What temp is considered a fever in an adult. and how dangerous is it to have one for several days?

98.6, but...: Normal oral temperature for and adult/child is 98.6 f. 36.8 c. It depends where you take the reading: oral is usually one degree f lower than vaginal or anal readings. You are considered to have a fever if above 100f, but i think if you have a fever close to 102-3 for 2 days or more, it is wise to see a physician. If a child has 101 f for a couple of days, keep hydrated (as with adults) & call md.