will often be mild. Most people only experience a few of the following:

  • tiredness
  • feeling sick
  • problems with eating and drinking
  • skin reactions
  • flu-like symptoms
  • hair loss
  • changes in your blood.

There are ways to help you manage side effects so they’re easier to cope with. If you need help and advice about dealing with any, speak to your doctor or radiotherapy staff. Most side effects last for about 10-15 days after treatment finishes.

Some people 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.

Before you have radiotherapy, your clinical oncologist will talk to you about any likely side effects. You can ask the oncologist about any you’re particularly worried about.

Side effects of treatment

Radiotherapy affects people in different ways, so it’s difficult to predict exactly how you’ll react to your treatment. The side effects you have will depend on the type of treatment and the area of body being treated.

Before you consent to the treatment, the hospital staff will explain any side effects you may get. They can also give tips on how to deal with them and how they can be treated.

In this section, we discuss the general side effects of radiotherapy that you may experience, whichever part of the body you’re having radiotherapy to.

You may also find it helpful to read about your type of cancer before you start your treatment. It will include information about the possible side effects of radiotherapy. Being aware of these in advance can help you cope with any side effects that may develop.

External radiotherapy tends to cause more general side effects than internal therapy. It’s important to remember that most people will have only a few of the side effects mentioned here, and for many people, they will be mild. The use of modern treatments means that severe side effects are very rare. Most side effects of radiotherapy will continue for about 10–15 days after treatment has finished and then gradually begin to get better. However, symptoms of tiredness may continue for longer.


Not everyone feels tired during radiotherapy treatment but many people do. For example, some people are able to continue working, but others need to take time off work.

Tiredness (fatigue) can continue for weeks to months after your treatment has finished. It can often be made worse by having to travel to hospital each day, or by other treatments such as surgery or chemotherapy.

Managing tiredness

Get plenty of rest but balance this with some gentle exercise, such as short walks. This will give you more energy and help to keep your muscles working. Save some energy for doing the things you enjoy and ask others for help doing chores if these are tiring you out.

We have more information about coping with fatigue.

Feeling sick

Some people find that their treatment makes them feel sick (nausea), and sometimes they may actually be sick (vomit ). This is more likely to happen if the treatment area is near the stomach.

Your clinical oncologist (or sometimes a nurse or radiographer) can prescribe very effective anti-sickness (anti-emetic) drugs if this happens, and they may prescribe them anyway as a precaution. Tell your clinical oncologist or specialist radiographer if you have any nausea or vomiting, and remember that it usually stops once treatment is over.

Managing sickness

You may find it helpful to let someone else cook or prepare food for you, especially if the smell of cooking makes you feel sick. Sipping a fizzy drink slowly through a straw can help with feelings of sickness. Or try crystalised ginger, ginger tea or ginger biscuits. If you’re given anti-sickness tablets, take them regularly, as this is the best way to keep the sickness controlled. Some anti-sickness medicines work best if you take them before your radiotherapy treatment. Ask your doctor, radiographer or nurse to tell you the best time to take your anti-sickness medicines.

We have more information about coping with nausea and vomiting.

Problems with eating and drinking

During your treatment, it’s important to have a healthy diet and to drink plenty of fluids.

At times, you may not feel like eating or you might find that your eating habits change. These may cause you to lose weight. It’s important to try to maintain your weight throughout treatment, as the radiotherapy will have been planned on your body’s shape. Tell the radiotherapy staff if you’re having any problems with eating, as they can arrange for you to talk to the hospital dietitian.

Some people who have radiotherapy to their head and neck area develop swallowing difficulties. If this happens to you, it can be difficult to eat and drink for a time until your swallowing improves. If your oncologist thinks that you may develop swallowing problems, they may suggest a small operation to put a feeding tube into your stomach.

We have more information about how to manage problems with eating and drinking.

Managing eating and drinking problems

Try having small nutritious snacks throughout the day rather than large meals. If food seems tasteless, use seasoning or strong-flavoured sauces. If your mouth is dry, try sucking an ice cube. If you’re losing weight, add extra energy and protein to your diet with everyday foods or by using food supplements.

We have more information about building up your diet if you are having difficulty eating.

Skin reactions

Some people develop a skin reaction while having external radiotherapy. If this happens, it may begin after about 10 days. How your skin reacts will vary depending on the amount of radiotherapy you have. Some people may find that the skin in the treatment area becomes red and sore or itchy. It may become darker with a blue or black tinge. Sometimes the skin will get very sore and it may break and leak fluid, although this doesn’t happen very often. If your skin gets very sore, your treatment may have to be delayed for a short time to allow the area to recover, although this is rare.

The extent of the reaction depends on the area being treated and your skin type. Some people have no skin problems at all. If you have a skin reaction, it will usually settle down 2–4 weeks after the treatment has finished, but the area may stay slightly darker than the surrounding skin.

Managing skin reactions

During your treatment, you should avoid using any deodorants, soaps, perfumes and lotions on your skin other than those advised by the radiographers. If you develop a skin reaction, such as soreness or a change in skin colour, let the radiotherapy staff know as soon as possible. They will advise you on the best way to manage it.

After treatment you’ll need to protect the skin in the treated area from strong sunshine for at least a year. Once any skin reaction has settled down, you should use a suncream with a high sun protection factor (SPF) of at least 30. You should also wear close-weave clothing and use a wide-brimmed hat if your head and neck area has been treated. It’s important to remember that you can burn through clothing if you’re out in hot sun for a long time. You can usually go swimming once any skin reaction has settled down. This is usually within a month of finishing treatment. Remember to use a waterproof suncream if you’re swimming outdoors.

Clothes can sometimes irritate the skin or cause discomfort in the area being treated. Wearing loose-fitting clothes, preferably made of natural fibres rather than man-made materials, can help. You should also avoid wearing tight collars and ties if you’re having radiotherapy to your neck. Bra and handbag straps can cause irritation if they rub against treated skin. If your chest area is being treated, you may be more comfortable not wearing a bra or wearing a vest instead.

We have more information about coping with skin problems.

Flu-like symptoms

If you have palliative radiotherapy given in one or two treatment sessions, you may experience flu-like symptoms. These include headaches, aching joints or muscles, and lack of energy (lethargy). If you also develop a temperature, it’s important to let your radiotherapy team know.

Flu-like symptoms usually settle quickly. Drinking plenty of fluids and getting some rest can help.

Hair loss

Radiotherapy will only cause hair loss in the treatment area. Hair loss can also happen where the radiation beam leaves the body (for example, on the back of the neck), as well as where it enters the body. Ask your clinical oncologist or radiographer to show you exactly where your hair will fall out.

Hair usually begins to fall out after 2–3 weeks. Hair should grow back after treatment finishes. This may take several months, although it depends on the dose of radiotherapy you have. Occasionally, hair loss is permanent. Your radiographer can tell you if any hair loss is likely to be permanent.

Managing hair loss

If you lose the hair on your head, you may want to wear a wig or cover up in other ways. We have more information about hair loss, which gives helpful tips on what you can do to cover up and how to cope with the emotional effects.

Changes in your blood

Radioisotope therapy (such as strontium or samarium) and sometimes external radiotherapy may temporarily reduce the number of normal red and white blood cells produced by the bone marrow. When the number of white blood cells is low, you’re more prone to infection. If necessary, you’ll be given antibiotics to treat any infection. If the number of red blood cells is low (anaemia), you may get tired easily and may need a blood transfusion.

Your hospital team will arrange for you to have regular blood tests if the treatment you’re having is likely to cause your blood count to fall.

It’s very important to let your doctors know if you feel very unwell, if your temperature goes above 38°C (100.4°F), or if you start feeling cold and shaky.

Effects on sexuality

Some women may also have changes to the vagina and men may have difficulty getting or keeping an erection. You may also experience changes in the physical and emotional feelings associated with sex.

We have more information about the effect of radiotherapy on your fertility (fertility in women and fertility in men) and sex life.

Long-term or late side effects of radiotherapy

All cancer treatments can result in long-term side effects. Modern ways of giving radiotherapy aim to limit the risk of permanent side effects. This has meant that the number of people who develop long-term problems is reducing. However, when radiotherapy is also given with chemotherapy, the long-term effects of radiotherapy may be increased.

Before you consent to the radiotherapy, your clinical oncologist will discuss the likelihood of you developing long-term side effects. It’s important that you have the opportunity to talk these through with your oncologist, even though they might not happen to you.

Not everyone has late effects and you can find more information about the possible long-term effects of treatment for your type of cancer.

Second cancers

Radiotherapy can cause cancer, and a small number of people will develop a second cancer because of the treatment they've had. However, the chance of a second cancer developing is so small that the risks of having radiotherapy are far outweighed by the benefits.

If you’re concerned about your risk of developing a second cancer, talk to your cancer specialist.

Back to Radiotherapy explained

Radiotherapy for CLL

Some people with CLL may have radiotherapy to shrink enlarged lymph nodes or an enlarged spleen.

Who might I meet?

You will meet many different specialists before, during and after radiotherapy treatment.