Even at birth, your baby had a secret. All you saw was a gaping, gummy smile, but your child actually began developing tooth buds during the sixth week of fetal development, and all the groundwork for "baby teeth" were in place by the seventh month of pregnancy. So that tiny, seemingly toothless bundle of joy you held in the delivery room already had some teeth that were formed and others still in development -- all below the gum line.
Of course, just because those pearly whites have been around awhile doesn't mean it's easy to predict when teething -- the process of teeth growing through the gums to the surface -- will take place. Babies may begin teething as early as 3 months old, or well after their first birthday, but 6 months of age is a fairly common time for teething to begin.
Your child's behavior may clue you in to when it's almost time for a tooth to emerge, or "erupt," through the gums. Babies are often fussy for up to five days or so before a tooth breaks through. Their gums become tender, sore and swollen. Your little one also may veer away from normal eating habits because of the discomfort.