I hear a lot of interesting things when I play the “fly-on-the-wall scientist.” Most statements uttered casually between friends can be tested scientifically; at the very least, research has already been done and one only needs to dig a little to find out whether the statement is true. There are many things in life that can be demonstrated true and false. Grab a bowl; let’s pop a serving of buttery science!
You can tell a baby is teething because they are running a fever; or, conversely, because a baby is running a fever it may imply they are teething.
With two siblings-in-law who have both had two kids each in the past 3 years, I hear this one a lot. I hear it from parents, grandparents, and a variety of great aunts and uncles. But does the cutting of gums by teeth cause a fever? I was really curious, and did some digging around.
First of all, what are the typical things that induce fever? According to the Wikipedia article “Fever”,
Fever (also known as pyrexia or controlled hyperthermia) is a common medical sign characterized by an elevation of temperature above the normal range of 36.5–37.5 °C (98–100 °F) due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.
As a person’s temperature increases, there is, in general, a feeling of cold despite an increasing body temperature. Once the new temperature is reached, there is a feeling of warmth. A fever is one of the body’s immune responses that attempts to neutralize a bacterial or viral infection. A fever can be caused by many different conditions ranging from benign to potentially serious. With the exception of very high temperatures, treatment to reduce fever is often not necessary; however, antipyretic medications can be effective at lowering the temperature, which may improve the affected person’s comfort.
So fever is typically considered to be a medical condition associated with the body’s immune response to a foreign agent in the body. On the surface, it might seem unlikely that teething and fever can be correlated (unless teething leads to an opportunistic infection). The pervasion of this lore in parenting suggests there must be a correlation between fever and teething.
So what does research literature state? A recent study by Australian researchers from the year 2000 published in the journal Pediatrics  reported no discernable correlation between elevated infant body temperature and periods preceding tooth eruption (the first day the tooth penetrates through the gum). The only symptom that was elevated was loose stool, and this was reported by parental monitors but not staff monitors of children at daycare centers.
Another independent study in 1999, published in the same journal but performed by researchers from the Cleveland Clinic, also surveyed the frequency of symptoms in teething children. This study similarly windowed around the date of a tooth eruption and looked at a range of symptoms. Their findings are nicely summarized:
Daily symptom data were available for 19 422 child-days and 475 tooth eruptions. Symptoms were only significantly more frequent in the 4 days before a tooth emergence, the day of the emergence, and 3 days after it, so this 8-day window was defined as the teething period. Increased biting, drooling, gum-rubbing, sucking, irritability, wakefulness, ear-rubbing, facial rash, decreased appetite for solid foods, and mild temperature elevation were all statistically associated with teething. Congestion, sleep disturbance, stool looseness, increased stool number, decreased appetite for liquids, cough, rashes other than facial rashes, fever over 102°F, and vomiting were not significantly associated with tooth emergence. Although many symptoms were associated with teething, no symptom occurred in >35% of teething infants, and no symptom occurred >20% more often in teething than in nonteething infants. No teething child had a fever of 104°F and none had a life-threatening illness.
So while biting, drooling, and other oral symptoms were correlated, those like fever or other immune-response related symptoms were not significantly associated with teething.
So the science seems clear: teething and fever are not correlated. If your child has a fever, it is because their immune system is fighting a virus or bacteria, but not because of teething. So it makes more sense to monitor the fever and consult a physician to make sure it’s not a serious problem.
 “Teething and Tooth Eruption in Infants: A Cohort Study” http://pediatrics.aappublications.org/cgi/content/abstract/106/6/1374
 “Symptoms Associated With Infant Teething: A Prospective Study” http://pediatrics.aappublications.org/cgi/content/abstract/105/4/747