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Side-effects of radiotherapy (Adults)

You're likely to experience some side-effects when having radiotherapy. Some of these will be temporary and others may be long-term. The benefits of having radiotherapy far outweigh the risks.

What are the typical immediate side-effects of radiotherapy?

Generally, the more immediate side-effects will gradually disappear within around 6-12 weeks after treatment finishes. Common side-effects of radiotherapy include:


You're very likely to feel tired during your treatment and, as the weeks of radiotherapy go on, this tiredness could increase. This may be because your body is using its resources to repair any damage to healthy cells caused by the radiotherapy, or because of all the journeys to and from the hospital.

Unfortunately, the feeling of tiredness doesn't go away immediately once the treatment stops and could continue for a number of weeks. Let yourself rest or nap when you need to and don't feel you must fight the tiredness. Try to plan rest breaks into your days even if you're not feeling tired.

Health teams now encourage all patients to do at least 30 minutes gentle exercise every day to minimise radiotherapy-induced fatigue, such as a short walk.

Hair loss

Unfortunately, you will lose some hair during radiotherapy, and this can be quite distressing.

Generally, your hair will only be lost from the places where the radiotherapy beam enters and leaves your head. If, however, you have whole brain radiotherapy, you're likely to lose hair from your whole head. You can talk to your radiographer about where you're most likely to lose hair.

Knowing that there'll be some hair loss means that you can plan ahead. Take a picture of how you usually wear your hair, so that a hairdresser can shape a wig. You could also keep a lock of your hair to match the colour and texture.

Some people have found gradually cutting their hair shorter, or even shaving it all off, before the start of treatment can help it feel less of a shock.

Hair loss usually starts around three weeks after treatment starts. Most hair loss is temporary, and will begin to grow again two or three months after finishing treatment.

Re-growth is often not as thick as it was before, and your hair may not be the same colour or texture. For example, it may be curly, when it was straight before. For some people, hair loss can be permanent.

There are many styles of wig that you can choose from, including synthetic (monofibre) and human hair wigs. And also lots of places that sell hats, bandanas or wigs and hairpieces as practical suggestions for coping with hair loss.

A list of organisations that sell wigs and other headwear is included in our downloadable information about radiotherapy.

You may be entitled to an NHS free synthetic wig.

Skin sensitivity

During or a few weeks after radiotherapy, some people develop changes to their skin in the area being treated, i.e. on your scalp. These can be like sunburn (red, blotchy and itching) in people with pale skin, and darkening of the skin in those who have darker skin.

As your skin will be more sensitive after radiotherapy, you should take care to protect it from strong winds and the sun. Always wear suntan lotion and a sunhat with neck protection when you're outside.

Usually, the sensitivity will fade in the month or so after treatment, but you should keep using high factor sunscreen long-term on the areas of the skin that have had radiotherapy. This is because radiotherapy can permanently destroy the pigment producing cells in your skin. These cells enable you to tan and protect you from sunlight damage and developing skin cancer.

Your health team will be able to give you further guidance if you develop skin sensitivity.

Sickness and reduced appetite

Feeling sick (nauseous)

If you have radiotherapy to the lower part of your brain, you may feel sick or actually be sick following treatment. This can start from around an hour after treatment and last some weeks. Your doctor can give you anti-sickness tablets to manage this.

Reduced appetite

Feeling sick and tired can make some people temporarily lose their appetite during radiotherapy. This can lead to weight loss. You may find it easier to eat several smaller snacks throughout the day, rather than three 'regular' meals. Or ask your health team if they can refer you to a dietitian.

Myelosuppression (slowing of the production of blood cells by the bone marrow)

Radiotherapy can temporarily slow the production of blood cells by the bone marrow. Low blood cell counts are usually not severe enough to cause major problems.

When there is a break from treatment for a few days, blood cell counts usually recover. However, the low levels can sometimes lead to anaemia, increased risk of infection and/or bleeding, such as bruising or nosebleeds.

If you've had radiotherapy to the brain and spine, or if you're also having chemotherapy, you're more at risk of these effects.

Worsening of symptoms

Radiotherapy to the brain can cause swelling in the treatment area. This swelling increases the pressure in the head, so can sometimes make symptoms worse before they get better.

Your doctor might give you steroids to try to prevent this. Your symptoms usually get better in time.

Long-term side effects of radiotherapy

Radiotherapy is given in a way designed to limit the chance of permanent side-effects as much as possible. Very few people develop long-term difficulties.

Once the whole course of treatment is complete, you'll have regular check-up appointments to monitor the effects of your radiotherapy treatment. Generally, side-effects, apart from hair loss, will gradually disappear within around 6-12 weeks.

Occasionally, some side-effects can be longer-term or develop later in life. Your health team will talk through any side-effects with you before any treatment is given.

Long-term effects of radiotherapy could include impacts on:

​Cognitive skills

Cognitive skills include thinking, memory, learning, concentration, decision-making and planning. They also include processing skills, such as recognising and making sense of information from your senses, particularly sight and hearing. If a large part or the whole of your brain is treated, there is a long-term risk of cognitive impairment. Read more about cognition and brain tumours.


If the radiotherapy is delivered near to your eyes, there's a chance of developing a cataract in the lens of the eye several months or even years later. Cataracts can make your vision cloudy, blurred or dim. However, they can usually be easily treated with a simple, small operation. Read more about sight problems and brain tumours.

Hormonal effects

Radiotherapy treatment that includes the pituitary gland at the base of the brain can affect the production of the various hormones that the pituitary controls.

This can cause a variety of symptoms related to functions such as body temperature, growth, salt and water balance, sleep, weight and appetite.

As part of your follow-up after radiotherapy, you may have blood tests to check your hormone levels, but if you notice any new symptoms, you should discuss them with your doctor.

Second tumour

Radiotherapy can cause changes that, over a long period, can lead to a second tumour developing.

However, the benefits of having radiotherapy far outweigh the risks.

Only a small number of people will develop a second cancer because of the treatment they've had.

If you have further questions, need to clarify any of the information on this page, or want to find out more about research and clinical trials, please contact our team:

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