Long-lasting low-grade fevers can occur for many reasons. Things like viral or bacterial infections, stress, medications, health conditions, like thyroid issues or autoimmune diseases, and many other conditions can all cause low grade fever.
A fever is when a person’s body temperature is higher than normal. For most people, normal is roughly 98.6° Fahrenheit (37° Celsius).
“Low grade” means that the temperature is slightly elevated — between 98.7°F and 100.4°F (37.05°C and 38.0°C) — and lasts for more than 24 hours. Persistent (chronic) fevers are typically defined as fevers lasting more than 10 to 14 days.
A fever can mean a lot of different things, but most low-grade and mild fevers are nothing to worry about. For people with immune and autoimmune conditions, low grade fever may be more serious, needing immediate medical attention.
Most often, an increase in body temperature is a typical response to an infection, like a cold or the flu. But there are many other less common causes of a persistent low grade fever that only a doctor can diagnose.
A fever alone may not be a reason to call a doctor. Yet, there are some situations where you should get medical advice, especially if a fever lasts more than a few days. The presence of a fever can mean different things for adults, infants, and children.
Infants
For infants under 3 months old, even a slightly higher than normal temperature can mean a serious infection.
Call your pediatrician for a low grade fever if your baby seems unusually irritable, lethargic, or uncomfortable, or has diarrhea, a cold, or a cough. In the absence of other symptoms, you should also see a doctor if a fever lasts continuously for more than three days.
Children
If your child is still making eye contact with you, drinking fluids, and playing, then a low grade fever isn’t likely a cause for alarm. But you should still visit a doctor if a low grade fever lasts for more than three days.
Also, call your child’s pediatrician if your child:
- is irritable or appears very uncomfortable
- has poor eye contact with you
- vomits repeatedly
- has severe diarrhea
- has a fever after being in a hot car
Adults
For an adult, a fever isn’t usually a cause for concern unless it goes above 103°F (39.4°C). You should see a doctor if you have a fever higher than this.
If your fever is lower than 103°F, but lasts for more than three days, you should also visit a doctor.
You should seek immediate medical attention if any of these signs or symptoms accompany a fever:
- strange rash that rapidly worsens
- confusion
- persistent vomiting
- seizures
- pain when urinating
- stiff neck
- severe headache
- throat swelling
- muscle weakness
- difficulty breathing
- hallucinations
Viral infections, like the common cold, are the most common cause of persistent low grade fever, but there are other less common causes.
Respiratory infections
Your body naturally raises its temperature to help kill the bacteria or virus causing an infection. Viruses cause colds and the flu. Colds, in particular, can cause a low-grade fever that lasts more than a few days.
Other symptoms of a cold include:
- stuffy or runny nose
- sore throat
- sneezing
- cough
- fatigue
- lack of appetite
Viral pneumonia and bronchitis are two other types of respiratory infections that can also cause a low grade fever. Along with a fever, chills, and a sore throat, pneumonia and bronchitis come with a cough that persists for weeks.
It’s common for children to experience repeated viral infections which can make a fever seem to last longer than it actually does.
Treatment for viral infections involves rest and fluids until the body fights off the infection. Acetaminophen can reduce a fever if your symptoms are really bothersome. Fever is important in helping the body fight off certain infections, so sometimes it’s best to wait it out.
If the infection is more serious, your doctor may prescribe antibiotics, antiviral drugs, or other medications to help treat the infection.
Urinary tract infections (UTIs)
Persistent fever can signal a hidden urinary tract infection in both children and adults. A UTI is caused by a bacterial infection. Other symptoms include pain and burning while urinating, frequent urination, and bloody or dark urine.
A doctor can examine a urine sample under a microscope to diagnose a UTI. Treatment involves a course of antibiotics.
Medications
A low grade fever can occur about 7 to 10 days after starting a new medication. This is sometimes called drug fever.
Drugs associated with a low grade fever include:
- beta-lactam antibiotics, such as cephalosporins and penicillins
- quinidine
- procainamide
- methyldopa
- phenytoin
- carbamazepine
If your fever is related to a medication, your doctor may adjust your dosage or recommend a different drug. The fever should disappear once the medication is stopped.
Teething (infants)
Teething usually occurs between 4 and 7 months of age. Teething can occasionally cause mild irritability, crying, and a low grade fever. If the fever is higher than 101°F, it’s not likely caused by teething, and you should bring your infant to see a doctor.
Stress
A persistent fever can be caused by chronic emotional stress. This is called a psychogenic fever. Psychogenic fevers are most common in people with conditions often exacerbated by stress, such as chronic fatigue syndrome and fibromyalgia.
Fever-reducing drugs like acetaminophen don’t actually work against fevers caused by stress. Instead, anti-anxiety drugs are the therapy used to treat a psychogenic fever.
Tuberculosis
Tuberculosis (TB) is a highly infectious disease caused by a bacterium called Mycobacterium tuberculosis. Though TB is more common in developing countries, thousands of cases are reported in the United States each year.
The bacteria can remain inactive in your body for years and cause no symptoms. When your immune system is weakened, however, TB can become active.
Symptoms of active TB include:
- coughing up blood or sputum
- pain with coughing
- unexplained fatigue
- fever
- night sweats
TB can cause a persistent, low grade fever, especially at night, which can result in night sweats.
A doctor can use a test called the purified protein derivative (PPD) skin test to determine if you have the TB bacteria. People diagnosed with active TB disease may need to take several medications for 6 to 9 months to cure it; however, newer treatment options take less time.
Autoimmune diseases
Body temperature has been found to be elevated in some people with chronic autoimmune disease, such as multiple sclerosis (MS) and rheumatoid arthritis.
In one
A low grade fever is also a common symptom of RA. It’s thought to be caused by inflammation of the joints.
Diagnosing RA and MS can take time and may require multiple lab tests and diagnostic tools. If you’ve already been diagnosed with RA or MS, your doctor will want to first rule out another viral or bacterial infection as the potential cause of your fever.
If you have an RA — or MS-related fever, your doctor will likely recommend that you drink plenty of fluids, remove extra layers of clothing, and take nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen until the fever passes.
Thyroid issues
Subacute thyroiditis is an inflammation of the thyroid gland. It can cause a low grade fever in some cases. Thyroiditis may be caused by infection, radiation, trauma, autoimmune conditions, or medications.
Other symptoms include:
- muscle pain
- fatigue
- tenderness near the thyroid gland
- neck pain that often radiates up to the ear
A doctor can diagnose thyroiditis by examining the neck and performing a blood test to measure thyroid hormone levels.
Cancer
Certain cancers — lymphomas and leukemias in particular — can cause a persistent and unexplained low grade fever. Keep in mind that a cancer diagnosis is rare, and a fever is a nonspecific symptom of cancer. Having a persistent fever doesn’t usually mean you have cancer, but it can alert your doctor to run certain tests.
Other common symptoms of leukemia or lymphoma include:
- chronic fatigue
- bone and joint pain
- enlarged lymph nodes
- headaches
- unexplained weight loss
- night sweats
- weakness
- breathlessness
- loss of appetite
Depending on the type and stage of the cancer, a doctor may recommend a combination of chemotherapy, radiation, surgery, or other treatments.
Fevers will usually go away on their own. Over-the-counter (OTC) medications can help to lower a fever, but sometimes it’s better to ride out a low fever with fluids and rest.
If you decide to take an OTC medication, you can choose between acetaminophen and NSAIDs like ibuprofen, aspirin, and naproxen.
For infants younger than 3 months, call your doctor first before giving them any medication.
For children, acetaminophen and ibuprofen are generally safe for reducing fever. Don’t give aspirin to children under 12 years old who are recovering from flu-like or chickenpox symptoms because it can cause a serious disorder called Reye’s syndrome.
If your child is younger than 12 years of age, talk with your doctor before giving them naproxen.
For teenagers and adults, acetaminophen, ibuprofen, naproxen, and aspirin are generally safe to use according to the instructions on the label.
Most low grade and mild fevers are nothing to worry about.
However, you should call your doctor if you’ve had a fever for more than three days straight, or your fever is accompanied by more troublesome symptoms such as:
- vomiting
- chest pain
- rash
- throat swelling
- a stiff neck
It’s hard to know when you should call a doctor for a baby or young child. In general, seek medical care if your baby is less than three months old and has any fever at all. If your baby is older than that, you don’t have to see a doctor unless the fever runs above 102°F (38.9°C) or lasts continuously for more than three days.
Continue to monitor your child’s temperature throughout the day. Rectal temperatures are usually the most accurate. Call your pediatrician’s office if you’re not sure what to do.
Many things can cause a low grade fever. Some are health conditions that need medical care, but many are mild and common situations.
When to seek medical care depends on many factors. For infants, a low grade fever can be an indication of something serious, and you’ll need to seek medical care for them. Children may need care if they have additional symptoms along with a low grade fever, such as vomiting, diarrhea, irritability, and others.
For adults, a low grade fever may be nothing to worry about, to it may be a sign or symptom of something more serious. If you have a fever for more than 3 days or have other symptoms like chest pain, a rash, a stiff or painful neck, or throat swelling, seek medical care.
If you have a low grade fever, your doctor or healthcare professional can help determine the cause and the best treatment for you.