A high fever is a one that is higher than the normal range, but what constitutes a high fever varies with individuals, according to Mayo Clinic. Adults should consult a doctor if a fever lasts more than three days and is 103 degrees Fahrenheit or more.
The average temperature is 98.6 degrees Fahrenheit (or 37 degrees Celsius). A high fever in itself is not a sickness but is a sign that someone may be sick, WebMD states. Medical treatment often is not necessary. Mayo Clinic recommends that adults should seek help immediately if the fever comes with intense headaches, throat swelling, rashes or other symptoms.