Breast Cancer Treatment Side Effects

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Side effects of breast cancer treatment vary by the type of treatment, which may include surgery, radiation therapy, chemotherapy or a combination of these.

These side effects occur because cancer treatments not only remove or destroy cancer cells, but also affect normal cells, as listed below.

Surgery: Surgical procedures for breast cancer remove a tumor, but also come with risks, like infections or blood clots.

Chemotherapy: In targeting fast-growing cells like cancer throughout the body, chemotherapy may affect normal cells, too, like hair follicles and the cells inside the mouth.

Radiation therapy: This form of treatment destroys cancer cells by breaking apart their DNA, but nearby healthy cells may be affected, too.

In many cases, side effects from breast cancer treatment may be prevented or managed.

This guide will outline the most common side effects associated with breast cancer treatments.

Hair Loss

Hair loss may be a side effect of certain types of chemotherapy and radiation therapy. It often starts one to three weeks after treatment begins. While hair may start to grow back before treatment ends, it often takes several months.

Chemotherapy medications damage hair follicles, which may cause hair on the head and other areas of the body to fall out. This includes eyebrows and lashes and even pubic hair. Wearing a cooling cap before, during and after chemotherapy treatments for breast cancer may help prevent some hair loss. Once treatment ends, hair typically starts growing back within two or three months. Patients are sometimes surprised by their new hair. It may have a different texture — like curly, wavy or straight — and may be very fine at first. Over time, hair is likely to return to the way it was before treatment.

Radiation therapy may cause hair loss on the part of the body being treated. Hair typically starts growing back three to six months after treatment ends. If doses of radiation are very high, however, hair may be thinner than before. In some cases, it may not grow back at all.

During treatment, it is important to treat hair gently and wash it less often. Patients should use a mild shampoo and avoid styling equipment like blow dryers and curlers. They should do the same when hair begins to grow back.

When they start to lose their hair, many people feel embarrassed, angry or depressed. Talking to friends or family, or finding a support group with people going through a similar experience, may help. Some people wear head scarves or wigs when their hair begins to fall out. Others cut their hair short or shave their heads. It is essential to use sunscreen to protect the head and scalp after hair loss and while it is growing back.

“Chemo Brain”

Cancer-related cognitive impairment, better known as “chemo brain,” refers to treatment-related memory problems, confusion, trouble with concentration, and difficulty thinking and focusing. These side effects may accompany some types of chemotherapy, radiation therapy and immunotherapy for breast cancer. They may start during treatment or after it is complete, and they may begin suddenly or come on more slowly. In some cases, they may last for years after treatment.

The symptoms of chemo brain may be eased by using coping and organization strategies recommended by the care team or specific therapy to improve memory, focus and thinking skills. Stress relief practices like yoga or meditation may also help manage chemo brain. Sometimes, the drug Ritalin^® (methylphenidate), a stimulant, may be prescribed to lessen symptoms. Research shows that getting regular physical activity — at least 150 minutes each week — during and after treatment may help manage symptoms.

Fatigue

Feeling fatigued — that is, tired, exhausted and run down — is one of the most common cancer side effects. Fatigue may have many causes. It may owe to the cancer’s direct effect on the body or to the demands of coordinating appointments and treatment. For most people, fatigue likely stems from several factors at the same time.

Fatigue may also be caused by many types of cancer treatments, as detailed below.

Surgery: This may result in fatigue as the body heals or due to side effects of pain medication. Postsurgical fatigue tends to improve as recovery continues, but it might last longer if other types of treatment are part of a patient’s care plan.

Chemotherapy: Cancer medication may cause fatigue as it destroys healthy cells as well as cancerous ones. This eases after treatment ends, but it may take a month or more for energy levels to return to what they were before.

Radiation therapy: This may cause fatigue that worsens as treatment progresses. Once radiation therapy ends, fatigue tends to ease within a few months.

Immunotherapy, targeted therapy and hormone therapy: These forms of breast cancer treatment may all cause fatigue during treatment, but when it is likely to start and resolve is not as predictable as for other types of treatment.

The care team may be able to offer options for managing fatigue, including medications or supplements that have been shown to improve energy levels. Nutrition and sleep play a big role in fighting fatigue, too, as does physical activity. Counseling or a support group may help patients manage emotions and stress caused by a cancer diagnosis, as well as frustrations owing to side effects like fatigue.

Mouth Sores

Mouth sores are a possible side effect of chemotherapy and radiation therapy, especially those focused on the head and neck. Chemotherapy works by destroying fast-growing cancer cells, but it also may damage normal cells that grow rapidly, like those in the mouth. This leads to an imbalance in bacteria, which sometimes causes mouth sores and oral infections.

At least a month before chemotherapy begins, a dentist with experience caring for people with cancer should provide a preventive oral exam and treat any issues they find. Once chemotherapy begins, good everyday oral care is essential to prevent oral issues like mouth sores. It is important to:

• Brush teeth with a soft brush two to three times a day
• Use a toothpaste with fluoride and a mild flavor to prevent irritation
• Use an alternative if toothpaste is irritating. Mix 1/4 teaspoon of salt with 1 cup of water and use that to brush
• Reduce soreness by rinsing every two hours with a solution of 1/4 teaspoon salt, 1/4 teaspoon baking soda and 1 quart of water
• Floss gently once a day
• Take good care of dentures and other oral appliances by brushing and rinsing them daily, and soaking them in water or a solution made specifically for denture care

Eating healthy foods may help prevent mouth sores as well. The body needs essential nutrients, vitamins and minerals for normal cells to heal from damage caused by chemotherapy and to prevent or fight infection.

Oral side effects like mouth sores from chemotherapy often heal after chemotherapy treatment ends.

Lymphedema

Lymphedema is swelling caused by a buildup of lymph fluid, which mainly flows in tubes just under the skin. Lymph carries excess fluid from cells and tissues into the bloodstream. If the flow of this fluid is blocked, it may cause lymphedema.

It may happen in any part of the body, but it most often occurs in the chest, arm or hand after breast cancer treatment. It may follow surgery to remove one or more lymph nodes, or radiation therapy, which may damage lymph nodes and create scar tissue that blocks lymph fluid flow. Lymphedema affects the side of the body treated.

Lymphedema has its own staging system, much like different types of cancers. The care team may use these stages to describe how severe lymphedema is.

Stage 0: Patient may have no symptoms, but lymph fluid does not move through the body normally.

Stage 1: Area feels swollen, and pressing on it creates a dent in the skin.

Stage 2: Affected area is more swollen and may feel firm to the touch. No dent is left when skin is pressed.

Stage 3: The area is hard, very swollen and movement may be limited. The skin may be blistered and dry.

A nurse, physical therapist, occupational therapist or a certified lymphedema therapist (CLT) may help create a treatment plan for lymphedema, including:

• Compression garments like bandages, wraps, stockings or leggings that prevent lymph fluid from building up
• Lymphatic drainage massage, or manual lymphatic drainage, to help lymph fluid keep moving through the body through gentle massage
• Compression pumps, which are devices that provide gentle squeezes on and off to keep fluid moving
• Surgery for severe lymphedema, including procedures to reestablish the flow of lymph fluid through a different vein or to replace a damaged lymph node with a healthy transplant

Patients may take some steps to help prevent lymphedema, including:

• Drinking enough water
• Eating less salt
• Being active
• Protecting skin by using lotion and wearing gloves for activities like cooking or gardening
• Avoiding clothes with tight elastics or anything that could affect the way lymph fluid moves through the body
• Doing gentle self-massage
• Avoiding the heat and sun, which may make lymphedema worse
• Elevating arms or legs with signs of swelling above the heart when lying down

Seroma

The formation of a seroma — a lump caused by fluid buildup in an organ, tissue or body cavity — is a common side effect of breast cancer surgery. It may occur seven to 10 days after the wound is closed or the wound drain has been removed. It may or may not be painful, limit movement or cause the wound to open again. Most of the time, it goes away on its own and is reabsorbed by the body, though the care team will keep a careful eye on it and watch for any issues, like tissue damage around the wound, infection or severe pain. It is important to follow the care team’s instructions for wound care after surgery.

For a seroma that does not go away on its own, or one that causes pain, limits movement or shows signs of an infection, the care team may drain the fluid using a thin needle, a procedure called a fine-needle aspiration. If the care team thinks there may be an infection, a small amount of the fluid removed will be examined in order to confirm an infection and inform a plan for treatment. Surgery that reopens the wound to drain a seroma is needed only in extreme cases.

Learn more about seroma as a side effect of cancer treatment.

Osteoporosis and Bone Health Problems

Some breast cancer treatments may cause bone health issues like mild bone loss (osteopenia) and severe bone loss (osteoporosis). Loss of bone mass may increase a patient’s risk for fractures. Chemotherapy, radiation therapy, hormone therapy and tyrosine inhibitors — a type of targeted therapy drug — may all affect bone health.

Before treatment, the care team may check bone density with a special X-ray called a DEXA scan in order to gauge the potential impact of cancer treatment. Finding out about potential bone issues early on is key to preventing or managing them once treatment starts. The care team may be able to prescribe medications to help maintain bone density or to slow bone loss during treatment.

Patients in cancer treatment may take several steps to keep their bones as healthy as possible, including:

• Eating for bone health by getting enough protein, vitamin D and calcium
• Walking, dancing and being active on their feet
• Exercising with a resistance band or weights to strengthen muscles and bones
• Stopping all tobacco use
• Avoiding excess alcohol and caffeine
• Following recommendations for bone density testing

Menopausal Symptoms

Some chemotherapy and hormone therapy drugs such as tamoxifen may cause menopausal symptoms such as hot flashes or vaginal dryness in women who have not yet entered menopause. Aromatase inhibitors may cause similar symptoms for women who are already in menopause.

Postmenopausal women might experience a return of hot flashes and other symptoms if they have to stop taking hormone therapy drugs during cancer treatment. These therapies, which are typically used to treat menopausal symptoms in people without cancer, may make breast cancer grow or disrupt cancer treatment.

Adjuvant endocrine therapy, which is typically taken for five to 10 years after cancer treatment, may also cause menopausal symptoms.

Some lifestyle changes may help to relieve hot flashes. It may help to avoid:

• Stress
• Alcohol
• Caffeine
• Diet pills
• Spicy food
• Hot showers
• Hot weather
• Smoking
• Overheated bedrooms

Hot flashes may be treated with non-hormonal medications typically used for other conditions, such as antidepressants, blood pressure medications or seizure medications. Yoga, meditation and acupuncture may also be helpful. And, according to a 2021 review in Supportive Care in Cancer, some women found relief from hot flashes with cognitive behavioral therapy and hypnosis.

Treatment options for vaginal dryness include moisturizers, lubricants and gels made for use in the vaginal area.

The care team works with each patient to help women feel better during their cancer treatment. Patients should feel free to ask questions about menopause or related symptoms and seek care for any side effects that affect their quality of life.

Managing Side Effects at City of Hope

People undergoing breast cancer treatment often face side effects — and they may be different for each patient. To help manage these side effects, City of Hope provides a personal and supportive care team dedicated to helping patients navigate their care. By addressing both physical and psychological needs, City of Hope ensures patients receive holistic care. This helps patients navigate the challenges of treatment side effects and maintain their quality of life through treatment.

Learn more about general physical changes after cancer treatment.