1. Skin reactions
2. Swelling of the breast
3. Pain in the breast or chest area
4. Hair loss in the armpit
5. Sore throat 
6. Tiredness and fatigue
7. Lymphoedema
8. Change in breast shape, size and colour
9. Tenderness over the ribs
10. Late side effects 

1. Skin reactions

Radiotherapy can cause skin reactions. 

Most people have some redness around the area being treated. 

The skin may also: 

  • become pinker or darker over time 
  • feel tender, dry, itchy and sore 
  • peel or flake as treatment goes on
  • blister or become moist and weepy

Skin reactions usually begin around 10 to 14 days after starting treatment, but can happen later or after it has finished. 

Your treatment team will monitor any side effects and advise you how to take care of your skin according to the type of reaction you have. 

Let your treatment team know if you develop a skin reaction. Most skin reactions are mild and should heal within three to four weeks of your last treatment, but some may need treating or monitoring more closely. 

Skincare during radiotherapy 

Looking after your skin during treatment will help prevent infection, reduce pain and keep the area being treated comfortable.

Washing the skin

Wash the treated area gently with warm water and pat the skin dry with a soft towel. 

Skincare products

If you want to use anything on the skin in the treatment area, discuss this with your therapeutic radiographer first. 

Sodium lauryl sulphate, which is found in certain creams, can irritate the skin. It’s best to avoid creams and products containing it.

You can usually use soap and deodorant that suits your skin, unless your treatment team has told you not to.   

Heat and cold

Avoid exposing the treated area to extremes of temperature such as hot water bottles, heat pads, saunas or ice packs during treatment. 

Taking care in the sun 

Avoid exposing the treated area to the sun while having radiotherapy and until any skin reaction has settled down. 

The skin in the treated area will remain sensitive to the sun for some time after treatment. Use a sunscreen with a high sun protection factor (SPF). Apply the cream under clothes too as it’s possible to get sunburnt through clothing. 


You may be advised by your treatment team to avoid swimming during and shortly after treatment. This is because skin changes from radiotherapy can be irritated by chlorine or chemicals in the pool. Also swimwear can cause friction at the treatment site. 

Clothing, bras and prostheses

Friction or rubbing from clothing can cause or worsen skin reactions. 

Wearing clothing made from natural fibres, such as a soft cotton bra or vest, may help. Alternatively, you may prefer to go without a bra.

You’ll usually be advised not to wear an underwired bra until your skin heals. 

If you’ve had a mastectomy and wear a silicone prosthesis, you may find it more comfortable to wear the soft, lightweight prosthesis (softie or cumfie) you used straight after surgery.

2. Swelling of the breast 

Your breast or chest area may appear swollen and feel uncomfortable. This usually settles within a few weeks after treatment. 

If it continues after this time, talk to your specialist or breast care nurse as you may need to be seen and assessed by a lymphoedema specialist. 

3. Pain in the breast or chest area 

You may have aches, twinges or sharp pains in the breast or chest area. 

Although these are usually mild, they can continue for months or even years, but they usually become milder and less frequent over time. 

You may also have stiffness and discomfort around the shoulder and breast or chest area during and after treatment. 

Continuing to do arm and shoulder exercises during radiotherapy and for several months afterwards may help minimise or prevent stiffness or discomfort. 

4. Hair loss in the armpit 

Radiotherapy to the armpit will make the underarm hair fall out on that side. 

Men having radiotherapy will lose the hair on the area of the chest that’s being treated. 

Hair usually starts to fall out two to three weeks after treatment has started and it may take several months to grow back. For some people, hair lost from radiotherapy may never grow back.

5. Sore throat 

If you have radiotherapy to the area around your collarbone or near your breastbone, you may develop a sore throat or discomfort when swallowing. 

If this happens, talk to your radiographer, specialist or breast care nurse. 

It may help to take simple pain relief in liquid form, particularly before eating, until the discomfort improves. 

6. Tiredness and fatigue 

You may feel very tired during or after your treatment. 

Travelling to and from hospital can be tiring. However, many people find they can still manage their daily tasks as usual and some continue to work throughout their treatment. 

Fatigue (extreme tiredness) is a very common side effect of cancer treatment. It may start or become worse after radiotherapy has finished. If you have also had chemotherapy, you may already be experiencing fatigue by the time you start radiotherapy.

7. Lymphoedema 

Lymphoedema is swelling of the arm, hand, breast or chest area caused by a build-up of fluid in the surface tissues of the body. It can occur as a result of damage to the lymphatic system, for example because of surgery or radiotherapy to the lymph nodes under the arm and surrounding area.

If the arm, hand, breast or chest area on the side where the radiotherapy or surgery were carried out swells or feels uncomfortable and heavy, contact your breast care nurse or GP. 

8. Change in breast shape, size and colour 

If you’ve had radiotherapy after breast-conserving surgery, the breast tissue on the treated side may feel firmer than before, or the breast may be smaller and look different. 

Although this is normal, you may be concerned about differences in the size of your breasts, or worry that the difference is noticeable when you’re dressed. 

You can discuss this with your breast surgeon to see if anything can be done to make the difference less noticeable. 

9. Tenderness over the ribs

Tenderness can occur over the ribs during treatment. In some people, this discomfort may continue but it usually improves gradually over time.

10. Late side effects

Some side effects can develop months or years after the end of radiotherapy. However, improvements with the equipment and accuracy in marking the exact areas to be treated have made many of these side effects much less common. 

Serious side effects are very rare and experts agree that the benefits of radiotherapy in reducing the chances of breast cancer returning outweigh the risk of possible side effects. 

Hardening of tissue

Radiotherapy to the breast or under the arm can cause hardening of the tissue. This is known as fibrosis. 

If the fibrosis is severe, the breast can become noticeably smaller as well as firmer. This is rare but may happen several months or years after radiotherapy has finished. 

Broken blood vessels 

You may see tiny broken blood vessels under the skin. This is known as telangiectasia. It’s permanent and there’s no treatment for it.

Effects on the lung or heart

Sometimes after treatment to the breast or chest wall area, part of the lung behind the treatment area can become inflamed, causing a dry cough or shortness of breath. This usually heals by itself over time. 

More rarely, fibrosis of the upper lung can occur, causing similar side effects. 

Although particular care is taken to avoid unnecessary radiotherapy to the tissues of the heart, if radiotherapy is given on the left side you may be at risk of heart problems in future. 

Breath hold technique is thought to reduce the risk of any possible damage to the heart and lungs.

Other effects

Other side effects that can occur later include: 

  • weakening of the bones in the treated area, which can lead to rib and collarbone fractures 
  • damage to the nerves in the arm on the treated side, which may cause tingling, numbness, pain, weakness and possibly some loss of movement 
  • developing another type of cancer in the future
Last reviewed: May 2019
Next planned review begins 2021

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