Teething itself doesn’t make babies sick. The real explanation is a coincidence of timing: teeth start coming in right when babies lose their built-in immune protection and start putting everything in their mouths. That combination means more infections happen during the same window as teething, and parents naturally connect the two.
Why the Timing Lines Up So Perfectly
Most babies cut their first tooth around 6 months of age. Two other things happen at exactly the same time. First, the protective antibodies a baby received from their mother during pregnancy disappear. These antibodies build up during the second trimester, peak around birth, and are typically gone by six months. Second, babies hit a developmental milestone where they chew on everything they can grab: toys, fingers, furniture, the floor. Each new object introduces new germs directly into their mouths.
So a baby who develops a runny nose, mild fever, or diarrhea while cutting a tooth is almost certainly fighting off a virus or bacteria they picked up from their environment, not reacting to the tooth itself. The tooth just happened to show up at the same time. Seattle Children’s Hospital puts it plainly: these two factors, loss of maternal antibodies and chewing on everything, explain why infections spike between 6 and 12 months.
What Teething Actually Does to the Body
That said, teething isn’t completely symptom-free. When a tooth pushes through the gum, it triggers real inflammation at the site. Research published through the American Academy of Pediatric Dentistry found elevated levels of inflammatory signaling molecules in the gum tissue around erupting teeth. These molecules were correlated with specific symptoms: fever and sleep disturbances tracked with certain inflammatory markers, while digestive upset and appetite changes tracked with others.
The key distinction is scale. Teething can cause a slight rise in body temperature, but not a true fever. The American Academy of Pediatrics draws the line at 100.4°F (38°C). Anything at or above that threshold points to an actual illness, not teething. The inflammation from a tooth breaking through the gum is localized and mild. It can make a baby fussy, drooly, and uncomfortable, but it shouldn’t make them genuinely sick.
Symptoms Parents Report Most Often
In large cohort studies tracking hundreds of infants through their first year, the most commonly reported teething symptoms were excessive drooling (reported in about 68% of babies), irritability (40 to 65%), fever (38 to 50%), feeding difficulty (around 34%), diarrhea (35 to 36%), and sleep disturbance (about 32%). Around 73% of babies experienced at least some symptoms during teething.
These numbers are based on parent reports, which is an important caveat. Parents observing a fussy, feverish baby with a swollen gum naturally attribute everything to the tooth. Many of those fevers and bouts of diarrhea were likely mild infections that happened to coincide with eruption. Each teething episode typically lasts 3 to 8 days, with discomfort peaking in the days just before and after the tooth breaks through.
Symptoms That Aren’t From Teething
A few symptoms get blamed on teething that have no established connection to it. Vomiting, significant diarrhea, cough, and nasal congestion are signs of infection, not tooth eruption. A rash that spreads beyond the face (drool rash around the mouth is common and harmless) also points to illness. And again, any temperature at or above 100.4°F is a fever that warrants attention, not a teething side effect.
Ear pulling is one that confuses a lot of parents. Babies often tug at their ears while teething because the nerves in the jaw and ear share pathways, creating referred pain. But ear pulling can also signal an actual ear infection. If your baby has a fever along with the ear pulling, or seems to be in real distress, the ears are worth checking.
Loose Stools and Drooling
The connection between teething and diarrhea is one of the most persistent beliefs, but teething alone doesn’t cause it. What may happen is that sore gums encourage a baby to nurse or drink more frequently, increasing fluid intake and producing softer stools. That’s different from true diarrhea, which involves frequent, watery bowel movements and is almost always caused by a virus or bacteria. If your baby has multiple watery stools, especially with vomiting or fever, an infection is the more likely cause.
Safe Ways to Help With Teething Pain
The FDA has issued direct warnings against using topical gels containing benzocaine or lidocaine for teething pain. Benzocaine can cause a rare but serious condition where red blood cells lose their ability to carry oxygen effectively. Lidocaine solutions can cause seizures, heart problems, and severe brain injury if too much is applied or accidentally swallowed. Homeopathic teething tablets have also been flagged as unsafe. These products offer little to no benefit for teething and carry real risks.
What does work is simpler. Gently massaging your baby’s gums with a clean finger provides direct pressure on the sore spot. A firm rubber teething ring (not liquid-filled, not frozen) gives babies something safe to chew on. Frozen teethers can actually be hard enough to bruise swollen gums, so a cool one from the refrigerator is a better option. For babies who are clearly uncomfortable, your pediatrician can advise on appropriate pain relief based on your baby’s age and weight.
How to Tell Teething From Illness
The practical rule is straightforward. Teething causes mild, localized symptoms: fussiness, drooling, gum swelling, slight warmth, maybe a night or two of poor sleep. These symptoms cluster around the days a tooth is actively pushing through and resolve quickly. If your baby has a temperature above 100.4°F, a cough, runny nose, vomiting, diarrhea, a widespread rash, or seems lethargic and unlike themselves, something else is going on. The fact that a tooth is coming in at the same time doesn’t mean the tooth is the cause.
Babies in their first year catch an average of several viral infections, and most of those infections land right in the peak teething window. Understanding that overlap is the single most useful thing a parent can know, because it means you won’t dismiss a real illness as “just teething.”