What is low-grade fever? A fever is an increase in the body temperature above normal. A low-grade fever is a mild elevation of the temperature above normal. Your temperature measurements fluctuate through the day and vary depending upon the site of measurement. Generally, a child is considered to have a fever if the temperature is at or above 100.4 degrees Fahrenheit rectally, 99.5 degrees Fahrenheit orally, or 99 degrees Fahrenheit in the armpit. In an adult, a fever is generally defined as 100 degrees Fahrenheit (37.8 degrees Celsius) or greater Fevers often accompany infections and are part of your body’s natural defense against them. Body temperature can also be elevated by physical activity and environmental factors, such as wearing heavy clothing or a high ambient temperature. A low-grade fever may also occur following immunizations, during teething, or as a symptom of cancer or inflammatory and autoimmune conditions. It can also occur as a side effect of some medications. Low-grade fevers may not require treatment if other symptoms are absent. Self-care measures, such as rest and drinking fluids, may be enough. Medications, such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), and aspirin, can all lower a fever, although aspirin should not be used for children, and ibuprofen is not recommended for infants under six months of age. Persistent fevers or high fevers may require medical intervention, as may those accompanied by such symptoms as sore throat, earache, cough, or burning with urination. Fevers can be serious in people who have weakened immune systems or who have chronic medical problems. Low-grade fevers can occasionally accompany serious medical conditions. Seek immediate medical care (call 911) for serious symptoms, such as irritability or inconsolability in children, confusion, decreased levels of consciousness, difficulty breathing, difficulty walking, severe pain, neck rigidity, seizure, blue coloration of the lips or nails, or rapid heart rate. If your low-grade fever is persistent or causes you concern, if you have other symptoms of infection, a weakened immune system, or have chronic medical problems, seek prompt medical care.