Babies usually start teething at 6 to 8 months, but the timing of teething varies from baby to baby, mainly related to genetics or the baby’s physical condition. A human being has two sets of teeth in his/her life, namely, milk teeth and permanent teeth, with a total of 20 milk teeth and 32 permanent teeth. At birth, there are already ossified milk teeth in the jawbone, which are covered by the gums. Generally 6~8 months after birth, the milk teeth begin to erupt, before the age of 3 years, the number of milk teeth within 2 years of age is about the age of the month minus 4~6. However, the eruption time, order of eruption and time of eruption of milk teeth have great individual differences. The order of eruption of milk teeth is generally lower jaw first than upper jaw, from front to back in the process of teething. Some babies in the process of tooth eruption may have increased saliva, drooling, irritability, sleep disturbance and other symptoms, these are normal physiological phenomena, after the teeth will be significantly relieved. If the baby’s teeth eruption is delayed, or the discomfort during the process of eruption is more serious, parents should take the baby to the hospital in time for a clear diagnosis and early treatment.