The vast majority of babies sprout their first tooth when they're between 4 and 7 months old.
An early developer may get his first white cap as early as 3 months, while a late bloomer may have to wait until he's a year old or more. (In very rare cases, a baby's first tooth is already visible at birth.) Whenever the first tooth makes its appearance, celebrate the milestone by taking pictures and noting the date in your child's baby book.
Teeth actually start developing while your baby is in the womb and tooth buds form in the gums. Teeth break through one at a time over a period of months, and often – but not always – in this order: The bottom two middle teeth first, then the top two middle ones, then the ones along the sides and back. They may not all come in straight, but don't worry. They usually straighten out over time.
The last teeth to appear (the second molars, found in the very back of the mouth on the top and bottom) usually come in around your baby's third birthday. By age 3, your child should have a full set of 20 baby teeth, and they shouldn't start to fall out until his permanent teeth are ready to start coming in – around age 6.
Some experts disagree about whether teething actually causes symptoms, like fussiness, diarrhea, and fever, or whether these common symptoms are completely unrelated to teething and just coincidentally appear at the same time as emerging teeth. One of many possible explanations for these symptoms is that teething babies frequently put things in their mouths to soothe their gums, so they're coming into contact with more viruses and other germs.
Some babies get through teething with no problems at all, but many parents report that their babies do experience discomfort. The symptoms most likely to trouble a teether include:
Though many parents say their babies also have loose stools, a runny nose, or a fever just before a new tooth arrives, most experts don't think teething is to blame for these symptoms. The American Academy of Pediatrics says fever and diarrhea aren't normal symptoms of teething.
William Sears, pediatrician and author of The Baby Book, disagrees. Sears believes that teething can cause diarrhea and a mild diaper rash because your baby's excessive saliva ends up in his gut and loosens his stools. He also maintains that inflammation in the gums can cause a low fever (rectal temperature of less than 100.4 degrees Fahrenheit).
If your child has a rectal temperature of 101 degrees F or higher (100.4 degrees F or higher for babies younger than 3 months) and also has other symptoms, such as lethargy, lack of appetite, vomiting, or diarrhea, call his doctor to rule out anything more serious.