Severe fever in adults and severe fever in children vary in their effect on the body. In children, a fever of more than 104°F can have negative effects on the brain and can lead to seizures (called febrile seizures). Thus, a high fever requires prompt medical attention for children less than 36 months. In the case of adults, the need for medical attention mainly depends on what’s causing the fever, but it’s always better to consult your doctor if you run a high temperature for 2–3 days straight with no improvement, regardless of other symptoms.