What Are the Side Effects of Radiation Therapy and How to Manage Them

Quick Answer: What Are the Side Effects of Radiation Therapy?

Radiation therapy commonly causes fatigue, skin changes, and hair loss limited to the treated area. Depending on the site treated, it can also cause brain fog, mouth sores, dry mouth, or urinary and bowel changes. Most side effects are temporary and can be managed with medication, diet adjustments, and supportive care from your oncology team.

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Medically reviewed by Dr. Manish Kumar Sharma, Oncologist (Radiation and Medical Oncology), Felix Hospitals, Noida. Last reviewed: July 2026.

What Are the Effects of Radiation on the Human Body?

Radiation therapy works by damaging the DNA inside cancer cells so that they stop growing and eventually die. The difficulty is that the radiation beam cannot always tell a cancer cell apart from a healthy one nearby, so some normal cells in the treatment path get affected too. This radiation effect on human body varies so much from person to person because it depends on the radiation dose, the number of sessions, the exact part of the body being treated, and how healthy the patient is going into treatment.

Doctors classify radiation therapy in two broad ways: external-beam radiation, where a machine directs high-energy beams at the tumour from outside the body over a series of outpatient sessions, and internal radiation (brachytherapy), where a radioactive source is placed inside or very close to the tumour itself, commonly used for prostate and gynaecological cancers. The radiation effect on human body tissue is broadly similar between the two, though brachytherapy side effects tend to be milder since the radiation is more localised and the surrounding healthy tissue receives a lower dose overall.

Most healthy cells that are affected do recover over time, which is why many side effects fade in the weeks or months after treatment ends. Broadly, doctors group radiation after effects into two categories:

• Early (acute) side effects: These begin during treatment or shortly after and usually settle within a few weeks to a couple of months. Fatigue and skin irritation in the treated area are the most common examples.

• Late (long-term) side effects: These can appear months or even years after treatment ends and depend heavily on the radiation dose and the tissue involved.

Because the effects of radiation are so closely tied to the treatment site, it helps to look at the whole-body picture first before going into specific areas such as the brain, the mouth and tongue, or the prostate.

What Are the Side Effects of Radiation on the Brain?

Radiation to the brain is generally used for primary brain tumours or for cancer that has spread to the brain from elsewhere in the body. The side effects of radiation on the brain are different from those seen elsewhere in the body because brain tissue is directly involved in memory, concentration, and day-to-day thinking.

The most talked about long-term concern is cognitive change, commonly described as brain fog. This can include:

• Difficulty with short-term memory and recalling new information

• Slower processing speed or trouble concentrating

• Reduced attention span and difficulty multitasking

• In rare cases, more marked confusion or word-finding difficulty

Cognitive changes after cranial radiation are common, but they are not always permanent. Encouragingly, research presented at major radiation oncology conferences has found that a meaningful proportion of patients who develop cognitive decline after brain radiation regain much of their function within about six months, particularly with modern, more targeted radiation techniques that spare healthy brain tissue as much as possible. Other early effects of brain radiation can include scalp hair loss, mild headache, and temporary swelling that is usually managed with steroid medication during treatment.

What Are the Side Effects of Radiation Therapy for Tongue Cancer?

Radiation therapy for tongue cancer side effects mainly affect the mouth and throat, since the treatment field sits so close to the salivary glands, gums, and the lining of the mouth itself. Radiation therapy for tongue cancer side effects typically include:

• Oral mucositis: painful inflammation and ulcers on the tongue and inside the mouth, usually starting around the second week of treatment

• Dry mouth (xerostomia): caused by reduced saliva production, which can make chewing, swallowing, and speaking harder

• Altered or reduced sense of taste, sometimes described as a metallic taste

• Jaw stiffness, making it harder to open the mouth fully

• Voice changes or hoarseness, and difficulty swallowing

Most of these mouth-related side effects improve gradually over six to eight weeks after treatment ends, though dry mouth and taste changes can take longer to settle and, for some patients, may be permanent. Your oncology team will usually recommend a dental check before starting treatment, since teeth and gums need extra care during and after radiation to the head and neck region.

What Are the Side Effects of a 5-Day Radiation Course?

Many patients are surprised to learn that some cancers, particularly early-stage prostate cancer, can now be treated with a short, highly targeted course delivered over about five sessions instead of the traditional several-week schedule. This approach is known as Stereotactic Body Radiation Therapy (SBRT), and it uses higher, more precise doses per session so the whole course finishes faster.

The side effects of 5 day radiation are generally similar in type to standard radiation therapy, just compressed into a shorter timeline. Commonly reported effects include:

• Mild fatigue, often most noticeable in the days right after finishing treatment

• Localised skin irritation in the treatment area

• Urinary symptoms such as increased frequency or a burning sensation, when the pelvis is treated

• Bowel changes such as looser stools or mild rectal discomfort, when the pelvis is treated

Clinical studies following patients through a five-fraction SBRT course for prostate cancer have generally found that most side effects of 5 day radiation are mild to moderate, with severe reactions being uncommon, and that treatment is completed as planned in the vast majority of cases. Because each session delivers a larger dose, careful planning and image guidance are used to protect nearby healthy tissue such as the bladder and rectum. Patients considering this option often ask whether the side effects of 5 day radiation are worse than a standard multi-week course in practice, the type of side effects is similar, only the timeline is shorter, so symptoms tend to appear and resolve more quickly.

What Are the Side Effects of Radiation Treatment for Prostate Cancer?

Prostate cancer radiation treatment side effects mostly fall into three groups: urinary, bowel, and sexual. Since the prostate sits close to the bladder and rectum, radiation aimed at the prostate can affect these neighbouring structures as well. Radiation therapy for prostate cancer side effects are among the most researched in oncology, since prostate cancer is one of the most common cancers treated with radiation worldwide.

The side effects of radiation treatment for prostate cancer commonly include:

• Urinary symptoms: increased frequency or urgency, a burning sensation while urinating, or in some cases mild incontinence

• Bowel symptoms: diarrhoea, rectal discomfort, urgency, or occasional mild rectal bleeding

• Sexual side effects: erectile dysfunction, which can develop gradually over months as radiation affects the nerves and blood vessels supplying the area, along with reduced libido or changes in ejaculation

• General fatigue during the treatment course

Radiation treatment prostate cancer side effects usually start in the second or third week of a standard multi-week course and improve gradually in the weeks and months after treatment ends, though bowel and sexual side effects can take longer to settle and occasionally persist long-term. A smaller number of men notice radiation treatment prostate cancer side effects appearing only months after finishing treatment, particularly bowel urgency and erectile dysfunction, since these tissues can take longer to show the effects of radiation exposure. Pelvic floor exercises, dietary adjustments, and medications for erectile dysfunction are commonly used to manage these effects, and your urology and oncology teams will usually work together on this.

Whether radiation is delivered through external-beam therapy over several weeks or through a shorter SBRT schedule, the underlying side-effect pattern is similar. What differs is the pace at which symptoms appear and settle, which is why your oncologist will discuss which approach suits your specific cancer stage, general health, and personal preference.

Can Radiation Cause Hair Loss?

Yes, but with an important distinction: radiation therapy causes hair loss only in the specific area that receives the radiation beam, not all over the body. This means hair loss from radiation to the brain typically affects the scalp, while radiation to the chest, abdomen, or pelvis does not usually cause scalp hair loss at all.

So can radiation cause hair loss in the long term? For most patients, hair in the treated area grows back within a few months of finishing treatment, though at very high cumulative doses (as sometimes used for certain brain tumours), regrowth can be thinner or, less commonly, permanent in that specific area. This is different from chemotherapy, which more often causes hair loss across the whole scalp and body because it circulates throughout the bloodstream rather than targeting one area.

How Can You Manage Radiation Therapy Side Effects?

Most radiation after effects can be reduced with simple, consistent daily habits alongside any medication your oncology team prescribes. Here is a quick-reference guide to managing the most common side effects.

Keeping your care team informed is one of the most useful things you can do. Reporting side effects early, rather than waiting for them to worsen, allows your oncologist to adjust supportive medication or, if needed, the treatment schedule itself.

How Can You Cope With Radiation Therapy Beyond the Physical Side Effects?

Radiation therapy is not only a physical experience. Many patients describe feeling anxious before sessions, low in mood during treatment, or simply overwhelmed by the number of appointments and decisions involved. This is a normal response to a demanding treatment schedule, and it is worth addressing alongside the physical side effects rather than after them.

• Talk to your care team about how you are coping, not just about physical symptoms

• Lean on family, friends, or a support group of people going through similar treatment

• Keep a simple daily log of side effects and mood, which also helps your doctor track patterns over time

• Ask your oncology team about counselling or psycho-oncology support if anxiety or low mood is affecting daily life

Practical planning also helps reduce stress. Arranging transport to sessions in advance, keeping a list of questions for your oncologist, and involving a family member in appointments can make the treatment course feel more manageable from start to finish.

When Should You See a Doctor? Warning Signs After Radiation Therapy

Most radiation side effects are manageable at home with your care team's guidance, but some symptoms need prompt medical attention. Contact your oncology team or visit the emergency department if you notice:

• High fever above 38.5°C, especially with chills

• Severe vomiting or diarrhoea that prevents you from keeping fluids down

• Heavy or persistent bleeding from the rectum, urine, or treated area

• Sudden, severe headache, confusion, or seizure after brain radiation

• Difficulty breathing or chest pain

• Signs of infection at the treatment site, such as increasing redness, warmth, or pus

• Inability to urinate or complete blockage of urine flow

Call Felix Hospitals: +91 9667064100, 24x7 Oncology and Cancer Care, if you or a loved one experiences any of these warning signs during or after radiation therapy.

Why Choose Felix Hospitals for Radiation Therapy and Cancer Care in Noida

Managing radiation side effects well starts with a treatment plan built around the individual patient, not a one-size-fits-all protocol. At Felix Hospitals, our oncology team combines dual specialty training in radiation and medical oncology with a molecular tumor board approach, so that treatment planning and side-effect management are considered together from day one.

References

Clinical guidance in this article is consistent with information from the American Cancer Society, the National Cancer Institute (NCI), the American Society for Radiation Oncology (ASTRO), and Cancer Research UK.

About the Reviewer

Dr. Manish Kumar Sharma

Dr. Manish Kumar Sharma is an Oncologist at Felix Hospitals, Noida, with over 9 years of experience in Radiation and Medical Oncology. He holds dual specialty training (DNB Radiation Oncology, DM Medical Oncology), is active in molecular tumor board work for personalised cancer treatment, and has authored multiple research publications. He is a member of several national and international oncology organisations and is the designated reviewer for all cancer and oncology-related content at Felix Hospitals.