A fever indicates an elevated body temperature, often signaling the body is fighting an infection or illness. This natural defense mechanism increases body heat to combat invading germs. While fevers are common and typically resolve without serious complications, extremely high temperatures can be a cause for concern.
Understanding Fever Ranges
Normal human body temperature typically ranges from 97.7°F to 99.5°F (36.5°C to 37.5°C). Most healthcare providers define a fever as an oral temperature of 100.4°F (38°C) or higher.
A low-grade fever generally falls between 99.5°F (37.5°C) and 100.3°F (37.9°C). Moderate-grade fevers are typically in the range of 100.6°F to 102.2°F (38.1°C to 39°C). A high-grade fever is considered a body temperature between 102.4°F (39.1°C) and 105.8°F (41°C).
Critical Fever Temperatures and Associated Risks
Certain fever temperatures are medical emergencies and carry significant risks, varying by age. For infants younger than three months, a rectal temperature of 100.4°F (38°C) or higher warrants immediate medical attention due to the possibility of a serious infection, as their immune systems are not fully developed. In children, a fever reaching 105°F (40.6°C) or higher is a medical emergency. High fevers in young children, often above 102.2°F (39°C), can trigger febrile seizures. While frightening, these seizures are usually brief and do not typically cause long-term harm or indicate epilepsy.
For adults, a fever of 103°F (39.4°C) or higher suggests medical consultation. Fevers above 105.8°F (41°C) can be dangerous, causing organ malfunction and failure. Temperatures exceeding 106.7°F (41.5°C), known as hyperpyrexia, can lead to permanent organ damage and death. Such extreme temperatures can also result in dehydration, increased stress on organs like the heart and lungs, and mental state changes such as delirium.
Recognizing Accompanying Warning Signs
Temperature alone does not always indicate a fever’s severity; other symptoms can signal a serious underlying condition. In adults, severe headaches, stiff neck, unusual sensitivity to light, confusion, or altered speech alongside a fever require prompt medical evaluation. Persistent vomiting or diarrhea, abdominal pain, and skin rashes that appear as purple spots are also concerning signs.
For children, signs such as extreme sluggishness, difficulty waking up, inconsolable crying, or difficulty breathing are serious indicators. A rash, particularly one that does not fade when pressed, can signal a severe illness. A stiff neck, severe headache, or unusual irritability in a child with a fever also warrants immediate medical attention.
When Immediate Medical Attention is Needed
Seeking prompt medical attention is important when a fever is accompanied by worrying symptoms. For older children, a fever persisting for more than three days, or one exceeding 104°F (40°C), warrants medical advice.
Adults should contact a healthcare provider if their temperature reaches 103°F (39.4°C) or higher, particularly if it does not decrease after medication or if they have existing heart or lung conditions. Immediate emergency care is necessary for anyone experiencing a fever along with symptoms like confusion, severe headache, stiff neck, difficulty breathing, or seizures, as these could indicate a serious illness.