Generally speaking, radiotherapy causes tiredness. The skin in the treatment area can become red and irritated, this may need topical applications to alleviate symptoms.

Other, more specific side effects depend on the structures/organs included in the treatment area. For example; throat or mouth pain, dry mouth, altered taste, thick mucus secretions, swallowing issues and dental problems.

Side effects may include, but are not limited to:

Early or ‘acute’ side effects (usually occur 1-2 weeks after starting treatment, persisting for a few weeks)

Tiredness is a common side effect of radiotherapy and is more likely to occur in the second half of treatment and is variable between patients. This may persist for a few weeks after treatment and usually settles within 4-6 weeks once radiotherapy is completed.

Redness, irritation and soreness in the mouth/throat causing pain and difficulty in swallowing – pain in the mouth and throat can occur a few weeks into radiation therapy relating to mucosal changes, including ulcer formation. This may have an impact on nutrition due to swallowing difficulty. Referral to specialist dietitian will be important during the treatment course to help monitor this. The treating team can advise on pain killers and oral care including mouth washes that may assist in this area. In some cases, a feeding tube may be recommended. This problem can take 4-6 weeks following treatment to improve.

Dry mouth and/or thick mucus – the glands that produce saliva can be affected by radiation resulting in a dry mouth and thick secretions. A dry mouth can be either temporary or permanent. It will be important to keep the mouth moist by drinking water, salt water mouth washes can also help.

Altered taste and/or loss of appetite– some patients report either loss of taste or altered taste e.g. sweet foods may taste salty or metallic. This can have an affect one’s ability to enjoy food and consequently affect appetite. This is usually a temporary problem but for some may be permanent.

Skin changes – redness, swelling and changes in the texture of the skin can occur. Some patients may notice some itching. This usually settles down within 4-6 weeks after treatment and can be relieved by creams on advice from the treating team. Occasionally, the skin can breakdown requiring specialist treatment.

Hair loss – Hair loss can occur in the area that is being treated and at least some of it will be permanent.

Earache or a blocked sensation of the ear can occur due to swelling of the eustachian tube (a tube that connects the middle ear to the back of the nose).

Hoarseness of voice – change in voice may occur if there is swelling and irritation of the voice box from the treatment.

Breathing Difficulty – the airway can become inflamed and swollen within the neck. In some rare cases, this swelling can be significant resulting in noisy breathing which requires a review by your treating team as soon as possible.

Late or long-term side effects (Side effects well after treatment)

Late side effects may occur a few months or years after treatment though they are much rarer than early side effects. Depending on the problem these may occur once and then go or may be more persistent over the long term or may come and go over time.

Likely side effects

  • Dry mouth – for some patients having a dry mouth may persist. It will be important to keep the mouth moist by drinking water regularly.
  • Underactivity of the thyroid gland – an underactive thyroid gland due to radiotherapy can make patients feel tired and lethargic. This can be determined by a blood test and if confirmed can usually be rectified by having thyroid medication.
  • Neck stiffness – sometimes the soft tissues of the neck can become hard and stiff. This may have some impact on neck range of movement, physiotherapy can help if this is the case.
  • Neck swelling – Some patients notice a swelling in the neck, commonly under the chin due to poor flow of lymph fluid. This is usually worse if lymph glands have been removed at surgery. A physiotherapist or occupational therapist who specialises in lymphoedema management can help to manage this. 
  • Swallowing complications – some patients may develop problems with swallowing after treatment such as difficulty and/or pain due to a combination of radiotherapy, surgery and/or the cancer itself.
  • Hair loss – Permanent hair loss can occur in the area that has been treated.
  • Skin changes – thinning and dryness of skin, visible prominent blood vessels and change in skin pigmentation can occur years after treatment.
  • Teeth and jaw issues – the teeth are more at risk of developing tooth decay. It is important to maintain good oral hygiene and regular dental checks after treatment.
  • Change in voice – Hoarseness of voice usually recovers after treatment but in some cases, it may last for several months. Rarely, there may be permanent change in voice quality, especially when the voice box (larynx) is treated.


  • Soft tissue damage causing chronic non healing ulcers (an open sore)
  • Damage to the jaw bone usually after post treatment dental surgery or other trauma. It occurs due to a limited ability to repair and an increased susceptibility to infections.
  • Breathing difficulty due to airway swelling.

Very rarely

  • Nerve/spinal cord injury – Irritation of the spinal cord causing an electric-like sensation with neck flexion can occur several months after treatment. This usually requires no treatment and resolves by itself.

Information and Guidance

Radiotherapy Treatment Process

Click below for a video that shows the external beam radiotherapy treatment process.