Although teething may cause a slight rise in body temperature, it's probably not the cause if a child's temperature is higher than 100° F (37.8° C).
When Fever Is a Sign of Something Serious
In the past, doctors advised treating a fever on the basis of temperature alone. But now they recommend considering both the temperature and a child's overall condition.
Kids whose temperatures are lower than 102° F (38.9° C) often don't require medication unless they're uncomfortable. There's one important exception to this rule: If you have an infant 3 months or younger with a rectal temperature of 100.4° F (38° C) or higher, call your doctor or go to the emergency department immediately. Even a slight fever can be a sign of a potentially serious infection in very young infants.
If your child is between 3 months and 3 years old and has a fever of 102.2° F (39° C) or higher, call your doctor to see if he or she needs to see your child. For older kids, take behavior and activity level into account. Watching how your child behaves will give you a pretty good idea of whether a minor illness is the cause or if your child should be seen by a doctor.
The illness is probably not serious if your child:
is still interested in playing
is eating and drinking well
is alert and smiling at you
has a normal skin color
looks well when his or her temperature comes down
And don't worry too much about a child with a fever who doesn't want to eat. This is very common with infections that cause fever. For kids who still drink and urinate normally, not eating as much as usual is OK.