Most developmental milestones in a baby's life are cause for celebration: when they start crawling, the moment they take their first step, or when they finally say their first word. But one milestone that can be as frustrating as it is encouraging is when a baby starts teething. It's exciting because it means baby can start eating more solid foods and begin forming words since teeth are instrumental for speech. But the teething process can also be uncomfortable for baby − not to mention sometimes painful for nursing moms. 

Understanding when babies start teething can be helpful in planning ahead and providing the comfort and care your baby needs. 

When do babies start teething?

Various factors impact when a baby starts teething. These include whether a baby is having breastmilk alone or is taking formula and baby foods as well; plus whether the child is a boy or girl as girls tend to teethe about a month earlier than boys. Gestation may also play a part as one study found that babies who were in the womb longer and were larger at birth, cut their first tooth earlier than other babies. More than anything else though, "the timing of teething is influenced by genetics and can vary considerably," says Jason Nagata, MD, a pediatrician at UCSF Benioff Children’s Hospital in San Francisco. 

Due to such factors, there is no hard and fast rule about when a baby will begin teething, but there are some helpful guidelines. "A first tooth usually appears around 6 months old (some as early as 4 months), and most babies will develop teeth by 12 months," says Michelle Macias, MD, a professor of pediatrics and the director of the developmental-behavioral pediatrics fellowship program at the Medical University of South Carolina. She adds that the majority of children will usually have all their baby teeth by age 3.

What are signs my baby is teething? 

It's usually hard to miss when a baby starts teething as they often show signs of irritability even before their teeth cut through their gums. Once they do start to appear, Macias says a baby's two bottom front teeth - lower central incisors - are usually the first to appear, followed by the two top front teeth - upper central incisors.

Signs of discomfort to look out for include swollen or tender gums in the area where the tooth is coming in, and "your baby's temperature may slightly rise when teething," notes Macias. She adds, however, that fever-level temperatures "are not associated with teething." 

Other signs of teething include more drooling than usual, and your baby wanting to chew on more objects because they'll find the sensation soothing. Plan for sleep interruptions well. "Teething can lead to discomfort and pain, which in turn disrupts sleep," says Nagata. 

Is teething painful for babies? 

Indeed, these signs of discomfort during teething are so common because the process of cutting a tooth "can hurt," says Macias - though she says it "doesn't usually cause children too much discomfort." 

Nagata explains that any pain babies experience is usually caused by uneven edges of the tooth as it pushes against the gums, or the "pressure caused by the emerging teeth." Such discomfort can be soothed by various practices. The U.S. Food and Drug Administration (FDA) advises against using teething creams and gels and instead recommends gently rubbing or massaging swollen and tender gums with one's finger, or giving baby a chilled teething ring made of firm rubber to chew on. "Make sure the teething ring is not frozen," the agency notes. "If the object is too hard, it can hurt your child’s gums."