Any body temperature above 102.5 degrees Fahrenheit is considered a high fever, says MedicaLook. Fevers that reach 107 F or higher are exceptionally dangerous, because the majority of humans cannot survive such high internal temperatures. The Mayo Clinic advises that adults should seek immediate medical attention for fevers of 103 F or higher.
High fevers between 103 and 106 degrees F can cause serious side effects such as hallucinations, dehydration, confusion and convulsions, says the Mayo Clinic. Children with high fevers may experience seizures, though the Mayo Clinic notes that fever-induced seizures are rare. Milder side effects of fever include sweating, shivering, weakness and muscle aches. Adults should seek immediate medical attention if a fever is accompanied by severe physical side effects such as rashes, vomiting or seizures, or neurological side effects like severe mental confusion and sensory changes.
Infections are a common cause of fevers, and mild fevers usually are not dangerous on their own, explains WebMD. Treatment for fevers primarily involves treating the underlying issue that caused the fever. Over-the-counter acetaminophen, nonsteriodal anti-inflammatory drugs and naproxen also are used to treat fever. Fever becomes more dangerous when it results from hyperthermia or external factors such as heat stroke and medication side effects.