Fatigue is a feeling of physical or mental exhaustion, or lack of energy. Causes of fatigue include illness, lack of exercise, or too much exercise, stress, and depression.


Fatigue is a condition characterized by extreme tiredness and a lack of energy. Unlike general tiredness, the fatigued person usually does not feel better after a full night of sleep. Fatigue can be a symptom of chronic dehydration, a poor diet, and conditions such as the flu, cancer, and depression. Types of fatigue range from acute fatigue that comes on suddenly and is a symptom of the flu, to a more severe fatigue caused by an ongoing stressful situation. In both instances, people might feel exhausted and have difficulty concentrating. They could feel like sleeping most of the day, their muscles might ache, and they might feel weak.

Some types of fatigue can be treated at home; others require medical treatment. For example, after a person recovers from the flu, fatigue is replaced by a feeling of well-being and more energy. Individuals in stressful situations need to resolve issues causing the stress or find healthy ways to cope with stress. For some fatigued people, that stress could be caused by work or a family matter; for others the stress and fatigue could be related to a condition such as pregnancy, cancer, AIDS (acquired immune deficiency syndrome), or multiple sclerosis. Those physical and mental health conditions are treated medically.

Another form of fatigue is chronic fatigue syndrome, a condition in which an individual experiences severe and persistent fatigue that lasts more than six months, a condition that requires medical treatment.

Although the range of fatigue varies in severity, exercise and a nutritious diet are among the ways to reduce fatigue in people with acute fatigue and in those who have more severe fatigue or chronic fatigue syndrome.


Fatigue is a symptom of numerous conditions, so it is likely that people of all ages will experience some form of fatigue during their lives. It can be caused by an illness, such as the flu, that affects all age groups. Children and adults might feel exhausted by schoolwork or job duties; they might also feel bored because of an ongoing lack of mental stimulation. In addition, chronic conditions, such as cancer, affect children and adults. Estimates of chronic fatigue among adults range from 10% to 40% and likely average about 20% of American adults. Fatigue is the cause of up to 20% of fatal vehicle accidents. The people most likely to have fatigue-related driving accidents are young people, shift workers, and those who have sleep disorders.

Causes and symptoms

Mental and physical fatigue are usually symptoms of another condition such as an illness, mental health condition, or stress brought on by factors, such as school or work pressures. Head injuries also can cause fatigue. Lifestyle could produce fatigue, if a person is inactive and does not follow a healthy diet. Furthermore, some medications can produce fatigue.

Symptoms of fatigue can include lack of energy, weakness, a feeling of constant exhaustion, and difficulty concentrating. The fatigued person might lack motivation and have difficulty beginning or finishing a task. An individual can experience some or all of these symptoms.

Mental health

The mental health conditions that cause fatigue include anxiety, depression, grief, and stress.

For a person diagnosed with a generalized anxiety disorder, the long-term condition involves constant worry about small and major issues. Other anxiety disorders include obsessive-compulsive disorder and post-traumatic stress disorder.

DEPRESSION. Depression is a chronic illness like diabetes rather than a temporary sense of extreme sadness or disappointment. It affects the mind and body, and generally requires long-term treatment. The person diagnosed with this condition may have trouble accomplishing routine tasks and could feel hopeless about life.

GRIEF. The death of a loved one causes grief. This natural process allows a person to heal after the shock of the loss and the realization that the deceased is no longer part of one's life. The grieving person experiences symptoms similar to those associated with depression.

STRESS. Stress is the way a person reacts mentally, physically, and emotionally to change and unexpected situations in life. The situation can be a happy event, such as an upcoming marriage, which causes positive stress, or an event that seems overwhelming, such as the diagnosis of cancer. This causes distress, or negative stress.

Stress is a chemical reaction that warns the body of the need to take action. The person becomes tense, preparing to either deal with a situation or avoid it. That reaction has been with humanity since primitive times, when the warning to fight or flee was crucial to survival. Then and now, the body stops sending the warning when it senses the person is out of danger.

The stress process creates tension, and the person who does not find a way to release that tension could experience symptoms that include fatigue.

SCHOOL AND WORKPLACE FATIGUE. Fatigue for students and workers could be caused by boredom or overwork. For some students, fatigue might result from an ongoing lack of being challenged. At the opposite end of the spectrum is a heavy study load.

Adults who do repetitive work, such as assembling parts, might experience mental and physical fatigue caused by the boredom of doing the same task repeatedly, and this could place the worker at risk for injuries. In addition, the individual might make mistakes or become less productive.

Workplace fatigue could also be caused by an extended-hour schedule that requires people to work more hours on some days. They might work 10 hours on Monday through Thursday, and then have a day off on Friday. The work week is shorter, but employees have less free time after the workday ends. They might feel they only have time to “do their job, eat, and sleep,” according to a document from the Canadian Centre for Occupational Health & Safety.

Chronic conditions and fatigue

Fatigue is associated with health conditions, including cancer, AIDS, and muscular dystrophy. For example, fatigue could be a symptom of cancer. In addition, treatment, such as radiation therapy, for people diagnosed with cancer also causes fatigue. This is a normal reaction, according to the National Cancer Institute.


Fatigue could result from medications that cause drowsiness. These medications include antihistamines used to treat allergies, medicines to regulate blood pressure (e.g., diuretics), sleeping pills, and steroids.

Chronic fatigue syndrome

In 2015, the Institute of Medicine recommended changing the name of chronic fatigue syndrome to systemic exertion intolerance disease (SEID) The cause of SEID is not entirely clear as of 2017. Most likely, the disease is related to possible infections and immune system problems. Symptoms generally develop rapidly in someone who previously had been healthy. SEID is characterized by flu-like symptoms that last more than six months. These symptoms include fatigue, a mild fever, sore throat, swollen lymph glands, unrefreshing sleep, a low-grade fever, joint pain, muscle pain or weakness, and headaches. A hallmark symptom is extreme fatigue following exercise or other exertions. There is no treatment or cure, but doctors can help people manage their symptoms.

Diet and exercise

Just as a car requires regular maintenance to run smoothly, the body needs a nutritious diet and regular exercise to remain healthy.

DIET. A poor diet will cause fatigue because the body does not receive the essential nutrients that are needed to provide energy and ongoing body maintenance, such as tissue replacement. Food should be the source of the six essential nutrients: protein, carbohydrates, fats, vitamins, minerals, and water.

Acquired immune deficiency syndrome, caused by infection with the human immune deficiency virus (HIV). The disease causes problems with the function of the body's immune system.
A condition caused by lack of healthy red blood cells (hemoglobin). Anemia leads to chronic fatigue.
Ongoing or long-lasting. A chronic illness or condition can last several months or a lifetime.
Chronic fatigue syndrome—
A complex disorder with unknown cause that leads to extreme fatigue that can get worse when a person is physically or mentally active.
Multiple sclerosis—
A chronic disease of the central nervous system that can cause disability when information between the brain and the body is disrupted.
A laboratory test of a urine sample usually to screen for or detect a disease.

In addition, blood volume is reduced when people fail to drink enough water each day. This causes dehydration, which can produce fatigue.

EXERCISE. Regular exercise also helps to maintain health. The person who is inactive neglects activities that build and maintain bones, muscles, and joints. This also increases the risk of fatigue-producing conditions such as stress, diabetes, and high blood pressure.


Mild forms of fatigue known as acute fatigue usually do not need a medical diagnosis because the person is aware of the cause and knows how to resolve the issue. The individual with the flu or cold knows that the condition will improve. Individuals experiencing stress might be aware of methods to relieve tension and the related fatigue. If not, they should seek medical attention. Furthermore, medical treatment for those diagnosed with a chronic condition such as cancer should include information about how to reduce or eliminate fatigue. For the person unsure about the cause of the fatigue, medical attention is required.

Medical diagnosis

Fatigue is related to numerous conditions, so a doctor will usually perform a complete examination. The exam will focus on the heart, lymph nodes, thyroid, and nervous system. The doctor will also discuss the patient's symptoms and medical history. Questions about symptoms include whether the person has experienced fatigue in the past. Questions about the current situation include how long the person has felt fatigued and if the person has trouble falling asleep or difficulty staying asleep.

The doctor will ask about the patient's life, because the fatigue may be related to a death in the family or an extended workday schedule. The doctor will also ask questions about the patient's feelings, diet, frequency and type of exercise, and habits such as smoking or drinking alcohol and caffeinated beverages.

Then, the doctor may prescribe treatment or order tests—a blood test to check for an infection or conditions such as anemia or diabetes; a urinalysis; and/or tests of thyroid, kidney, and liver function—to determine the disease or condition causing the fatigue. If needed, the physician may refer the patient to a mental health professional for counseling.

Because the cause of SEID (chronic fatigue syndrome) is not known, it is diagnosed by eliminating other conditions that could cause similar symptoms. Doctors in the 2000s began developing criteria to help with diagnosis of chronic fatigue, including whether the patient has malaise following exertion. For example, it is more difficult to perform the same exercise on the second day than it was the day before.


Home treatment should help with some causes of fatigue. This starts with regularly exercising, eating a healthy diet, and getting enough sleep. People might need to make changes to their lives, such as reducing the amount of caffeine consumed, eliminating a medication that produces fatigue, trying to adjust a work schedule, or finding other employment.


A person may need to seek counseling to work through issues such as depression or stress related to a family matter. Medication might be prescribed to manage depression or other conditions.


Treatment helps end fatigue for some people, but those diagnosed with a chronic condition could face long-term fatigue. Treatment measures, including regular exercise, rest, and a healthy diet, should lessen the severity of the fatigue and allow the individual to function.


Exercising regularly will help to prevent mild fatigue and relieve stress. A healthy diet is also beneficial, as is getting enough sleep. In addition, individuals need to deal with the underlying causes of fatigue. In some cases, this involves working to resolve issues that cause stress, such as a heavy workload. If unable to resolve the issue, an individual should concentrate on releasing the tension through relaxation techniques, such as deep-breathing exercises. These are helpful for both emotional stresses, such as work overload, and for health issues, such as SEID (chronic fatigue syndrome), or chronic medical conditions like cancer.



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Centers For Disease Control and Prevention. “Chronic Fatigue Syndrome.” US http://www.cdc.gov/cfs (accessed March 2, 2017).

Crawford, Chris.“Chronic Fatigue Syndrome: Renamed and Redefined.” AAFP.org . http://www.aafp.org/news/health-of-the-public/20150302newchronicfatigue.html (accessed March 2, 2017).

Cunha, Burke A. “Chronic Fatigue Syndrome Treatment.” Medscape. http://emedicine.medscape.com/article/235980-treatment (accessed March 2, 2017).

Mayo Clinic Staff. “Fatigue.” Mayo Foundation for Medical Education and Research. http://www.mayoclinic.com/health/fatigue/MY00120 (accessed March 2, 2017).

National Cancer Institute. “Managing Radiation Therapy Side Effects.” US Department of Health & Human Services. http://www.cancer.gov/cancertopics/coping/radiation-side-effects/fatigue.pdf (accessed March 2, 2017).


American College of Sports Medicine (ACSM), 401 W. Michigan St., Indianapolis, IN, 46202-3233, (317) 6379200, Fax: (317) 634-7817, http://www.acsm.org .

Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA, 30333, (800) 232-4636, cdcinfo @cdc.gov, http://www.cdc.gov/

Liz Swain
Revised by Teresa G. Odle, BA, ELS

  This information is not a tool for self-diagnosis or a substitute for professional care.