Causes of Fatigue and Low Fever

Fatigue and a low-grade fever commonly occur with a lengthy list of illnesses and conditions. These nonspecific symptoms serve as a general immune system alert, signaling an abnormality somewhere in the body. The underlying causes of fatigue and a low-grade fever range from common viral infections to autoimmune diseases to life-threatening cancers. Persistent fatigue and an unexplained fever warrant medical evaluation to determine the underlying cause and appropriate course of treatment.

Causes of Fatigue and Low Fever (Image: vadimguzhva/iStock/Getty Images)

Common Cold

With roughly 1 billion cases occurring annually, the common cold proves a leading cause of fatigue and low-grade fever among Americans. Fever accompanies a cold more commonly in young children than in adults. Other classic symptoms include sneezing, throat scratchiness and a runny nose, which typically resolve in approximately 7 to 10 days. Symptoms lasting longer might indicate a complication, such as sinusitis.

Infectious Mononucleosis

Profound fatigue and a low-grade fever are classic symptoms of infectious mononucleosis, also known as glandular fever. The Epstein-Barr virus causes the illness, which characteristically leads to widespread lymph gland enlargement and a sore throat. The fever typically peaks in the afternoon in most people. Most cases of infectious mononucleosis resolve in approximately 2 to 3 weeks, with the fever gradually waning as the illness clears. Gradually improving fatigue may persist for several months in some people.

Systemic Lupus Erythematosus

Systemic lupus erythematosus, often referred to as lupus, is an autoimmune disorder in which the immune system mistakenly attacks various body organs and tissues. Lupus can cause a variety of symptoms, depending on the tissues involved in the disorder. Overarching symptoms at the time of diagnosis, however, typically include ongoing fatigue and low-grade fevers. Other common symptoms include headaches, joint and muscle aches, hair loss and skin rashes. Development of a low-grade fever and increasing fatigue in someone with lupus might signal an infection or a disease flareup.

Chronic Fatigue Syndrome

Chronic fatigue syndrome -- also known as CFS or myalgic encephalomyelitis -- is a medical condition characterized by persistent fatigue, poor quality sleep, migrating muscle and joint aches, headaches and a low-grade fever. The syndrome most commonly affects women between the ages of 20 and 40. The cause of chronic fatigue syndrome remains undetermined. Treatment typically includes symptomatic therapy for aches and pains, rest, and a low-intensity exercise program.


Shingles, or herpes zoster, is a viral illness caused by reactivation of the chickenpox virus, usually during late adulthood. In most people, the illness begins with fatigue, a low-grade fever, muscle aches, and skin sensitivity or pain in one area of the body. A painful blistering rash follows in approximately 5 days, erupting in the area exhibiting skin sensitivity. The skin lesions usually heal within approximately 4 weeks.


Unexplained fatigue and fever are common symptoms of cancer. Other symptoms that frequently occur with many different types of cancer include unintentional weight loss and skin changes. Localized symptoms -- meaning those that point toward the organs or tissue affected by the cancer -- and diagnostic tests help pinpoint the site of the underlying cancer.

Other Causes

A July 2014 "American Family Physician" review article noted that there are more than 200 causes of ongoing fever in adults. Some of the more common causes have been noted, but there a many other possibilities. Examples of other causes include: -- infections such as HIV or tuberculosis -- inflammatory diseases like Crohn disease -- autoimmune arthritis -- thyroid gland disease -- medication side effects

Distinguishing among the many possible causes of low fever and fatigue requires a thorough review of other symptoms, the timing of these symptoms, along with a complete physical examination and appropriate testing.

Reviewed by: Tina M. St. John, M.D.

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