An oral temperature above 98.6 degrees Fahrenheit but below 100.4 degrees Fahrenheit is a low-grade fever. A fever can be symptomatic of many conditions, and the low-grade variety is often not a cause for concern. However, any fever that persists for more than 24 hours warrants a doctor’s visit if the cause is undetermined.
Allergies
Allergies trigger the release of a chemical called histamine, which the body unleashes to attack substances it deems irritating or injurious. Histamine affects the hypothalamus, a region of the brain that is responsible for regulating body temperature, which is why allergies induce a low-grade fever in some people.
Urinary Tract Infections
Cystitis or urinary tract infections (UTIs) can occur when the bladder is inflamed by irritants, such as spermicide or feminine hygiene sprays, or they can result from bacterial infection. Along with myriad symptoms including significant pain and more frequent urination, a person with a UTI may have a low-grade fever as the body combats bacterial growth by triggering an immune response that causes a low-grade fever.
Teething
Teething babies have a range of symptoms, including low-grade fever, that is often mistaken for a cold or similar infection. The process of teeth emerging through gums triggers an inflammatory response, but doctors also believe that babies are prone to low-grade fevers during this time because they are losing the immunity they received from their mothers and developing their own.
Psychological Stress
Though controversial, some evidence suggests that psychological stress affects body temperature. Research indicates that acute stress exposure activates the hypothalamic-medullary-sympathetic or HMS axis, which induces hyperthermia, and an increase in body temperature. When it comes to more chronic or repeatedly stressful situations, data shows that people can experience an ongoing low-grade fever for years.
Walking Pneumonia
Walking or atypical pneumonia is a contagious lung infection caused by the Mycoplasma pneumoniae bacteria. Infected people feel fine and can go about their daily lives, experiencing only mild symptoms, including a low-grade fever and persistent dry cough. These symptoms develop when the bacteria attach to the bronchial epithelium cells and inflame the respiratory pathways.
Rheumatoid Arthritis
Rheumatoid arthritis causes immune system proteins to mistake normal tissues for foreign invaders. The attack response by the immune system often results in a low-grade fever. Ironically, the prescribed immunosuppressants can make people with rheumatoid arthritis more vulnerable to infections and associated fevers.
Drug Administration
One rare side effect of antidepressants is a potentially life-threatening condition called serotonin syndrome. It can develop due to an excess of the neurotransmitter in the blood and cause seizures and fever. Some people exhibit persistent low-grade fever even after the psychotropic drug is discontinued. Research indicates that adjusting antidepressant medications can sometimes trigger a slight fever.
Lupus
Between 30 and 90 percent of people with lupus experience a fever. This may be the only symptom at certain stages of the chronic condition, and many factors can cause it. A low white blood cell count and a fever can signify disease activity or a poor response to a specific medication.
Subacute Thyroiditis
An inflamed thyroid can cause subacute thyroiditis. This disease can go undiagnosed because its symptoms are often flu-like. While it is rare, low-grade fevers of unknown origin that don’t accompany more traditional symptoms are, in some cases, the only signs of an endocrine-based illness.
Childhood Leukemia
Certain cancers, specifically those of the blood, bone, and lymphatic system, often cause a low-grade fever. In the case of childhood leukemia, a lack of adequate red blood cells and protective white blood cells creates an environment that increases susceptibility to infection. In some cases, the fever comes from the body’s response to the infection, rather than the infection itself.