Radiotherapy Side Effects: Skin, Heart and What to Expect

What is radiotherapy and why is it given?

Radiotherapy uses carefully targeted high-energy radiation to destroy any cancer cells left behind after surgery. According to Cancer Research UK, it is one of the main treatments for breast cancer and is often given after surgery (such as a lumpectomy or mastectomy) to lower the risk of the cancer coming back in the same area. For most people it is given as a course of short daily sessions over a few weeks, usually from Monday to Friday.

The treatment itself is painless and only takes a few minutes each time. Most side effects build up slowly during the course and for a week or two afterwards, then ease off. The NHS explains that radiotherapy is more precise than it has ever been, which means healthy tissue near the breast, including the heart and lungs, can be protected much better than in the past.

This page is general information, not personal medical advice. Everyone's treatment plan is different. Your radiographers, breast care nurse and oncology team know your situation and can give advice that is right for you, so always check with them about your own care.

Short-term side effects: what to expect

Short-term (or 'acute') side effects are the ones that happen during treatment and in the weeks just after it finishes. They are very common and, for most people, temporary. Cancer Research UK lists the main ones below. They vary a lot from person to person, so you may get some, all or none of them.

• Skin changes in the treated area, such as soreness, redness or darkening, dryness and itching.
• Tiredness (fatigue), which often builds up as the course goes on.
• Swelling or a feeling of heaviness in the breast.
• Aches, twinges or stiffness in the breast, shoulder or arm.
• Hair loss in the treated area only (for example under the arm), not the hair on your head.

The NHS notes that skin reactions such as redness, swelling and itching often start around 1 to 2 weeks after treatment begins. Side effects are usually at their worst in the 1 to 2 weeks after the course ends, and then they gradually settle. Cancer Research UK says the skin usually starts to improve about 3 to 4 weeks after treatment finishes, and by around 3 months most short-term effects have eased or gone.

Skin reactions and how to care for your skin

Your skin is the part of the body that takes the radiation first, so skin changes are one of the most common side effects. The treated area may become red, or darker if you have brown or black skin, and feel sore, dry or itchy. In some people the skin can become moist or blister, often where skin folds, such as under the breast. Your radiotherapy team will check your skin regularly and can give you creams or special dressings to soothe and protect it.

Looking after your skin gently can make a real difference. The advice below is based on guidance from the NHS and Cancer Research UK, but always follow the specific instructions your own radiotherapy team gives you, as they may tailor it to your skin and your treatment.

• Wash the area gently with lukewarm water and a mild, unperfumed soap, then pat (do not rub) the skin dry with a soft towel.
• Use only the creams or moisturisers your team recommends, and ask before using anything else on the area.
• Avoid perfume, deodorant, talcum powder and aftershave on the treated skin unless your team says it is fine.
• Wear loose, soft clothing made from natural fibres like cotton to reduce rubbing; some people find going without a bra, or wearing a soft non-wired one, more comfortable.
• Protect the area from strong sun and avoid very hot or very cold things on the skin, such as hot water bottles or ice packs.
• Do not scratch or rub the area, even if it is itchy, and avoid wet shaving the treated skin.

Tell your team if your skin becomes very sore, broken or moist, as there is a lot they can do to help it heal and to keep you comfortable. Sun protection stays important afterwards too, because treated skin can be more sensitive to the sun for a long time.

Tiredness, breast changes and other effects

Tiredness (fatigue) is very common and is not a sign that anything is wrong. Cancer Research UK explains that it often gets worse as the course goes on and can carry on for some weeks after treatment ends, then gradually improves. Daily travel to and from appointments can add to it. Gentle, regular activity such as short walks, resting when you need to, eating well and asking family or friends for practical help can all make tiredness easier to cope with.

Breast changes are also common. During and soon after treatment the breast may feel swollen, heavier, firmer or tender. Over the longer term, radiotherapy can make the breast tissue feel a little firmer or harder, and the breast may look slightly smaller or change shape. This is caused by a normal healing process in the tissue. Some people also notice aches or twinges in the breast for months or even years; these are usually nothing to worry about, but it is always worth mentioning new symptoms to your team.

If you have treatment to the lymph node area under your arm, there is a risk of lymphoedema, which is swelling in the arm or hand caused by fluid not draining away properly. Your team can explain the signs to look out for and how to lower the risk. Tell them early if you notice any swelling, tightness or heaviness in your arm or hand, as early support helps.

Rare heart and lung effects

Because the breast sits close to the heart and lungs, a small amount of these organs can be in or near the treatment area, especially for treatment to the left breast. The good news is that the risk of long-term harm is now very low. NHS hospital information explains that, in the past, treating the left breast was linked with a small increase in the risk of heart problems, but the risk of a heart problem from radiotherapy is generally estimated to be less than 1 in 100, and modern planning reduces it further.

To protect the heart, many hospitals use a simple breathing technique called deep inspiration breath hold (DIBH) for left-sided treatment. As several NHS trusts explain, you take a deep breath in and hold it for a short time during each treatment. This fills the lungs with air and moves the chest wall away from the heart, so less of the heart is in the path of the radiation. Your radiographers will teach you how to do this if it is part of your plan.

A very small area of lung can sometimes become scarred. Cancer Research UK and the NHS note this is rare and may, occasionally, cause a cough or breathlessness months or a few years later. Long-term effects on the heart, when they happen at all, also tend to appear many years after treatment. For the great majority of people, the benefit of radiotherapy in lowering the risk of the cancer returning clearly outweighs these small risks. If you smoke, your team can support you to stop, which helps protect your heart and lungs.

Long-term and late side effects

Most side effects settle within a few weeks, but a few can last longer or appear later. Cancer Research UK describes the main longer-term effects below. They are generally uncommon, and many can be managed well with the right support.

• Permanent changes to the skin's colour in the treated area, or tiny broken blood vessels that look like fine red spidery marks (telangiectasia).
• The breast feeling firmer, harder or slightly smaller, or changing shape, as the tissue heals.
• Lymphoedema (arm or hand swelling) if the lymph node area was treated.
• Stiffness in the shoulder or arm, which gentle exercises from your team or a physiotherapist can help.
• Rarely, weakening of the ribs in the treated area, or, very rarely, a new cancer caused by the radiation many years later.

It can feel worrying to read a list like this, but it helps to remember that serious late effects are rare, and your team weighs up these small risks carefully before recommending radiotherapy. Gentle arm and shoulder exercises, keeping active, protecting treated skin from the sun and going to your follow-up appointments all help you stay well after treatment.

When to get help and support

Most side effects can be eased, and you do not have to wait until your next appointment to ask for help. The NHS advises contacting your radiotherapy or oncology team if you have new side effects, or if existing ones are getting worse or hard to cope with. Always follow any specific advice your own team gives you about who to contact and when.

• Get advice promptly if the treated skin becomes very sore, blistered, broken or weepy.
• Tell your team about a high temperature, feeling generally unwell, or signs of infection in the treated area.
• Report new breathlessness, a lasting cough or chest pain so it can be checked.
• Mention any swelling, tightness or heaviness in your arm or hand, which could be a sign of lymphoedema.
• Speak to your team about tiredness or low mood that is affecting your daily life; support is available.

Your breast care nurse is a great first point of contact and can connect you with support, including help with the emotional side of treatment. UK charities such as Breast Cancer Now and Macmillan Cancer Support also offer free information and helplines.

Charities like ours work to support early detection and fair access to breast cancer care in underserved communities. Everyone deserves clear information and good support through treatment, whatever their background or wherever they live. If cost, travel or other practical barriers are making your treatment harder, tell your team, as they can often help or point you to support.