In infants under 3 months, a rectal temperature over 100.4 degrees Fahrenheit means it's time to seek medical attention as soon as possible, but between 3 months and 3 years, that number climbs to 102.2, notes About.com. In older children and adults, the number is 107.6 without any other symptoms.
In most cases, fevers by themselves do not cause harm, and emergency rooms have almost no additional remedies beyond what people have at home, explains About.com. Fever is the body's way to fight infection. When people have fever but still have energy, other than medication for comfort, no treatment is necessary. When other symptoms occur such as aching, medication is necessary.
For younger children, fever is a possible sign of serious illness, and they are too young to indicate other symptoms reliably. With older children and adults, if other symptoms present that cause concern, then medical attention is necessary. If not, maintaining fluids is the best course, reports About.com.