Ongoing mild fevers can arise from a variety of causes. Viral or bacterial infections, emotional stress, certain medications, thyroid disorders, autoimmune conditions, and numerous other issues can all produce a low-grade fever.
A fever occurs when a person’s body temperature is elevated above the typical range. For most people, normal body temperature is approximately 98.6° Fahrenheit (37° Celsius).
The term “low-grade” denotes a slight rise in temperature — roughly between 98.7°F and 100.4°F (37.05°C and 38.0°C) — that persists for longer than 24 hours. Persistent or chronic fevers are often defined as fevers that continue for more than 10 to 14 days.
A fever can indicate many different things, but most mild, low-grade fevers aren’t dangerous. For individuals with immune system or autoimmune disorders, a low-grade fever may be more concerning and could require prompt medical evaluation.
Typically, an elevated body temperature is the body’s response to an infection, such as a cold or influenza. Still, there are many less common reasons for a lingering low-grade fever that only a clinician can identify.
When should you consult a doctor?
A fever by itself may not always warrant a doctor’s visit. However, there are scenarios where medical advice is advised, particularly if a fever persists for several days. Fever implications differ between adults, infants, and children.
Infants
In infants younger than 3 months, even a slight temperature increase can indicate a significant infection.
Contact your pediatrician about a low-grade fever if your baby is unusually fussy, lethargic, seems uncomfortable, or has diarrhea, congestion, or coughing. If no other symptoms are present, see a doctor if the fever continues without interruption for over three days.
Children
If your child is maintaining eye contact, drinking fluids, and playing, a low-grade fever is less likely to be serious. Still, you should consult a physician if the fever continues beyond three days.
Also call your child’s pediatrician if your child:
- is irritable or seems very distressed
- has poor eye contact with you
- is vomiting repeatedly
- has severe diarrhea
- develops a fever after being left in a hot car
Adults
For most adults, a fever is not usually alarming unless it exceeds 103°F (39.4°C). Seek medical care if your temperature climbs above this level.
If your fever remains below 103°F but endures for more than three days, you should also see a doctor.
Obtain urgent medical help if any of the following occur with a fever:
- a rapidly worsening unusual rash
- confusion
- ongoing vomiting
- seizures
- painful or difficult urination
- neck stiffness
- severe headache
- throat swelling
- muscle weakness
- trouble breathing
- hallucinations
What leads to a persistent low-grade fever?
Viral illnesses, such as the common cold, are the most frequent reason for a lingering low-grade fever, though other, less typical causes exist.
Respiratory infections
Your body deliberately raises its temperature to help eliminate the bacteria or virus responsible for an infection. Viruses cause colds and influenza. Colds, especially, can produce a low-grade fever that persists for several days.
Other cold symptoms can include:
- stuffy or runny nose
- sore throat
- sneezing
- cough
- fatigue
- reduced appetite
Viral pneumonia and bronchitis are other respiratory infections that may result in a low-grade fever. In addition to fever, chills, and sore throat, pneumonia and bronchitis are accompanied by a cough that can last for weeks.
It’s not unusual for children to have repeated viral infections, which can make a fever appear to last longer than it actually does.
Treatment for viral infections typically includes rest and staying hydrated while the body clears the virus. Acetaminophen can help lower a fever if symptoms are particularly uncomfortable. Because fever plays a role in fighting certain infections, sometimes allowing it to run its course is appropriate.
If an infection is more severe, a healthcare provider may prescribe antibiotics, antivirals, or other medications to treat it.
Urinary tract infections (UTIs)
A persistent fever may indicate a concealed urinary tract infection in both kids and adults. UTIs result from bacterial invasion. Other signs include pain or burning with urination, frequent urges to urinate, and blood-tinged or dark urine.
A clinician can evaluate a urine specimen under a microscope to diagnose a UTI. Treatment typically consists of an antibiotic regimen.
Medications
A mild fever can develop about 7 to 10 days after initiating a new medication, sometimes referred to as drug fever.
Drugs linked to low-grade fevers include:
- beta-lactam antibiotics, such as cephalosporins and penicillins
- quinidine
- procainamide
- methyldopa
- phenytoin
- carbamazepine
If a medication is the culprit, your physician may change the dose or suggest an alternative drug. The fever usually resolves after stopping the offending medication.
Teething (infants)
Teething generally occurs between 4 and 7 months of age. Teething can sometimes cause mild fussiness, increased crying, and a slight fever. If an infant’s temperature exceeds 101°F, it is unlikely to be due to teething, and medical evaluation is recommended.
Stress
Chronic emotional stress can lead to a persistent fever, a phenomenon known as a psychogenic fever. These fevers are more frequent in people with conditions worsened by stress, such as chronic fatigue syndrome and fibromyalgia.
Antipyretics like acetaminophen are generally ineffective for stress-related fevers. Instead, anti-anxiety medications and stress-management strategies are used to treat psychogenic fever.
Tuberculosis
Tuberculosis (TB) is a contagious disease caused by the bacterium Mycobacterium tuberculosis. While TB is more prevalent in developing nations, thousands of cases are reported annually in the United States.
The bacterium can remain dormant in the body for years without causing symptoms. When the immune system weakens, TB can reactivate.
Signs of active TB include:
- coughing up blood or mucus
- pain when coughing
- unexplained tiredness
- fever
- night sweats
TB can produce a persistent, low-grade fever—particularly at night—often accompanied by night sweats.
A physician can perform the purified protein derivative (PPD) skin test to detect TB exposure. People with active TB may need several medications for 6 to 9 months to eradicate the infection, though newer regimens can be shorter.
Autoimmune diseases
Some people with chronic autoimmune disorders, like multiple sclerosis (MS) and rheumatoid arthritis (RA), may have mildly elevated body temperatures.
In one study, researchers observed that participants with relapsing MS who reported fatigue also had low-grade fevers.
A low-grade fever is also commonly seen with RA, likely due to joint inflammation.
Diagnosing RA and MS can take time and may require multiple laboratory tests and imaging studies. If you already have RA or MS, your clinician will typically rule out other viral or bacterial infections as the cause of your fever first.
If your fever is related to RA or MS, your doctor will probably advise plenty of fluids, shedding extra layers of clothing, and using NSAIDs or acetaminophen until the fever resolves.
Thyroid problems
Subacute thyroiditis, an inflammation of the thyroid gland, can sometimes cause a low-grade fever. Thyroiditis may result from infection, radiation, trauma, autoimmune disease, or medications.
Other symptoms include:
- muscle aches
- fatigue
- tenderness around the thyroid
- neck pain that may radiate toward the ear
A clinician can diagnose thyroiditis by examining the neck and running blood tests to measure thyroid hormone levels.
Cancer
Some cancers—particularly lymphomas and leukemias—can provoke a persistent, unexplained low-grade fever. Remember that cancer is an uncommon cause, and fever alone is a nonspecific symptom. Having a lingering fever does not usually indicate cancer, but it may prompt your doctor to order further testing.
Other typical symptoms of leukemia or lymphoma include:
- long-lasting fatigue
- bone or joint pain
- swollen lymph nodes
- headaches
- unexplained weight loss
- night sweats
- weakness
- shortness of breath
- loss of appetite
Depending on the cancer type and stage, treatment may include chemotherapy, radiation, surgery, or a combination of therapies.
How is a persistent low-grade fever managed?
Fevers often resolve without treatment. Over-the-counter medications can lower a fever, but sometimes it’s preferable to manage a mild fever with rest and fluids while the body recovers.
If you opt to use OTC drugs, choices include acetaminophen and NSAIDs such as ibuprofen, aspirin, and naproxen.
For infants under 3 months, call your healthcare provider before administering any medication.
For children, acetaminophen and ibuprofen are generally considered safe for reducing fever. Do not give aspirin to children under 12 who are recovering from influenza-like illness or chickenpox, as it can cause Reye’s syndrome.
If your child is under 12, consult your doctor before giving naproxen.
For teenagers and adults, acetaminophen, ibuprofen, naproxen, and aspirin are typically safe when used according to label directions.
Prognosis for people with a persistent low-grade fever
Most mild, low-grade fevers are not cause for alarm.
However, call your doctor if you’ve had a fever for more than three consecutive days, or if your fever is accompanied by more concerning symptoms such as:
- vomiting
- chest pain
- a rash
- throat swelling
- a stiff neck
It can be difficult to know when to consult a physician for a baby or young child. Generally, seek medical care if your infant is younger than three months and has any fever. For older infants, you may not need a doctor unless the fever exceeds 102°F (38.9°C) or persists continuously for more than three days.
Keep monitoring your child’s temperature through the day. Rectal measurements are often the most accurate. Contact your pediatrician’s office if you’re uncertain about what to do.
Takeaway
A wide range of issues can cause a low-grade fever. Some are medical conditions that need treatment, while many are mild and common.
When to seek care depends on several factors. In infants, even a small fever can signal something serious and warrants medical evaluation. Children may need medical attention if additional symptoms accompany a low-grade fever, like vomiting, diarrhea, or marked irritability.
For adults, a low-grade fever may be benign or may point to a more significant problem. If you have a fever lasting more than three days or experience other symptoms such as chest pain, a rash, a stiff or painful neck, or throat swelling, seek medical care.
If you have a persistent low-grade fever, your healthcare provider can help identify the cause and recommend the most appropriate treatment.
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