A baby’s inward thumb is the result of poor stretching of the muscles that stretch the thumb outward. Normally, your baby’s hands will gradually relax at two months and start to loosen gradually at three months. If your baby’s thumbs are still snapping inward beyond three months, there are two things to consider. On the one hand, brain injury, such as the existence of long-term chronic hypoxia in the newborn in utero, may cause cerebral ischemic-hypoxic encephalopathy at birth, intracranial hemorrhage, and neonatal pathological jaundice and other central brain injury, can lead to infant dystonia and manifest as internal thumb buckling. Secondly, post-traumatic nerve injury, some infants can be born with peripheral nerve damage to the hand can also lead to internal thumb buckling. Therefore, once a baby has an internal thumb buckle, parents should promptly take the child to the hospital for examination and symptomatic treatment after a clear diagnosis. The treatment of the baby’s inward thumb is based on physical therapy and local massage, and the purpose of the treatment is mainly to give the child functional and intellectual recovery.